Colloquia are Wednesdays at 4:00 p.m. in DUAN G1B20, unless otherwise noted.

Coffee, tea and cookies will be available before regular colloquia beginning at 3:45 p.m. in DUAN G1B31.

### August 28 — "New frontiers for localization"

• Presenter:  Rahul Nandkishore, University of Colorado, Boulder
• Host:
• Abstract: Localization is a central paradigm for non-equilibrium quantum physics. I will explain what localization is, and why it is interesting, highlighting in particular some of the new phases that can arise in the localized regime, which have no equilibrium counterparts. I will then present some of my recent work demonstrating that localization can arise in settings where it was previously believed to be impossible, such as systems with long range interactions. I will conclude with a discussion of some recent developments, their implications, and an outlook for the field.

### September 4 — "Breaking Bias"

• Presenter: Stefanie Johnson, Leeds School of Business, University of Colorado, Boulder
• Host: Eric Cornell
• Abstract: In this talk, Johnson explains the biases that impede diversity initiatives and provides ways of overcoming those biases to effectively promote diversity in organizations. She specifically will talk about one example of a diversity intervention at the Hubble Space Telescope.  Johnson then covers strategies to interrupt unconscious biases though different cognitive mechanisms.

### September 11 — "In search of new scales of compositeness"

• Presenter: Ethan Neil, University of Colorado, Boulder
• Host:
• Abstract:  The study of particle physics has a long history of uncovering compositeness - new substructures within particles that were at first believed to be fundamental.  Are the current set of "fundamental" particles contained in the Standard Model hiding even smaller structures?  In this talk, I will explore the physics of composite particles, the current state of experimental searches for compositeness, and distinctive signatures of undiscovered strongly-coupled composite particles such as composite dark matter.

### September 18 — "New Detectors for Probing Our Universe"

• Presenter: Peter Graham, Stanford University
• Host: James K. Thompson
• Abstract: High precision technology offers a powerful new approach for particle physics and cosmology. In recent years there has been a surge of interest in using technologies such as atom interferometry, nuclear magnetic resonance, and high precision magnetometry in addition to the more traditional particle detection techniques. Excitingly, such technologies can allow the discovery of new physics which is otherwise completely undetectable by conventional techniques. For example the axion is one of the most strongly-motivated dark matter candidates, however to date only a small fraction of its parameter space has been explored. I will discuss several new experimental approaches to searching for this type of “ultralight” dark matter. Interestingly, these approaches are similar in many respects to gravitational wave detection. I will also discuss the use of atom interferometry for gravitational wave and dark matter detection and the new MAGIS detector. Such precision experiments will open new avenues for probing the origin and composition of the universe.

### September 25 — "Disorder as a driver of biological filtration"

• Presenter: Loren Hough, University of Colorado, Boulder
• Abstract: Intrinsically disordered proteins are flexible polymers that play a wide variety of vital cellular roles. Their disruption leads to a wide range of diseases, from cancer to neurodegeneration. Disordered proteins present a fascinating enigma; how they can be so important for cell function while remaining flexible and highly dynamic rather than forming well-defined structures? One role of intrinsically disordered proteins is to form the primary filter of the nuclear pore complex.  This remarkable filter allows the selective passage of some macromolecules while inhibiting the passage of others. We combine nuclear magnetic resonance spectroscopy within living cells, bench-top experiments and analytical models to show that binding to flexible filaments can give rise to unexpected diffusive properties that contribute to motion through biological filters.

### October 2 — "Network architectures supporting learnability"

• Presenter: Danielle Bassett, University of Pennsylvania
• Host: Loren Hough
• Abstract: Human learners acquire not only disconnected bits of information, but complex interconnected networks of relational knowledge. The capacity for such learning naturally depends on the architecture of the knowledge network itself. I will describe recent work assessing network constraints on the learnability of relational knowledge, and theories from statistical physics that offer an explanatory model for such constraints. I will then broaden the discussion to the generic manner in which humans communicate using systems of interconnected stimuli or concepts, from language and music, to literature and science. I will describe an analytical framework to study the information generated by a system as perceived by a biased human observer, and provide experimental evidence that this perceived information depends critically on a system's network topology. Applying the framework to several real networks, we find that they communicate a large amount of information (having high entropy) and do so efficiently (maintaining low divergence from human expectations). Moreover, we also find that such efficient communication arises in networks that are simultaneously heterogeneous, with high-degree hubs, and clustered, with tightly-connected modules -- the two defining features of hierarchical organization. Together, these results suggest that many real networks are constrained by the pressures of information transmission to biased human observers, and that these pressures select for specific structural features.

### October 9 — "Discovering Neutrino Properties with Long-Baseline Beams"

• Presenter: Alysia Marino, University of Colorado, Boulder
• Host: John Cumalat
• Abstract: Neutrinos are fundamental particles with no electric charge and as-yet-unmeasured masses, allowing them to travel unimpeded through enormous amounts of material.  Despite their elusiveness, a lot of compelling evidence shows that neutrinos have non-zero masses and change from one flavor to another. Intense neutrino beams generated by particle accelerators are now being used in order to more precisely probe the physics of neutrino masses and mixing.
This talk will briefly review the experimental evidence and the framework that describes neutrino oscillations. As an example of a man-made neutrino beam, it will focus on the Tokai-to-Kamioka (T2K) experiment, which creates a beam of muon neutrinos at J-PARC on the east coast of Japan.  With two neutrino detectors, one located near the origin of the beam, and another located 295 km away, T2K has seen the disappearance of muon neutrinos and the appearance of electron neutrinos. The talk will conclude with a brief discussion of future long-baseline neutrino experiments, especially the efforts in the US to send a high-intensity beam of neutrinos from Fermilab to a former gold mine in South Dakota.

### October 16 — "Controlling magnetism in a Mott insulator by optical pumping"

• Presenter: David Hsieh, California Institute of Technology
• Host: Rahul Nandkishore
• Abstract: Controlling magnetism in an antiferromagnetic Mott insulator with ultrashort optical pulses can lead to both advances in our fundamental understanding of out-of-equilibrium interacting quantum matter as well as to novel high-speed information storage and processing technologies. However, optically manipulating antiferromagnetic order and detecting its out-of-equilibrium behaviors have proven difficult owing to various factors such as the absence of net magnetization and the ultrafast timescales involved. In this talk, I will describe a novel time-resolved nonlinear optical polarimetry technique that is capable of measuring ultrafast changes in magnetic symmetry. I will then describe how we have deployed this technique to reveal an unusual out-of-equilibrium critical behavior of the magnetic order in an optically pumped Mott insulator that circumvents the laws of equilibrium thermodynamics.

### October 23 — "Frontiers of topological quantum matter and beyond"

• Presenter: Michael Hermele, University of Colorado, Boulder
• Host: John Cumalat
• Abstract: The last ten to fifteen years have witnessed extraordinary progress in the theory of topological quantum matter.  This includes the discovery of new families of quantum phases of matter, going hand-in-hand with unprecedented advances in the systematic understanding of what phases are possible in principle.  Progress has been particularly pronounced within a certain context that includes many physically interesting systems, but also leaves a vast frontier to explore.  In this talk, I will describe two recent lines of work, one of which lies at this frontier, while the second crosses into non-topological’’ territory.
First, I will discuss crystalline topological phases, those where the geometrical symmetries of crystalline solids play an important role.  Before the last few years, little was understood about such phases for strongly interacting systems, and obtaining such understanding was believed to be a hard problem.  Surprisingly, due to previously hidden structure that my work uncovered, obtaining a systematic classification of crystalline topological phases turns out to be easier than for their non-crystalline counterparts.
Second, I will discuss so-called fracton phases of matter.  While fracton phases share some features in common with topological phases, they are not topological.  I will describe my work drawing connections between fracton phases and more familiar topological phases, and my ongoing contributions to the development of a theoretical framework for fracton matter.

### October 30 — "Bringing Down the Cost of Fusion Power"

• Presenter: Steven Cowley, Princeton Plasma Physics Laboratory
• Host: Dmitri Uzdensky
• Abstract: The scientific demonstration of a self-sustained fusion burn in the international experiment ITER — is within sight. However, commercial fusion power will require further innovation to bring down the cost and complexity of fusion systems. I will describe recent advances in the science, design and technology of three-dimensional confinement devices (stellarators) that promise simpler and cheaper fusion reactors.

### November 6 — "Making microwaves with light at the quantum limit and beyond"

• Presenter: Thomas Schibli, University of Colorado, Boulder
• Host: John Cumalat
• Abstract: Precision measurements enabled by exquisitely stable optical sources had a profound impact on Boulder’s current scientific enterprise. This talk will start with an overview of fundamental noise processes in oscillators, and highlight some of the major differences between electronic and optical sources. I will then discuss what levels of stability can be reached directly from a laser to date, and how to occasionally dip far below the quantum limit for specific applications.
As a practical application, I will elaborate on the generation of laser-driven, ultra-low noise microwaves, now readily surpassing the best room-temperature microwave sources at a fraction of their size, weight and power.

### November 13 — "Quantum metrology at the 19th decimal place"

• Presenter: David Leibrandt, NIST, University of Colorado Boulder
• Host: John Cumalat
• Abstract: The tools of trapped-ion quantum logic can be used to enable and enhance precision measurements, with applications in time and frequency metrology and the search for physics beyond the standard model.  In this talk, I will describe optical atomic clocks based on Al+ which operate at this fertile intersection of fields.  These clocks use quantum-logic gates with a co-trapped second ion species for preparation and readout of the Al+ state, and offer the tantalizing prospect of Heisenberg-limited measurements with entangled ions.  Recent progress, including an improved ion trap design and sympathetic laser cooling to the 3D ground state, has enabled total fractional systematic uncertainty below 10-18.  We have performed frequency ratio measurements between Al+, Sr, and Yb clocks with uncertainty below 10-17, which can be used to place constraints on possible temporal variations of fundamental constants and models of ultralight dark matter.

### November 20 — "Does an isolated quantum system relax?"

• Presenter: Joerg Schmiedmayer, Vienna Center for Quantum Science and Technology (VCQ) Atominstitut – Institute of Atomic and Subatomic Physics Technische Universität
• Host: Ana Maria Rey
• Abstract: The evolution of an isolated quantum system is unitary.  This is simple to probe for small systems consisting of few particles.  But what happens if the system becomes large and its constituents interact?
In a first set of experiments, we study a weak quench introducing quantum noise. The coherence created by coherent splitting of a 1d quantum gas degrades by coupling to the many internal degrees of freedom available [1].  The system relaxes to a pre-thermalisatized quasi steady state [2] described by a generalized Gibbs ensemble [3] which emerges through a light cone like spreading of ’de-coherence’ [4]. By engineering the Quasiparticles we can get coherence back by many body quantum revivals [5].  We conjecture that our experiments point to a universal way through which relaxation in isolated many body quantum systems proceeds if the low energy dynamics is dominated by scrambling of the eigenmodes of long lived excitations [6].
In a second set of experiments we study a strong cooling quench and demonstrate universal scaling in time and space, associated with the approach of a non-thermal fixed point [7]. The time evolution within the scaling period is described by a single universal function and scaling exponent, independent of the species of the initial state which constitutes a crucial step in the verification of universality far from equilibrium. If successful, this will lead to a comprehensive classification of systems far from equilibrium based on their universal properties similar to the universality classes in phase transitions.  and be the basis for a new type of quantum simulation that let us explore a large variety of systems at different scales.
Work performed in collaboration with the groups of E. Demler (Harvard), Th. Gasenzer und J. Berges (Heidelberg). Supported by the Wittgenstein Prize, the FWF SFB FoQuS, DFG-FWF: SFB ISOQUANT: and the EU: ERC-AdG QuantumRelax
[1] S. Hofferberth et al. Nature, 449, 324 (2007).
[2] M. Gring et al., Science, 337, 1318 (2012); D. Adu Smith et al. NJP, 15, 075011 (2013).
[3] T. Langen et al., Science 348 207-211 (2015).
[4] T. Langen et al., Nature Physics, 9, 640–643 (2013).
[5] B. Rauer et al. Science 360, 307310 (2018).
[6] T. Langen, T. Gasenzer, J. Schmiedmayer, J. Stat. Mech.  064009 (2016)
[7] S. Erne et al. Nature 253, 225 (2018).

### December 4 — "Evaluating the Iran Nuclear Deal"

• Presenter: Ron Soltz, Lawrence Livermore National Laboratory
• Host: Jamie Nagle
• Abstract: The Iran Nuclear Deal evokes strong reactions.  It has been called "The Worst Deal Ever" as well as "The best option for preventing Iran from obtaining a nuclear weapon.  Otherwise known as the "Joint Comprehensive Plan of Action", the JCPOA has led to much debate, even if little of it has been substantive.  Put into effect in 2015, the JCPOA continues to influence the behavior of the EU, China, and Russia, while the U.S. formally withdrew in May 2018 and Iran has recently begun to violate the agreement in stages.
The JCOPOA is unique in the history of international agreements, but as it stands at the intersection of science and policy, it is also a valuable teaching tool for the role that science can play in formulating good policy, while also providing an opportunity to review a few basic concepts in nuclear physics.  I will review the basic components of the JCPOA and explain their origin.  The agreement will also be placed in the context of past nuclear arms agreements and U.S. nuclear non-proliferation policy.  I will review criticisms and flaws of the agreement. Future implications for Iran and global non-proliferation efforts will also be discussed.

### December 11 — "The Challenge of a nuclear optical clock: recent progress and perspectives"

• Presenter: Lars von der Wense, Ludwig-Maximilians-University of Munich
• Host: Jun Ye
• Abstract: A nuclear optical clock based on a single 229Th ion is expected to achieve a higher accuracy than the best atomic clocks operational today [1]. Although already proposed back in 2003 [2], such a nuclear frequency standard has not yet become reality. The main obstacle that has so far hindered the development of a nuclear clock is an imprecise knowledge of the energy value of a nuclear excited state of the 229Th nucleus, generally known as the 229Th isomer. This metastable nuclear excited state is the one of lowest energy in the whole nuclear landscape and - with an energy of less than 10 eV - offers the potential for nuclear laser spectroscopy, which poses a central requirement for the development of a nuclear clock. In the past few years significant progress toward the development of a nuclear frequency standard has been made: Starting with a first direct detection of the 229Th isomer in 2016 based on its internal conversion decay channel [3], the isomeric lifetime could be determined in 2017 [4], followed by a first laser-spectroscopic characterization in 2018 [5]. Most recently, a first energy determination based on the isomer’s direct detection was successful [6]. This new knowledge provides, in combination with an achieved drastically enhancement of XUV-frequency comb intensity [7], the basis for improved efforts toward the laser-based search for the nuclear transition [8, 9], which can ultimately lead to the development of a nuclear optical clock. In this presentation I will give an overview over the current status of the nuclear clock development, with a particular focus on the most recent progress. Also the next required steps will be detailed and future perspectives will be given.
• References
[1] C.J. Campbell et al., Phys. Rev. Lett. 108, 120802 (2012).
[2] E. Peik and C. Tamm, Eur. Phys. Lett. 61, 181 (2003).
[3] L. von der Wense et al., Nature 533, 47 (2016).
[4] B. Seiferle et al., Phys. Rev. Lett. 118, 042501 (2017).
[5] J. Thielking et al., Nature 556, 321 (2018).
[6] B. Seiferle et al., Nature 573, 243 (2019).
[7] G. Porat et al., Nature Photonics 12, 387 (2018).
[8] L. von der Wense, Phys. Rev. Lett. 119, 132503 (2017).
[9] L. von der Wense and C. Zhang, arXiv:1905.08060 (2019).

For more information about colloquia this semester, contact: Rahul Nandkishore.

Colloquia are Wednesdays at 4:00 p.m. in DUAN G1B20, unless otherwise noted.

Coffee, tea and cookies will be available before regular colloquia beginning at 3:45 p.m. in DUAN G1B31.

### January 16 — "Unleashing Liquid Argon Time Projection Chambers for Neutrino Physics: MicroBooNE, SBN, and DUNE"

• Presenter: Michael Mooney, Colorado State University
• Host: Eric Zimmerman
• Abstract: The neutrino is the most abundant massive particle in our universe, originating from the Sun, the Earth’s core and atmosphere, supernovae, the Big Bang, and man-made sources such as nuclear reactors and particle accelerators. Despite its omnipresence, it remains the least understood known fundamental particle due to its weak interactions with other particles (and thus particle detectors). One promising detector technology that can be used to study the neutrino in great detail is the liquid argon time projection chamber (LArTPC), an imaging detector that can be used to "photograph" neutrino-nucleus interaction events. Three LArTPC neutrino experiments in the US, MicroBooNE (Micro Booster Neutrino Experiment), the SBN (Short-Baseline Neutrino) Program, and DUNE (Deep Underground Neutrino Experiment) are discussed, including the status of each experiment and recent results.

### January 23 — "Observations and Discoveries of Our Heliosphere’s Interstellar Interaction"

• Presenter: Dave McComas, Princeton University
• Host: Mihaly Horanyi
• Abstract: The solar wind and its embedded magnetic field flow outward from the sun in all directions, inflating a bubble in the local interstellar medium called the heliosphere. Prior to 2004, there were very few direct observations of the interaction of the heliosphere and local interstellar medium and our knowledge of these regions was largely theoretical. Then, 2004 and 2007 the Voyager 1 and 2 spacecraft crossed the heliosphere’s termination shock and in 2012 and 2018, each went on to cross the heliopause and entered interstellar space. IBEX – the Interstellar Boundary Explorer – launched in 2008, and has been returning 3-D global observations of ion distributions in the heliosheath and beyond via charge exchange Energetic Neutral Atoms (ENAs), continuously since then. These sets of observations are highly complementary with the Voyagers providing detailed in situ measurements along their two trajectories and IBEX returning all-sky maps of ENAs with energies from <0.1 to ~6 keV. Over the past decade and a half, these observations have led to numerous discoveries and “firsts” and a true scientific revolution in our understanding of the outer heliosphere and its interstellar interaction. With the continuation of the Voyagers and IBEX, and NASA’s recent selection of the Interstellar Mapping and Acceleration Probe (IMAP) to launch in 2024, the heliophysics community can look forward to many more years of outstanding new observations and innovative science. This seminar is adapted from the Parker Lecture recently presented at the 2018 Fall AGU meeting, includes connections to planned contributions to IMAP from CU/LASP, summarizes some of the biggest discoveries and most intriguing mysteries of the fascinating region that surrounds our Sun and forms our home in the galaxy.

### **Special Colloquium: Thursday, January 24** — "Synthetic Quantum Matter in Superconducting Circuits"

• Presenter: Alex Ruichao Ma, University of Chicago
• NOTE SPECIAL LOCATION: JILA Auditorium
• Host: Konrad Lehnert
• Abstract: Superconducting circuits have emerged as a competitive platform for quantum computation, satisfying the challenges of controllability, long coherence and strong interactions. Here we apply this toolbox to the exploration of strongly correlated quantum materials made of microwave photons. We develop a versatile recipe that uses engineered dissipation to stabilize many-body phases, protecting them against intrinsic photon losses. We build a strongly interacting Bose-Hubbard lattice in circuits and applied our dissipative stabilization method to create a Mott insulator of photons. Site- and time-resolved microscopy provides insights into the thermalization processes through the dynamics of defects in the Mott phase. In another experiment, we realize a superconducting Chern insulator constructed from tunnel-coupled, time-reversal broken microwave cavities and study its topologically protected edge states. Our work demonstrates the power of superconducting circuits for studying synthetic quantum matter in both coherent and driven-dissipative settings. I will briefly discuss future prospects including microscopic studies of strongly interacting topological phases and quantum thermodynamics.

### **Special Colloquium: Monday, January 28** — "Quantized States, Berry Phases, and Quantum-Hall Wedding-Cake structures in Graphene Quantum Dots"

• Presenter: Fereshte Ghahari, NIST
• NOTE SPECIAL LOCATION: DUAN G130
• Host: Konrad Lehnert
• Abstract: Recent progress in creating graphene quantum dots (QDs) with fixed build-in potentials has offered a new platform to visualize and probe the confined electronic states. In this talk, I describe scanning tunneling spectroscopy measurements of the energy spectrum of graphene QDs as a function of energy, spatial position, and magnetic field. In zero field, the charge carriers are confined by oblique Klein scattering at the p-n junction boundary giving rise to a series of quasi-bound single particle states. Applying a weak magnetic field, we observe a giant and discontinuous change in the energy of time-reversed angular-momentum states, which manifests itself as the appearance of “new” resonances in the tunneling density of states. This behavior corresponds to the on/off switching of a π- Berry phase when a weak critical magnetic field is reached.  With increased applied magnetic field, the QD states can be confined even further as they condense into highly degenerate Landau levels providing the first spatial visualization of the interplay between spatial and magnetic confinement. This is observed as formation of the seminal wedding-cake structures of concentric compressible and incompressible density rings in strong magnetic fields.

### January 30 — "Laboratory Plasma Astrophysics: from Angular Momentum Transport to Magnetic Reconnection"

• Presenter: Hantao Ji, Princeton University
• Host: Dmitri Uzdensky
• Abstract: Studying astrophysical plasma processes in the lab becomes increasingly possible and exciting, complementing numerical simulations. In this talk, I will describe two examples of experimental efforts with which I am closely involved. The first one is about the mechanisms of rapid angular momentum transport required to explain the observed fast accretion, e.g,, enabling star formation and powering quasars. By carefully isolating effects due to artificial boundaries, key astrophysical questions regarding hydrodynamic and magnetohydrodynamic (MHD) instabilities can be uniquely studied in the laboratory. The second example is about the mechanisms of fast magnetic reconnection, considered to be at the core of the observed flares from various astrophysical objects including our Sun. Plasma physics beyond MHD has been identified as a key to fast reconnection in effectively small plasmas, while understanding how fast reconnection works in effectively large astrophysical plasmas is at the current frontier of research. Future prospects of this growing field of laboratory plasma astrophysics will be discussed.

### **Special Colloquium: Thursday, January 31** — "Ultracold Molecules: From Quantum Chemistry to Quantum Computing"

• Presenter: Alan Jamison, Massachusetts Institute of Technology
• NOTE SPECIAL LOCATION: JILA Auditorium
• Host: Konrad Lehnert
• Abstract: Cooling atomic gases to quantum degeneracy opened the new field of quantum simulation. Here the precise tools of atomic physics can be used to study exotic models from condensed matter or nuclear physics with unique tunability and control. Ultracold molecules bring many new possibilities to quantum simulation. I will review the physics of ultracold molecules, including our recent production of stable, ultracold triplet molecules and what they can add to quantum simulation. I will also discuss our recent work using ultracold molecules to study chemical reactions with complete quantum state control. All of these tools and ideas come together in a proposal to use ultracold molecules as a new platform for quantum computing.

### **Special Colloquium: Monday, February 4** — "Quantum nanophotonics: engineering atom-photon interactions on a chip"

• Presenter: Shuo Sun, Stanford University
• NOTE SPECIAL LOCATION: DUAN G130
• Host: Konrad Lehnert
• Abstract: The ability to engineer controllable atom-photon interactions is at the heart of quantum optics and quantum information processing. In this talk, I will introduce a nanophotonic platform for engineering strong atom-photon interactions on a semiconductor chip. I will first discuss an experimental demonstration of a spin-photon quantum transistor [1], a fundamental building block for quantum repeaters and quantum networks. The device allows a single spin trapped inside a semiconductor quantum dot to switch a single photon, and vice versa, a single photon to flip the spin. I will discuss how the spin-photon quantum transistor realizes optical nonlinearity at the fundamental single quantum level, where a single photon could switch the transmission of multiple subsequent photons [2]. I will next discuss the promise of realizing photon-mediated many-body interactions in an alternative solid-state platform based on a more homogeneous quantum emitter, silicon-vacancy (SiV) color centers in diamond. I will introduce our efforts in creating strong light-matter interactions through photonic crystal cavities fabricated in diamond [3], and the use of cavity-stimulated Raman emission to overcome the remaining frequency inhomogeneity of the emitters [4]. Finally, I will outline the exciting prospects of applying inverse designed nanophotonic structures into quantum optics, and their potential applications in engineering photon-mediated atom-atom interactions.

References
[1] S. Sun et al., Nature Nanotech. 11, 539–544 (2016).
[2] S. Sun et al., Science 361, 57-60 (2018).
[3] J. L. Zhang* and S. Sun* et al., Nano Lett. 18, 1360–1365 (2018).
[4] S. Sun et al., Phys. Rev. Lett. 121, 083601 (2018)

### February 6 — "Correlations in moire flat bands: topological order, symmetry breaking, and superconductivity"

• Presenter: Andrea Young, UC Santa Barbara
• Host: Adam Kaufman
• Abstract: Van der Waals heterostructures are constructed by layering atomically thin crystals such as graphene, with interlayer bonding provided by the van der Waals force. When neighboring crystal lattices are slightly mismatched, a moire pattern forms from the beating of two slightly mismatched lattices.  Moire patterns can be used to generate artificial lattices for electrons, providing a versatile platform for engineering electronic structure.  Of particular interest is the possibility of engineering flat electronic bands where correlations dominate in determining the electronic ground state.  I will describe how these artificial lattices can be used to realize several exotic states of matter, including states where electrons appear to 'break up'--localizing a fractional of a charge on each lattice site--as well as states where electrons pair up to form a superconductor, all realized in atomically thin sheets of carbon.

### **Special Colloquium: Monday, February 11** — "Measurement of the fine-structure constant as a test of the Standard Model"

• Presenter: Richard Parker, University of California, Berkeley
• NOTE SPECIAL LOCATION: DUAN G130
• Host: Konrad Lehnert
• Abstract: Measurements of the fine-structure constant alpha require methods from several subfields and are thus powerful tests of the consistency of theory and experiment in physics. Using the recoil frequency of cesium-133 atoms in a matter-wave interferometer, we recorded the most accurate measurement of the fine-structure constant to date: alpha = 1/137.035999046(27) at 2.0 x 10^-10 accuracy. Using multiphoton interactions (Bragg diffraction and Bloch oscillations), we demonstrate the largest phase (12 million radians) of any Ramsey-Borde interferometer and control systematic effects at a level of 0.12 parts per billion. Comparison with Penning trap measurements of the electron gyromagnetic anomaly ge-2 via the Standard Model of particle physics is now limited by the uncertainty in ge-2; a 2.5 sigma tension rejects dark photons as the reason for the unexplained part of the muon's magnetic moment at a 99 percent confidence level. Implications for dark-sector candidates and electron substructure may be a sign of physics beyond the Standard Model that warrants further investigation.

### February 13 — "X-ray sources from laser-plasma acceleration: development and applications for high energy density sciences"

• Presenter: Félicie Albert, Lawrence Livermore National Laboratory
• Host: John Cary and Michael Litos
• Abstract: Bright sources of x-rays, such as synchrotrons and x-ray free electron lasers (XFEL) are transformational tools for many fields of science. They are used for biology, material science, medicine, or industry. Such sources rely on conventional particle accelerators, where electrons are accelerated to gigaelectronvolts (GeV) energies. The accelerating particles are also wiggled in magnetic structures to emit x-ray radiation that is commonly used for molecular crystallography, fluorescence studies, chemical analysis, medical imaging, and many other applications.  One of the drawbacks of synchrotrons and XFELs is their size and cost, because electric field gradients are limited to about a few 10s of MeV/M in conventional accelerators.
This seminar will review particle acceleration in laser-driven plasmas as an alternative to generate x-rays. A plasma is an ionized medium that can sustain electrical fields many orders of magnitude higher than that in conventional radiofrequency accelerator structures. When short, intense laser pulses are focused into a gas, it produces electron plasma waves in which electrons can be trapped and accelerated to GeV energies. This process, laser-wakefield acceleration (LWFA), is analogous to a surfer being propelled by an ocean wave. Betatron x-ray radiation, driven by electrons from laser-wakefield acceleration, has unique properties that are analogous to synchrotron radiation, with a 1000-fold shorter pulse. This source is produced when relativistic electrons oscillate during the LWFA process.
An important use of x-rays from laser plasma accelerators we will discuss is in High Energy Density (HED) science. This field uses large laser and x-ray free electron laser facilities to create in the laboratory extreme conditions of temperatures and pressures that are usually found in the interiors of stars and planets. To diagnose such extreme states of matter, the development of efficient, versatile and fast (sub-picosecond scale) x-ray probes has become essential. In these experiments, x-ray photons can pass through dense material, and absorption of the x-rays can be directly measured, via spectroscopy or imaging, to inform scientists about the temperature and density of the targets being studied.
Work performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under contract DE-AC52-07NA27344, supported by the LLNL LDRD program under tracking code 13-LW-076, 16-ERD-024, 16-ERD-041, supported by the DOE Office of Fusion Energy Sciences under SCW 1476 and SCW 1569, and by the DOE Office of Science Early Career Research Program under SCW 1575

### February 20 — "Effective Field Theories & Modifying Gravity: The View from Below"

• Presenter: Cliff Burgess, Perimeter Institute and MacMaster University
• Host: Shanta DeAlwis
• Abstract: We live at a time of contradictory messages about how successfully we understand gravity. General Relativity seems to work very well in the Earth’s immediate neighbourhood, but arguments abound that it needs modification at very small and/or very large distances. This talk tries to put this discussion into the broader context of similar situations in other areas of physics, and summarizes some of the lessons which our good understanding of gravity in the solar system has for proponents for its modification over very long and very short distances. The main message is that effective theories (in the technical sense of effective) provide the natural (and arguably only known) precise language for framing proposals. Its framework is also useful, inasmuch as it makes some modifications seem more plausible than others, though there are also some surprises. Amongst the surprises is evidence that in some ways gravity behaves more like condensed matter physics or optics than particle physics, raising the possibility that tools from these areas may play a useful role in understanding puzzles with cosmology and black holes.

### **Special Colloquium: Thursday, February 21** — "Engineering Trapped-Ion Systems for Large Scale Quantum Simulation"

• Presenter: Guido Pagano, University of Maryland and NIST
• NOTE SPECIAL LOCATION: JILA Auditorium
• Host: Konrad Lehnert
• Abstract: Laser cooled trapped ions offer unprecedented control over both internal and external degrees of freedom at the single-particle level. They are considered among the foremost candidates for realizing quantum simulation and computation platforms that can outperform classical computers at specific tasks. In this talk I will show how linear arrays of trapped 171Yb+ ions can be used as a versatile platform for studying quantum dynamics of strongly correlated many-body quantum systems. In particular I will describe how to realize time-crystalline phases in a Floquet setting, where the spin system exhibits persistent time-correlations under many-bodylocalized dynamics [1]. I will also present our observation of a new type of out-of equilibrium dynamical phase transition in a spin system with over 50 spins [2]. Moreover I will show our latest efforts towards scaling up the trapped-ion quantum simulator [3] using a cryo-pumped vacuum chamber where we can trap more than 100 ions indefinitely. The reliable production and lifetime of large linear ion chains enabled us to investigate quasi-particle excitations showing confinement in the quench dynamics [4] and the implementation of Quantum Approximate Optimization Algorithms (QAOA) [5].
References:
[1] J. Zhang et al., Nature, 543, 217 (2017)
[2] J. Zhang, G. Pagano, et al., Nature, 551, 601 (2017)
[3] G. Pagano et al., Quantum Sci. Technol., 4, 014004 (2019)
[4] F. Liu, et al., arXiv 1810.02365 (2018)
[5] G.Pagano, et al., (in preparation 2019)

### February 27 — "Machine learning the quantum many-body problem"

• Presenter: Roger Melko, University of Waterloo
• Host: Leo Radzihovsky
• Abstract: The quantum wavefunction presents the ultimate "big data" problem in physics.  When many quantum particles interact in a low-temperature material or a quantum computer, the complexity of the quantum state presents a daunting challenge for any classical simulation strategy.  Recently, a new computational toolbox based on modern machine learning techniques has been rapidly adopted into the field of condensed matter and quantum information physics. Standard tools like feed-forward and convolutional neural networks are being repurposed for training on "images" of microscopic configurations.  Unsupervised and reinforcement learning are making headway in improving standard algorithms such as quantum Monte Carlo.  In this talk, I will discuss recent progress, focussing on how generative modelling with stochastic neural networks can be used to combat the complexity of the quantum wavefunction, with applications in materials science, atomic physics, and the design of future quantum computers.

### March 6 — "Quantum Logic Control of a Single Molecular Ion"

• Presenter: Dietrich Leibfried, Ion Storage Group, NIST
• Host: Ana Maria Rey
• Abstract: An amazing level of quantum control is routinely reached in modern experiments with atoms, but similar control over molecules has been an elusive goal. We recently proposed a method based on quantum logic spectroscopy [1] to address this problem for a wide class of molecular ions [2]. We have now realized the basic elements of this proposal.
In our demonstration, we trap a calcium ion together with a calcium hydride ion (CaH+) that is a convenient stand-in for more general molecular ions. We cool the two-ion crystal to its motional ground state and then drive motional "sidebands" of Raman transitions in the molecular ion, meaning that a transition in the molecule is accompanied by a single quantum of excitation in the motion of the ion pair. We can efficiently detect this single quantum with the calcium ion, which projects the molecule into the final state of the sideband transition, a known, pure quantum state.
The molecule can be coherently manipulated after the projection, and its resulting state read out by another quantum logic state detection [3]. We demonstrate this by driving Rabi oscillations between rotational states. All transitions we address in the molecule are either driven by a single, far off-resonant continuous-wave laser or by a far-off-resonant frequency comb. This makes our approach applicable to control and precision measurement of a large class of molecular ions.
[1] P.O. Schmidt, et al. Science 309, 749 (2005)
[2] D. Leibfried, New J. Phys. 14, 023029 (2012)
[3] C.-W. Chou, et al. Nature 545, 203 (2017)

### March 13 — "Engaging students in Modeling Instruction: developing and studying students as scientists"

• Presenter: Eric Brewe, Drexel University
• Host: Noah Finkelstein
• Abstract: Physics Education Research is both about improving instruction and understanding the fundamentals of what learning is and how learning manifests in its many forms. In this talk I describe the development of Modeling Instruction (MI) for University Physics as a research endeavor into improving instruction. Modeling is built on the idea that all science proceeds through an iterative process of model development, evaluation, deployment, and revision. Accordingly, effective science instruction should promote the development of modeling skills by engaging students in the practices of modeling. I describe research within the context of MI classes as the basis for understanding learning broadly. Over the course of this talk I will summarize the theoretical foundations for MI, and describe research that translates the theory into practice in the MI classroom. Drawing on the MI classroom as a context for research, I will report on findings including: improved conceptual understanding, positive attitudinal shifts, the growth of student networks, and even changes to the neurobiology that underpins physics reasoning. Finally, I will describe how these research findings drive further questions and understanding of learning generally.

### March 20 — "New results from the NOvA neutrino oscillation experiment"

• Presenter: Patricia Vahle, College of William & Mary
• Host: Alysia Marino
• Abstract: Neutrino oscillations provide the first hints at physics beyond the standard model of particle physics. Current and future neutrino experiments aim to further refine our understanding of neutrino mixing and reveal the remaining unknowns in the process. Precision measurements in long-baseline accelerator experiments could help answer profound questions about the origin and evolution of our universe, including the assymetry of matter over antimatter. The NOvA experiment at Fermilab uses a beam of neutrinos and two detectors separated by an 810 km baseline to observe muon neutrino disappearance and electron neutrino appearance. These measurements have the potential to resolve the ordering of the neutrino masses, called the hierarchy, determine whether the mixing angle theta_23 is maximal, and if not in which octant it lies, and perhaps even hint at the violation of CP in the neutrino sector. In this talk, I'll describe the current status of accelerator oscillation experiments seeking to answer these questions, and in particular present new results from the NOvA experiment.

### April 3 — "Topological Insulators to Weyl Fermions and Beyond"

• Presenter: M. Zahid Hasan, Princeton University
• Host: Margaret Murnane and Dan Dessau
• Abstract: Electrons in solids organize in ways to give rise to distinct phases of matter such as insulators, metals, magnets or superconductors. In the last ten years or so, it has become increasingly clear that in addition to the symmetry-based classification of matter, topological consideration of electronic wavefunctions plays a key role in determining distinct phases of matter [see, for an introduction, Hasan & Kane, Reviews of Modern Physics 82, 3045 (2010)].

In this talk, I introduce these concepts in the context of their experimental realizations in real materials leading to recent developments. As an example, I present how tuning a 3D topological insulator whose surface hosts an unpaired Dirac fermion can give rise to topological superconductors with helical Cooper pairing leading to novel Majorana platforms, Weyl fermion semimetals with “fractional” surface Fermi surfaces, and other topological nodal and magnetic states of matter. These topological materials harbor novel properties that may lead to the development of next generation quantum technologies accelerating the second quantum revolution.

### April 10 — "New opportunities in dark matter at accelerators"

• Presenter: Nhan Tran, Fermilab
• Host: Keith Ulmer
• Abstract: The program to search for dark matter in the past couple of decades has mostly focused on the WIMP (weakly interacting massive particle) at the GeV - TeV scale. It has made impressive strides in sensitivity but has yet to unearth the particle nature of dark matter. Recently there have been many new initiatives to broaden the search for dark matter, many of them smaller scale experiments. Recently, within the US, there has been an effort to organize and contrast various experimental techniques and their sensitivity. One of the main thrusts of this dark matter initiative is to extend searches for dark matter below a GeV using accelerator techniques. I will discuss the status of this dark matter initiative and focus on the opportunities for dark matter at accelerators. I will lay out the various accelerator approaches to look for sub-GeV dark matter including beam dump and fixed target missing momentum techniques. As a specific example, I will go into detail on the missing momentum technique effort in which I am involved.

### April 17 — "Quantum Magnetism from the Iron Age to Today"

• Presenter: Dan Arovas, UCSD
• Host: Leo Radzihovsky
• Abstract: The quantum theory of magnetism has provided many durable paradigms for quantum phases of matter, including intrinsically quantum disordered states, symmetry-protected topological phases, and quantum spin liquids.  In this lecture, I will review some of the history and highlights of this very rich field.

### April 24 — "Magic Angle Graphene: a New Platform for Strongly Correlated Physics"

• Presenter: Pablo Jarillo-Herrero, MIT
• Host: Dan Dessau
• Abstract: The understanding of strongly-correlated quantum matter has challenged physicists for decades. Such difficulties have stimulated new research paradigms, such as ultra-cold atom lattices for simulating quantum materials. In this talk I will present a new platform to investigate strongly correlated physics, based on graphene moiré superlattices. In particular, I will show that when two graphene sheets are twisted by an angle close to the theoretically predicted ‘magic angle’, the resulting flat band structure near the Dirac point gives rise to a strongly-correlated electronic system. These flat bands exhibit half-filling insulating phases at zero magnetic field, which we show to be a correlated insulator arising from electrons localized in the moiré superlattice. Moreover, upon doping, we find electrically tunable superconductivity in this system, with many characteristics similar to high-temperature cuprates superconductivity. These unique properties of magic-angle twisted bilayer graphene open up a new playground for exotic many-body quantum phases in a 2D platform made of pure carbon and without magnetic field. The easy accessibility of the flat bands, the electrical tunability, and the bandwidth tunability though twist angle may pave the way towards more exotic correlated systems, such as quantum spin liquids or correlated topological insulators.

### **CANCELLED** May 1 — "Understanding and Predicting Turbulent Transport in Tokamak Plasmas"

• Presenter: Anne White, MIT
• Host: Scott Parker
• View the presentation slides here.
• Abstract: In magnetically confined fusion plasmas like tokamaks, transport of heat and particles is dominated by turbulence. Turbulent transport models can be validated using experimental data, using a rigorous methodology and direct comparisons with turbulence measurements.  While the transport models capture details of the turbulence very well, and can be used to predict steady-state temperature profiles for ITER and SPARC and other future tokamaks, there remain several outstanding questions. A long-standing enigma in plasma transport consists of the observation that controlled edge cooling of fusion plasmas triggers core electron temperature increases on time scales faster than an energy confinement time, which has long been interpreted as strong evidence of nonlocal transport. A novel integrated modeling tool, that we call PRIMA, leverages the new trapped gyro-landau fluid transport (TGLF) model that includes multi-scale physics. This modeling tool has been used to interpret data from C-Mod and develop predictions for new experiments at DIII-D. The interpretive analysis at C-Mod shows that the steady-state profiles, the cold-pulse rise time, and the disappearance at higher density measured in these experiments are well matched by the new TGLF model. This provides new evidence that the existence of nonlocal transport phenomena is not necessary for explaining cold-pulse experiments in tokamak plasmas. Predictive analysis was used to design a new experiment to leverage the new Laser Blow-Off (LBO) system at DIII-D, to test whether or not cold pulse inversion will occur on DIII-D, and if it does occur, to test whether the model can accurately predict the plasma conditions where it occurs. Detailed interpretive and predictive analysis from the C-Mod and DIII-D tokamaks will be presented, to make the case that the existence of nonlocal transport phenomena is not necessary for explaining the behavior and time scales of cold-pulse experiments in tokamak plasmas. This work has helped improve confidence in predictive capabilities for ITER, SPARC and other future tokamak experiments.

For more information about colloquia this semester, contact: Mihaly Horanyi.

Colloquia are Wednesdays at 4:00 p.m. in DUAN G1B20, unless otherwise noted.

Coffee, tea and cookies will be available before regular colloquia beginning at 3:45 p.m. in DUAN G1B31.

### August 29 — "Tales from the Cold: New Science from Superconducting Sensors"

• Presenter: Joel Ullom, NIST Boulder
• Host: Scott Diddams
• Abstract: In the last decade, superconducting sensors operating at milliKelvin temperatures have evolved from laboratory curiosities to powerful tools for performing science.  These sensors are now essential for fields of science such as studies of the cosmic microwave background, and they are beginning to impact research areas previously thought unsuitable such as beamline science at large x-ray lightsources.  In this seminar, I will cover three interrelated topics: (1) the growing scope of application for superconducting sensors, (2) recent advances in performance enabled by better fundamental understanding of their behavior, and (3) some examples of recent science enabled by these devices, including demonstrations of tabletop ultrafast x-ray emission and absorption spectroscopy.  Timely background information is available in ref. 1.

[1] K. Morgan, Physics Today 71, 8, 28 (2018); doi: 10.1063/PT.3.3995

### September 5 — "Whispering-gallery-mode microresonators: fundamentals and applications"

• Presenter: Lan Yang, Washington University
• Host: Juliet Gopinath
• Abstract: Light-matter interactions are the fundamental basis for many phenomena and processes in optical devices. Whispering-Gallery-Mode (WGM) optical resonators trap light in a manner similar to a phenomenon found in the gallery spaces of St. Paul’s Cathedral dome in London, where a single whisper (i.e., a sound wave) can be heard along the circular boundary of the architecture. Ultra-high-quality WGM optical micro-resonators provide unprecedented capability to trap light in a highly confined volume smaller than a strand of human hair; a light beam can travel around the boundary of a WGM resonator over 106 times, significantly enhancing light-matter interactions, creating the potential for a wealth of new scientific discoveries and technological breakthroughs difficult to achieve by other devices. They have shown a great promise for a variety of fields of science, spanning from optomechanics to communication, non-Hermitian physics, sensing and metrology. In this talk, I will report the recent research discoveries from my group in this exciting field. I will present a few cases demonstrating the great potentials of high-Q WGM microresonators and microlasers for both fundamental science and engineering applications. Specifically, I will discuss ultra-high-Q microresonators and microlasers for ultra-sensitive detection of nanoscale objects. I will explain a self-referencing sensing scheme for detection and sizing of single virion, dielectric and metallic nanoparticles. These recent advancements in WGM microresonators will enable a new class of ultra-sensitive and low-power sensors for investigating the properties and kinetic behaviors of nanomaterials, nanostructures, and nanoscale phenomena. Afterwards, I will discuss our recent exploration of fundamental physics, such as parity-time symmetry (PT-symmetry) and light-matter interactions around exceptional points (EPs) in high-quality WGM resonators, which can be used to achieve a new generation of optical system enabling unconventional control of light flow. Examples including nonreciprocal light transmission, loss engineering in a lasing system, directional lasing emission, and EPs enhanced sensing, will be introduced. A non-Hermtian phonon laser tuned in the vicinity of EPs will be discussed briefly. In the end, I will present a new generic and hand-held microresonator platform transformed from a table-top setup, which will help release the power of high-Q WGM resonator technologies.

Short bio: Professor Lan Yang is the Edwin H. and Florence G. Skinner professor in the Preston M. Green Department of Electrical and Systems Engineering at Washington University, St. Louis, MO, USA. She received B.S. from the University of Science and Technology of China and received her Ph.D. in applied physics from Caltech in 2005. Her research interests have been focusing on the fundamental understanding of high-quality photonic whispering-gallery-mode (WGM) resonators and their applications for sensing, lasing, light harvesting, and communications. Recently, her research interests expanded to parity-time-symmetry and non-Hermitian physics in high-quality WGM resonators, which have led to a series of new discoveries for unconventional control of light transport in photonic structures. She received NSF CAREER Award in 2010 for her work on single nanoparticle detection and sizing using an on-chip optical resonator. She is also the recipient of the 2010 Presidential Early Career Award for Scientists and Engineers (PECASE). She is a fellow of the Optical Society of America (OSA).

### September 12 — "Picoastronomy: an electron microscopist's view of the history of the Solar System"

• Presenter: Rhonda Stroud, U.S. Naval Research Laboratory
• Host: Mihaly Horanyi
• Abstract: A wide range of astrophysical processes, from condensation of dust particles in circumstellar envelopes to space weathering on airless bodies, are inherently pico-to-nanoscale phenomena. Thus, an electron microscope, used for direct observation of planetary materials in the laboratory, can be as much of an astronomical tool as a telescope pointed at the sky. The energy resolution of state-of-the-art monochromated scanning transmission electron microscopes (STEMs), as low as 10 meV, makes it possible to directly observe the infra-red optical properties of individual cosmic dust grains in the 2 to 25 um range. Thus, distinguishing the 10-um and 18-um features of individual bonafide astrosilicates is now possible. Furthermore, the spatial resolution and sensitivity of the STEM enables imaging and at spectroscopy at scales down to the single atom. Samples of nanomaterials from diverse classes of stars from red giants to supernovae, from asteroids and comets, and the surface of the Moon are all available for laboratory studies. Results of these studies can help aid in the understanding of the formation and evolution of solar systems, and even provide clues for advancing the development of technologically important materials, such as doped nanodiamonds, SiC and graphene.

### September 19 — "Magnetism and spin in quantum materials"

• Presenter: Minhyea Lee, University of Colorado Boulder
• Host: John Cumalat
• Abstract: Quantum materials are crystalline solids with exotic physical properties arising from the quantum mechanical nature and interactions of electrons.  Quantum phenomena such as fluctuations, topology, tunneling and interference are at the heart of exciting developments in the fundamental science of quantum materials. At the same time, these phenomena have the potential to play a key role in future technologies.

In this colloquium I will give some examples from my research on magnetism, illustrating the discovery of novel phenomena in quantum materials, and the development of frameworks that can guide the search for new materials and devices with advanced functionality.

### September 26 — "Quantum Nanophotonics from Ultrathin Metallic Junctions"

• Presenter: Maiken Mikkelsen, Duke University
• Host: John Bohn
• Abstract: Tiny gaps between metals enables extreme field enhancements and strongly modified light-matter interactions promising for ultrafast optoelectronics, energy applications and on-chip components for quantum information processing. We use creative nanofabrication techniques at the interface between chemistry and physics to realize nanostructures with critical dimensions on the atomic- and molecular-scale (~1-10 nm), together with advanced, ultrafast optical techniques to probe the emerging phenomena. Here, I will provide an overview of our recent research demonstrating tailored light-matter interactions by leveraging ultra-small plasmonic cavities fabricated with bottom-up techniques. Examples of our demonstrations include 1,000-fold Purcell enhancements [Nature Photonics 8, 835 (2014)], ultrafast single photon sources [Nano Letters 16, 270 (2016)], tailored emission from two-dimensional semiconductor materials [Nano Letters 15, 3578 (2015), ACS Photonics 5, 552 (2018)], perfect absorbers and combinatorial plasmonic colors [Advanced Materials 27, 7897 (2015), Advanced Materials 29, 1602971 (2017)].

Bio:

Maiken H. Mikkelsen is the James N. and Elizabeth H. Barton Associate Professor at Duke University in the Departments of Physics, Electrical & Computer Engineering, and Mechanical Engineering & Materials Science. Currently, she is a Visiting Associate Professor at Stanford University in the Department of Materials Science & Engineering. She received her B.S. from the University of Copenhagen in 2004, her Ph.D. in Physics from the University of California, Santa Barbara in 2009 and was a postdoctoral fellow at the University of California, Berkeley. Her research focuses on nanophotonics and quantum materials to enable transformative breakthroughs for optoelectronics, the environment and human health. Her awards include the Maria Goeppert Mayer Award from the American Physical Society, the Early Career Achievement Award from SPIE, the NSF CAREER award, the Cottrell Scholar Award from the Research Corporation for Science Advancement and Young Investigator Program Awards from the ONR, ARO and AFOSR.

### October 3 — "The physics, biology, and technology of resonance energy transfer"

• Presenter: Philip Nelson, University of Pennsylvania
• Host: Loren Hough
• Abstract: Resonance energy transfer has become an indispensable experimental tool for single-molecule and single-cell biophysics, and a conceptual tool to understand bioluminescence and photosynthesis. Its physical underpinnings, however, are subtle: It involves a discrete jump of excitation from one molecule to another, and so we regard it as a strongly quantum-mechanical process. And yet its first-order kinetics differ from what many of us were taught about two-state quantum systems; quantum superpositions of the states do not seem to arise; and so on. The key step involves acknowledging quantum decoherence.

Ref: P C Nelson, Biophys J 115: 167(2018) http://doi.org/10.1016/j.bpj.2018.01.010

### October 10 — "Front and center: physics and the large size of whales"

• Presenter: Jean Potvin, Saint Louis University
• Host: Tom DeGrand
• Abstract: Large baleen whales such as the humpback and blue whales have become the shining stars of a great number of popular nature documentaries. Paradoxically, much of their physiology remains poorly understood. Generally one must look into a complex web of relationships between morphology, physiology, ecology and bio-mechanics to explain the whys and hows of, for example, body architecture. In this presentation I show that the blue whales and their baleen-bearing cousins represent shining examples of the central role played by physics in shaping their evolution into the largest and most massive life forms to have ever lived on Earth. The peculiarities of their feeding strategies permit the use of simple formulations of the work-energy and momentum conservation principles to estimate swimming metabolic energetic expenditures over size and demonstrate how body gigantism can not only become an advantage but also a disadvantage. This presentation will also show the results of an ongoing NSF-funded and inter-disciplinary study aimed at collecting kinematic and video data on humpback and blue whales foraging off the coast of California, with the goals of further understanding their feeding behavior as well as providing data for physical modeling validation.

### October 17 — "Observing quantum materials in real time by pump-probe Raman Scattering"

• Presenter: Dmitry Reznik, University of Colorado Boulder
• Host: Mihaly Horanyi
• Abstract: Pump-probe experiments open a completely new way to study and control quantum materials. Their behavior away from thermal equilibrium, generation of metastable phases, photoexcited states, quantum computing-related phenomena, chemical reactions, energy dissipation, etc. can now be measured in real time with unprecedented precision due to rapid advances in ultrafast lasers and x-ray sources. In this talk I will give an overview of several representative pump-probe techniques and then focus on time-resolved Raman scattering. I will then discuss a demonstration project elucidating how energy from hot electrons cascades through different vibrational modes on the way to the thermal bath in graphite. Finally, to illustrate the diversity of problems that can be addressed, I will show how pump-probe Raman scattering is used to probe relaxation of the magnetic state in an antiferromagnetic Mott insulator.

### October 24 — "From the Big Bang to Signs of Alien Life, with the James Webb and Future Telescopes"

• Presenter: John Mather, Goddard Space Flight Center
• Host: Jason Glenn
• Abstract: Planned for launch in 2021 on an Ariane 5 from French Guiana, the James Webb Space Telescope (JWST) will observe at wavelengths from 0.6 to 28 µm with a full suite of imagers, spectrometers, and coronagraphs. JWST will extend the discoveries of the Hubble and Spitzer observatories in all areas from cosmology, galaxies, stars, and exoplanets to our own Solar System. With a 6.5 m primary mirror it has a collecting area 7 times that of Hubble and 50 times that of Spitzer. Inventions were required ranging from deployment and in-flight focusing of its segmented telescope, to greatly improved infrared detectors, to a 6 Kelvin refrigerator for one of the instruments.  I will outline the planned observing program and the major scientific challenges being addressed. What were the first objects that formed in the expanding universe? How do the galaxies grow? How are black holes made, ranging from stellar mass to supermassive, over a billion solar masses, and what is their effect on the neighborhood? How are stars and planetary system formed? What governs the evolution of planetary systems, with the possibility of life? How did the Earth become so special? But the most important discoveries will be those we have not even imagined today.

I will also describe the new telescopes being built on the ground and proposed for space, ranging from far infrared to X-rays.  And now for something completely different, I am developing a radical idea to observe exoplanets with ground-based telescopes and extreme adaptive optics, using an orbiting starshade. Since it does not require a space telescope, it could reveal an Earth twin with signs of life within the next 15 years. Not easy, but not impossible!

### October 31 — "Searching beyond the Standard Model at the LHC"

• Presenter: Kevin Stenson, University of Colorado Boulder
• Host: John Cumalat
• Abstract: With the discovery of the Higgs boson in 2012 by the CMS and ATLAS collaborations, all of the fundamental particles in the standard model of particle physics have been observed.  Nevertheless, the many open questions in particle physics make it clear that the Standard Model is not a complete theory, and the main goal now is to discover what lies beyond the Standard Model.  I will describe some existing searches from the CMS experiment at the LHC and how the accelerator and detectors will be upgraded over the next decade to increase our sensitivity to new phenomena.

### November 14 — "Active Matter: from colloids to living cells"

• Presenter: M. Cristina Marchetti, University of California, Santa Barbara
• Host: Leo Radzihovsky
• Abstract: Collections of self-propelled entities, from living cells to engineered microswimmers, organize in a rich variety of active fluid and solid states, with unusual properties. For instance, active fluids can flow with no externally applied driving forces and active gases do not fill their container. In this talk I will describe the behavior of such “active materials” and highlight two examples of active phase transitions. The first is the formation of cohesive matter with no cohesive forces in collections of purely repulsive active colloids. The second is a model of epithelial tissues that exhibit a liquid-solid transition at constant density driven by cell motility, contractility, and cell-cell adhesion.

### November 28 — "Nanoscale Lasing: A Conundrum?"

• Presenter: Teri Odom, Northwestern University
• Host: Scott Diddams
• Abstract: Metal nanostructures concentrate optical fields into highly confined, nanoscale volumes that can be exploited in a wide range of applications. However, the use of plasmonic structures as cavities for generating coherent emission seems counter-intuitive based on conventional designs of macroscopic lasers. This talk will describe how arrays of nanoparticles can support a unique open-cavity architecture that can be used to interrogate the mechanisms of energy transfer processes and plasmon amplification in confined systems. First, we will describe how single band-edge lattice plasmons in metal nanoparticle arrays can contribute to single-mode lasing at room-temperature with directional emission. Second, we will discuss how ultra-narrow resonances from superlattice plasmons, collective excitations in hierarchical nanoparticle arrays, can support multi-modal nanolasing. Finally, we will describe challenges in and approaches to differentiating among competing energy transfer in the lasing action based on coherence, cavity size, and ultra-fast characteristics.
• Biography: Teri W. Odom is Charles E. and Emma H. Morrison Professor of Chemistry and Chair of the Chemistry Department at Northwestern University. She is an expert in designing structured nanoscale materials that exhibit extraordinary size and shape-dependent optical properties. Odom has pioneered a suite of multi-scale nanofabrication tools that has resulted in flat optics that can manipulate light at the nanoscale and beat the diffraction limit, plasmon-based nanoscale lasers that exhibit tunable color, and hierarchical substrates that show controlled wetting and super-hydrophobicity. She has also invented a class of biological nanoconstructs that are facilitating unique insight into nanoparticle-cell interactions and that show superior imaging and therapeutic properties because of their gold nanostar shape.

Odom is a Fellow of the American Physical Society (APS), the American Chemical Society (ACS), the Materials Research Society (MRS), the Optical Society of America (OSA), the Royal Society of Chemistry (RSC), and is an OSA Senior Member. She has received numerous other honors and awards, including a Research Corporation TREE Award; a U.S. Department of Defense Vannevar Bush Faculty Fellowship; the Associated Student Government Faculty Honor Roll; the Carol Tyler Award from the International Precious Metals Institute; a Blavatnik Young Scientist Finalist in Chemistry and Physical Sciences and Engineering; a Radcliffe Institute for Advanced Study Fellowship at Harvard University; the ACS Akron Section Award; an National Institutes of Health (NIH) Director's Pioneer Award; the MRS Outstanding Young Investigator Award; the National Fresenius Award from Phi Lambda Upsilon and the ACS; the Rohm and Haas New Faculty Award; an Alfred P. Sloan Research Fellowship; a DuPont Young Investigator Grant; a NSF CAREER Award; the ExxonMobil Solid State Chemistry Faculty Fellowship; and a David and Lucile Packard Fellowship in Science and Engineering. Odom was founding Chair of the Noble Metal Nanoparticles Gordon Research Conference (2010) and founding Vice-Chair of Lasers in Micro, Nano, Bio Systems (2018). She is on the Editorial Advisory Boards of ACS Nano, Materials Horizons, Annual Reviews of Physical Chemistry, ChemNanoMat, Chemical Society Reviews, Bioconjugate Chemistry, and Nano Letters. She was founding Associate Editor for Chemical Science (2009-2013) and serves as founding Executive Editor of ACS Photonics (2013 - ). Odom’s Personal Story of Discovery was featured by ACS Publications.

### **Special Colloquium: Monday, December 3** — "An Introduction to Quantitative Finance from the Viewpoint of an Experimental Physicist"

• Presenter: Joseph Mitchell, former researcher at Renaissance Technologies
• NOTE SPECIAL LOCATION: DUAN G125
• Host: Jerry Peterson
• Abstract: During the past several decades it has become common for Wall Street firms to hire workers trained in Physics, Mathematics and other technical fields. Given this, it is perhaps interesting for physicist to learn a bit about quantitative finance. We will discuss some properties of financial data and the very basics of risk and cost models. Along the way we will contrast some aspects of financial data analysis with the data analysis of physics experiments. Finally, time permitting, we will discuss a textbook example of a trading strategy.

### December 5 — "Watching Chemical Reactions Happen One Molecule at a Time"

• Presenter: Heather Lewandowski, JILA, Department of Physics, University of Colorado Boulder
• Host: John Cumalat
• Abstract: Reactions between ions and radical molecules play an important role in the chemistry that drives dynamics in the interstellar medium and during combustion of hydrocarbons. Unfortunately, experimental measurements of these reactions are very challenging, and thus very rare. We use tools borrowed from the cold atom community to measure ion-molecule reactions in a well-controlled environment. Here, we can study reactions between atoms and molecules in single quantum states at low temperatures. Our high sensitivity allows us to study reactions where the reaction rate can be as low as one reaction per minute. I will present the capabilities of this cold ion-molecule reaction apparatus and some example reactions we have been able to study using this new system.

### December 12 — "Mixed Conduction in Polymeric Materials: Electrochemical devices for Biosensing and Neuromorphic Computing"

• Presenter: Alberto Salleo, Stanford University
• Host: Sean Shaheen
• Abstract: Organic semiconductors have been traditionally developed for making low-cost and flexible transistors, solar cells and light-emitting diodes. In the last few years, emerging applications in health case and bioelectronics have been proposed. A particularly interesting class of materials in this application area takes advantage of mixed ionic and electronic conduction in certain semiconducting polymers. Indeed, the ability to transduce ionic fluxes into electrical currents is useful when interacting with living matter or bodily fluids. My presentation will first discuss the fundamental aspects of how mixed conduction works in polymeric materials and then focus on two families of devices made with such materials: electrochemical transistors and artificial synapses.
1- Biosensing using electrochemical transistors: The continuous monitoring of human health can greatly benefit from devices that can be worn comfortably or seamlessly integrated in household objects, constituting “health-centered” home automation aka "domotics". I will describe electrochemical transistors that detect ionic species either directly present in body fluids or resulting from a selective enzymatic reaction (e.g. ammonia from creatinine) at physiological levels. Additionally, I will show that non-charged molecules can be detected by making use of custom-processed polymer membranes that act as “synthetic enzymes”. Using these membranes in conjunction with electrochemical transistors we demonstrate that we are able to measure physiological levels of cortisol in real human sweat. Finally, I will show a more biomimetic approach where the sensing layer is a lipid membrane stabilized at a liquid-liquid interface, which we use to detect antimicrobial compounds. The same basic device that we use for sensing can also be used for computing.
2- Polymer-based artificial synapses: The brain can perform massively parallel information processing while consuming only ~1 - 100 fJ per synaptic event. I will describe a novel electrochemical neuromorphic device that switches at record-low energy (<0.1 fJ projected, <10 pJ measured) and voltage (< 1 mV, measured), displays >500 distinct, non-volatile conductance states within a ~1 V operating range. Furthermore, it achieves record classification accuracy when implemented in neural network simulations. Our organic neuromorphic device works by combining ionic (protonic) and electronic conduction and is essentially similar to a concentration battery. The main advantage of this device is that the barrier for state retention is decoupled from the barrier for changing states, allowing for the extremely low switching voltages while maintaining non-volatility. I will show that the device can rival commercial flash memory in terms of endurance and possibly switching time. When accessed with an appropriate switching device it exhibits excellent linearity, which is an important consideration for neural networks that learn with blind updates.
Speaker Bio: Alberto Salleo is currently an Associate Professor of Materials Science at Stanford University. Alberto Salleo holds a Laurea degree in Chemistry from La Sapienza and graduated as a Fulbright Fellow with a PhD in Materials Science from UC Berkeley in 2001. From 2001 to 2005 Salleo was first post-doctoral research fellow and successively member of research staff at Xerox Palo Alto Research Center. In 2005 Salleo joined the Materials Science and Engineering Department at Stanford as an Assistant Professor and was promoted to Associate Professor in 2013. Salleo is a Principal Editor of MRS Communications since 2011.While at Stanford, Salleo won the NSF Career Award, the 3M Untenured Faculty Award, the SPIE Early Career Award, the Tau Beta Pi Excellence in Undergraduate Teaching Award, and the Gores Award for Excellence in Teaching, Stanford’s highest teaching award. He has been a Thomson Reuters Highly Cited Researcher since 2015, recognizing that he ranks in the top 1% cited researchers in his field.

For more information about colloquia this semester, contact: Mihaly Horanyi.

Colloquia are Wednesdays at 4:00 p.m. in DUAN G1B20, unless otherwise noted.

Coffee, tea and cookies will be available before regular colloquia beginning at 3:45 p.m. in DUAN G1B31.

### January 17 — "Can Evolutionary Dynamics Be Understood Quantitatively?"

• Presenter: Daniel Fisher, Stanford University
• Host: Leo Radzihovsky
• Abstract: The basic laws of evolution have been known for more than a century and there is overwhelming evidence for the facts of evolution. Yet little is understood quantitatively about the dynamical processes that drive evolution: by physicists' standards the theory of evolution is far from fully-fledged. Huge advances in DNA sequencing technology and laboratory experiments have enabled direct observations of evolution in action and, together with theoretical developments, opened up great opportunities for dramatically advancing our understanding. This talk will focus on framing questions and on recent progress addressing some of these.

### January 24 — "Zen and the Art of Atomic Physics"

• Presenter: Eric Hudson, University of California, Los Angeles
• Host: John Bohn
• Abstract: In the Ten Bulls tradition, the fifth stage of Zen is reached when the practitioner has caught and tamed the wild bull. This is roughly the state of atomic physics. The atom has been tamed. It can be prepared in a single quantum state, its evolution coherently controlled, and its entanglement generated at will.  As such, many new quantum-assisted technologies and fundamental physics measurements have resulted and a quantum revolution is well underway that promises to touch almost every aspect of our lives. By the seventh stage of Zen, the Bull has transcended and is no more. This again may be paralleled in atomic physics as the atom is being replaced with richer quantum systems such as molecules, whose internal degrees of freedom provide new opportunities for quantum science and technology.
In this talk, I will briefly review the science and technology that have come from atom taming and then discuss our efforts to tame other bulls: polar molecular ions and atomic nuclei.

### January 31 — "Exploring the Ocean Worlds of the Outer Solar System for Life"

• Presenter: Jonathan Lunine, Cornell University
• Host: Sascha Kempf
• Abstract: Planetary exploration of the Jovian and Saturnian systems has revealed that three moons—Europa, Titan and Enceladus-- have either liquid water oceans or, for Titan, seas of hydrocarbons that are potentially interesting abodes for life. I will describe what we know of these bodies, in what way we think they are habitable, and a strategy to determine if life is present on any or all of them.

### January 31 — "Exploring the Ocean Worlds of the Outer Solar System for Life"

• Presenter: Jonathan Lunine, Cornell University
• Host: Sascha Kempf
• Abstract: Planetary exploration of the Jovian and Saturnian systems has revealed that three moons—Europa, Titan and Enceladus-- have either liquid water oceans or, for Titan, seas of hydrocarbons that are potentially interesting abodes for life. I will describe what we know of these bodies, in what way we think they are habitable, and a strategy to determine if life is present on any or all of them.

### February 7 — "Dirac, Jordan, and von Neumann: Hilbert space and transformation theory"

• Presenter: Michel Janssen, University of Minnesota
• Host: Allan Franklin
• Abstract: In early 1927, Paul Dirac and Pascual Jordan, independently of one another, published their versions of a general formalism tying the various forms of the new quantum theory together and giving the theory's statistical interpretation in full generality. This formalism has come to be known as the Dirac-Jordan (statistical) transformation theory. A few months later, in response to these publications by Dirac and Jordan, John von Neumann published his Hilbert space formalism for quantum mechanics. The relation between the two formalisms can be captured in terms of a metaphor of arches and scaffolds that I have argued fits a number of instances of theory change in physics. What is unclear in this case is whether the story is best told with Hilbert space playing the role of the arch built on transformation theory as a scaffold to be dismantled once the arch could support itself, or with transformation theory playing the role of the arch and Hilbert space providing the scaffold built to prevent the arch from collapsing under the weight of its serious mathematical deficiencies. Either way, a narrative for this episode in the history of quantum mechanics based on the arches-and-scaffolds metaphor illustrates the promise of borrowing ideas from the approach to evolutionary biology known as evodevo for reconstructing genealogies of theories rather than species.

### **Special Physics Faculty Candidate Search Colloquium** Thursday, February 8 — "Exploring the hydrodynamic limit of many-body quantum systems"

• Presenter: Andrew Lucas, Harvard University
• Location and time: JILA X317, 4:00 p.m
• Host: Paul Romatschke
• Abstract: The emergence of hydrodynamics in complicated microscopic many-body models has been a problem of interest in physics for more than a century. I will describe two ways that the classical theory of hydrodynamics is still teaching us interesting things about interacting many-body quantum systems. Firstly, I will derive the constraints relating classical hydrodynamic phenomena to the spreading of quantum information. These bounds sharpen and clarify many previous conjectures on whether quantum fluids have the smallest diffusion constants allowed in nature. I will briefly outline how an exotic class of quantum systems, which are holographically dual to a black hole in one higher dimension, serve as highly non-trivial checks on these diffusion bounds. Secondly, I will describe hydrodynamic theories of transport in metals. Even though measuring the thermal and electrical conductivity of a metal is very easy experimentally, conventional approaches to transport theory are not adequate for metals where the electronic interactions are strong. I will describe recent experimental evidence for hydrodynamic transport, including dramatic violations of the Wiedemann-Franz law, and present a new mechanism for electron-limited transport, possibly applicable to single-band materials including SrTiO3.

### **Special Physics Faculty Candidate Search Colloquium** Monday, February 12 — "How low can the energy density go?"

• Presenter: Aaron Wall, University of Maryland
• Location: DUAN G125
• Host: Paul Romatschke
• Abstract: Quantum fields can sometimes have negative energy density.  In gravitational contexts, this threatens to permit both causality violations (such as traversable wormholes, warp drives, and time machines) and violations of the Second Law for black holes.  I will discuss the thermodynamic principles that rule out such pathological situations.  These principles have led us to an interesting lower bound on the energy flux, even for field theories in flat spacetime!
This Quantum Null Energy Condition has recently been proven for general relativistic field theories.  I will give an intuitive argument explaining why such quantum energy conditions'' ought to hold.

### February 14 — "Who ordered that: what lepton flavor may tell us about the Universe"

• Presenter: Yury G. Kolomensky, University of California, Berkeley
• Host: Eric Zimmerman
• Abstract: Muons, heavy cousins of electrons whose existence famously puzzled I.I. Rabi, may play an important role in understanding the behavior of particles and fields at the highest energies. Searches for transitions that violate the apparent lepton flavor conservation are sensitive to new interactions with the energy scale above those accessible in the modern colliders. Recent hints of deviations from the Standard Model expectations in the processes involving muons are intriguing, and motivate new measurements over the next decade. Among those, the Mu2e experiment at Fermilab will search for neutrinoless muon-to-electron conversion with unprecedented precision. I will discuss the history of the lepton flavor measurements, and describe the design and present status of Mu2e, which will improve the current constraints by four orders of magnitude.

### **Special Physics Faculty Candidate Search Colloquium** Thursday, February 15 — "Sources of student interest and engagement in Introductory Physics for Life Science"

• Presenter: Ben Geller
• Location: JILA Auditorium
• Time: 3:00 - 4:00 p.m.
• Host: Heather Lewandowski
• Abstract:  Effectively teaching an Introductory Physics for Life Science (IPLS) course means engaging life science students in a subject for which they may not have considerable preexisting interest. We have found that the inclusion of topical examples of relevance to life-science students can help to engage students whose initial interest in physics is less developed, but that different examples and models vary in their effectiveness. Examples that ground physical models in authentic biological and biochemical contexts with which the students are already familiar, and about which they may already have authentic driving questions, are especially effective. By analyzing data from (1) survey instruments assessing student attitudes and interest in particular life science examples, and (2) interviews conducted with students before and after instruction, we identify features of our IPLS course that appear to be particularly important for fostering student learning and engagement. We suggest that some of these features might also foster student interest in more traditional introductory physics courses.

### **Special Physics Faculty Candidate Search Colloquium** Thursday, February 15 — "Holographic phase diagrams"

• Presenter: Christiana Pantelidou, Imperial
• Location: JILA X317
• Host: Paul Romatschke
• Abstract: Over the last 20 years, the Gauge/Gravity correspondence has led to significant progress in the understanding of strongly coupled matter without quasiparticles, found both in Condensed Matter systems and Quantum Chromodynamics. In this talk, after an extended pedagogical introduction on the subject, I will discuss the various phases that have been discovered using this approach, how they compete with each other and what is currently known about their ground states.

### **Special Physics Faculty Candidate Search Colloquium** Monday, February 19 — "The atoms of an expanding universe"

• Presenter: Dionysios Anninos, Harvard University
• Location: DUAN G125
• Host: Paul Romatschke
• Abstract: Observations over the past few decades have provided important evidence about the geometry of the large-scale universe.
During the early inflationary era, as well as the current vacuum dominated era, the evidence points to a universe described by an exponentially expanding de Sitter spacetime. From the perspective of theoretical physics, the last two decades have seen remarkable progress in our understanding of spacetime as an emergent, collective phenomenon stemming from a microscopic holographic system with a large number of atomic' constituents. This has been achieved with great success for negatively curved anti-de Sitter spacetimes. We will explore holography for a de Sitter universe. Our discussion will be guided by the construction and consideration of concrete mathematical models, providing an exact realization of the dS-CFT correspondence.
We will also discuss similarities and distinctions between the cosmological horizon of a de Sitter universe and the horizon of an ordinary black hole from a modern, holographic perspective.

### February 21 — "Superconducting Microresonators: From Astrophysics to Zero-Point Fluctuations"

• Presenter: Jonas Zmuidzinas, Caltech
• Host: Jason Glenn
• Abstract: The hallmark of superconductivity – zero electrical resistance – explains why superconducting resonators can have very low dissipation (high Q). Superconducting resonators at the macro scale have been developed for decades and enable energy-efficient high-energy accelerators such as the LHC. At the micro scale, superconducting resonators have attracted considerable attention in recent years and are being applied to a rapidly growing range of applications, from photon detectors for astrophysics to quantum circuits. This presentation will describe the advances in superconducting microresonators over the past two decades, focusing on their use as detectors and the relevant physical phenomena, but including a wide variety of other applications.

### February 28 — "Command of Swimming Bacteria by Liquid Crystals"

• Presenter: Oleg Lavrentovich, Kent State University
• Host: Joe MacLennan
• Abstract: Self-propelled bacteria are marvels of nature. If we can control their dynamics, we could use it to power microsystems of the future. Unfortunately, bacteria swim mostly randomly in isotropic liquids such as water. It is difficult to control their dynamics by factors other than transient gradients of nutrients; visual, acoustic and tactile communication channels that humans use to control large animals are not effective. To establish communication, we replace water with a water-based lyotropic liquid crystal, which couples propulsion of bacteria to the orientational order of the medium. The long-range orientational order of the liquid crystal can be designed as uniform or be pre-patterned into various structures by a plasmonic photoalignment technique [1]. The preimposed patterns of liquid crystal orientation allow one to gain a significant control over the dynamics of bacteria, namely, their trajectories, polarity of swimming, spatial variation of concentration [2], and run-and-tumble behavior [3]. Topological defects of integer strength serve either as attractors or repellents of bacteria, while defect pairs and patterns with broken left-right symmetry pump the bacterial flows along a preselected polar axis. The study of bacteria-liquid crystal system might result in approaches to harness the energy of collective motion for micro-robotic, biomechanical, and sensing devices, as well as micro-mixing and transport of micro-cargo. The work is supported by NSF grants DMR-1507637 and DMS-1729509.

### March 7 — "EPR and spatial-mode entanglement in spinor Bose-Einstein condensates"

• Presenter: Carsten Kempt, Institut für Quantenoptik, Leibniz Universität Hannover
• Host: Ana Maria Rey
• Abstract: Spin changing collisions in alkaline Bose-Einstein condensates can be employed to generate highly entangled atomic quantum states. Here, we will report on the generation of two classes of entangled states. Firstly, we demonstrate the generation of two-mode squeezed vacuum states and record their characteristic quadrature correlations by atomic homodyning. We prove that the correlations fulfill Reid’s criterion [1] for continuous-variable Einstein-Podolsky-Rosen entanglement. The homodyne measurements allow for a full tomographic reconstruction, yielding a two-mode squeezed state with a 78% fidelity. The created state can be directly applied to atom interferometry, as is exemplified by an atomic clock measurement beyond the Standard Quantum Limit.
Secondly, we demonstrate entanglement between two spatially separated atomic modes. The entangled state is obtained by spatially splitting a Twin Fock state of indistinguishable atoms. The method opens a path to exploit the recent success in the creation of many-particle entanglement in ultracold atoms for the field of quantum information, where individually addressable subsystems are required. Finally, we will show how the measurement protocol can be extended to perform a Bell test of quantum nonlocality.

[1] M. Reid, Phys. Rev. A 40, 913–923 (1989)

### March 14 — "Throwing God's Dice"

• Presenter: Krister Shalm, NIST
• Host: John Price
• Abstract: In 1943 Einstein wrote to Max Born saying “As I have said so many times, God doesn't play dice with the world.” This discussion with Born was just one part of a much large debate on the consequences of quantum theory on the nature of reality. In 1935 Einstein, Podolsky, and Rosen famously published a paper with the aim of showing that the wave function in quantum mechanics does not provide a complete description of reality. The gedanken experiment showed that quantum theory, as interpreted by Niels Bohr, leads to situations where distant particles, each with their own “elements of reality”, could instantaneously affect one another. Such action at a distance seemingly conflicts with relativity. The hope was that a local theory of quantum mechanics could be developed where individual particles are governed by elements of reality, even if these elements are hidden from us. In such a theory, now known as local realism, these elements of reality or hidden variables could remove the randomness inherent in quantum mechanics.
In 1964 John Bell in a startling result showed that the predictions of quantum mechanics are fundamentally incompatible with any local realistic theory. In other words, an experiment can be done that can rule out all theories based on local hidden variables. Carrying out this test has been technologically challenging. It wasn’t until 2015 when three independent groups were able to rule out local realism in experiments free of loopholes. In this talk I will discuss the loophole-free Bell test carried out at the National Institute of Standards and Technology. I will also discuss how we can use such a Bell test to build a random number generator that can be certified by quantum mechanics itself. Such a random number generator that can trace its roots back to the original Einstein thought experiments is the closest we can get to “throwing God’s dice.”

### March 21 — "Exploring the 3D Nano and Atomic World: Coherent Diffractive Imaging and Atomic Electron Tomography"

• Presenter: John Miao, Deputy Director, NSF STROBE Science and Technology Center, Department of Physics and Astronomy and California NanoSystems Institute, University of California Los Angeles
• Host: Margaret Murnane
• Abstract: The discovery and analysis of X-ray diffraction from crystals by Max von Laue, William Henry Bragg and William Lawrence Bragg in 1912 marked the birth of crystallography. Over the last century, crystallography has been fundamental to the development of many fields of science. However, many samples in physics, chemistry, materials science, nanoscience, geology, and biology are non-crystalline, and thus their 3D structures are not accessible by traditional crystallography. Overcoming this major hurdle has required the development of new structure determination methods. In this talk, I will present two methods that can go beyond crystallography: coherent diffractive imaging (CDI) and atomic electron tomography (AET). In CDI, the diffraction pattern of a non-crystalline sample or a nanocrystal is first measured and then directly phased to obtain an image. The well-known phase problem is solved by combining the oversampling method with iterative algorithms. In the first part of the talk, I will illustrate several prominent CDI methods and highlight some important applications using high harmonic generation, 3rd generation synchrotron radiation and X-ray free electron lasers. In the second part of the talk, I will present a general tomographic method, termed AET, for 3D structure determination of crystal defects and disordered materials at atomic resolution. By combining advanced electron microscopes with novel data analysis and powerful computational algorithms, AET has been used to reveal the 3D atomic structure of crystal defects and chemical order/disorder, and to precisely localize the 3D coordinates of individual atoms in materials without assumption of crystallinity. The experimentally measured coordinates can then be used as direct input for quantum mechanical calculations of physical properties such as atomic spin and orbital magnetic moments and local magnetocrystalline anisotropy at the single-atom level. As large-scale and tabletop coherent X-ray sources and powerful electron microscopes are under rapid development worldwide, CDI and AET are expected to find broad applications in both the physical and biological sciences.
1.    J. Miao, T. Ishikawa, I. K. Robinson and M. M. Murnane, “Beyond crystallography: Diffractive imaging using coherent x-ray light sources”, Science 348, 530-535 (2015). (Review)
2.    J. Miao, P. Ercius and S. J. L. Billinge, "Atomic electron tomography: 3D structures without crystals", Science 353, aaf2157 (2016). (Review)
3.    Y. Yang, C.-C. Chen, M. C. Scott, C. Ophus, R. Xu, A. Pryor Jr, L. Wu, F. Sun, W. Theis, J. Zhou, M. Eisenbach, P. R. C. Kent, R. F. Sabirianov, H. Zeng, P. Ercius and J. Miao, “Deciphering chemical order/disorder and material properties at the single-atom level”, Nature 542, 75-79 (2017).

### April 4 — "Quantum-limited measurements: One physicist's crooked path from quantum optics to quantum information"

• Presenter: Carlton Caves, University of New Mexico
• Host: Scott Diddams
• Abstract: Quantum information science has changed our view of quantum mechanics. Originally viewed as a nag, whose uncertainty principles restrict what we can do, quantum mechanics is now seen as a liberator, allowing us to do things, such as secure key distribution and efficient computations, that could not be done in the realistic world of classical physics. Yet there is one area, that of quantum limits on high-precision measurements, where the two faces of quantum mechanics remain locked in battle. I will trace the history of quantum-limited measurements, from the use of nonclassical light to improve the phase sensitivity of an interferometer, to the modern perspective on the role of entanglement in improving measurement precision.

### April 11 — "From the Einstein-Bohr debate to quantum information: the second quantum revolution"

• Presenter: Alain Aspect, Institut d’Optique Graduate School, Palaiseau
• Host: Jun Ye
• Abstract: In 1935, with co-authors Podolsky and Rosen, Einstein discovered a weird quantum situation, in which particles in a pair are so strongly correlated that Schrödinger called them “entangled”. By analyzing that situation, Einstein concluded that the quantum formalism is incomplete. Niels Bohr immediately opposed that conclusion, and the debate lasted until the death of these two giants of physics.
In 1964, John Bell discovered that it is possible to settle the debate experimentally, by testing the now celebrated "Bell's inequalities", and to show directly that the revolutionary concept of entanglement is indeed a reality. A long series of experiments, started in 1972, have produced more and more precise results, in situations closer and closer to the ideal theoretical scheme.
After explaining the debate, and describing some experiments, I will show how this conceptual discussion has prompted the emergence of the new field of quantum information, at the heart of the second quantum revolution.

### **Special Physics Faculty Candidate Search Colloquium** Tuesday, April 17 — "Polarization in spectral lines: a window into the physics of the solar atmosphere"

• Presenter: Ivan Milić, Max Planck Institute for Solar System Research
• Location and time: JILA Auditorium, 4:00 p.m
• Host: Dmitri Uzdensky
• Abstract: The light that we receive from the Sun has passed through the solar atmosphere and undergone many scattering processes that leave their imprint on its spectral distribution and polarization state. These processes are influenced by the thermodynamic and magnetic properties of the plasma and thus the spectropolarimetric observations in spectral lines allow us to infer the temperature, velocity and magnetic field throughout the solar atmosphere.
This talk will focus on the Zeeman effect, scattering polarization and the Hanle effect, and how they contribute to form line polarization patterns. More specifically, the emphasis will be on spectral lines formed in non-local thermodynamic equilibrium conditions. Such lines typically probe the physical conditions in the upper layers of solar atmosphere, regions that are particularly interesting for their highly dynamic and magnetic nature. The diagnostic techniques, however, can be extended to a multitude of astrophysical objects, such as atmospheres of other stars and different types of accretion or circumstellar disks.
We will also discuss spectropolarimetric inversions, as the state-of-the-art tools used for the interpretation of the solar observations with high angular and spectral resolution. Finally, a brief outlook on the bright future of the field, especially in the light of Daniel K. Inouye Solar Telescope, will be presented.
Image: Observed intensity and circular polarization (top two panels), and inferred temperature, line-of-sight velocity and line-of-sight magnetic field at two different depths in an observed patch of the solar atmosphere.

### April 18 — "Optical atomic clock: a case study for the quantum technology revolution"

• Presenter: Jun Ye, JILA, University of Colorado Boulder
• Host: John Price
• Abstract: Precise quantum state engineering of individual atoms has led to the unprecedented measurement performance for time and frequency. The use of many atoms not only enhances the counting statistics, but is also emerging as a powerful tool to protect against systematic uncertainties. At the core of the new JILA three-dimensional optical lattice clock is a quantum gas of fermionic atoms that are spatially correlated to guard against motional and collisional effects.  The convolution of precision control of light and matter is helping bridge different disciplines in physics and fostering new capabilities to probe fundamental and emerging phenomena.

### **Special Colloquium** Wednesday, April 25 — "Driven Phases of Many-Body Quantum Matter"

• Presenter: Vedika Khemani, Harvard University
• Location and time: JILA Auditorium, 12:00 p.m
• Host: Leo Radzihovsky
• Abstract: Recent years have witnessed a remarkable confluence of diverse areas of physics coming together to inform fundamental questions about many-body quantum matter. A unifying theme in this enterprise has been the study of many-body quantum dynamics in systems ranging from electrons in solids to cold atomic gases to black holes.  One of the foundational pillars in the study of many-body systems is the theory of equilibrium statistical mechanics characterized by two fundamental ideas: thermalization (that interacting systems generically approach thermal equilibrium at late times) and phase structure (that equilibrium states of matter can display various forms of order separated by sharp phase transitions).

Recent progress, particularly in the field of many-body localization, has led to generalizations of these fundamental ideas to the out-of-equilibrium setting. I will describe this progress, particularly as applied to periodically driven or Floquet systems. I will show that not only can non-equilibrium systems exhibit a sharp notion of phase structure, but that some of these phases are completely novel and unique to the out-of-equilibrium setting. For example, certain phases of matter that are forbidden in equilibrium, such as quantum time crystals, have found new life in the out-of-equilibrium setting.  I will describe some of the many fascinating properties of this phase, and comment on recent experiments that have detected signatures of time crystals in a variety of different physical settings.

### April 25 — "Hot tips for thermal nanophysics"

• Presenter: Fabian Menges, University of Colorado, Boulder
• Host: John Price
• Abstract: Temperature is one of the most central concepts of thermal physics with historical roots in the seventeenth century mechanics and nineteenth century thermodynamics. Building up on these early foundations, I will highlight how the understanding of temperature gets increasingly challenging when small systems are away from equilibrium, get scaled to ensemble sizes below classical limits, and when quantum effects become relevant. Today, the apparently simply question of ‘what is the temperature’ is again up for debate, fueled by the miniaturization of technology and the experimental progress to study physical properties and processes down to atomic length and ultrafast time scales. Aiming to clarify questions such as how to measure temperature on the length-scale of nanoscale transistors, how interfaces and contacts influence dissipation processes, and how fundamental heat and charge transport relations may change at the atomic scale, we have recently developed new thermal nanometrology techniques based on scanning probe methods [1]. By demonstrating the real-space quantification of local Joule and Peltier effects at metal-semiconductor contacts [2], and the first atomic scale validation of the Wiedemann-Franz law at room temperature [3], I will illustrate the application of these approaches. Finally, I’ll provide an outlook on our ongoing efforts to open the door for spatio-temporal characterization of thermal phenomena at the transition from the classical to the quantum regime.

References:

[1] F. Menges et al., Nanoscale thermometry by scanning thermal microscopy, Review of Scientific Instruments (87) 7, 074902, 2016.

[2] F. Menges et al., Temperature mapping of operating nanoscale devices by scanning probe thermometry, Nature Communications 7(10874), 2016.

[3] N. Mosso et al., Heat transport through atomic contacts, Nature Nanotechnology 12, 430-433, 2017.

### May 2 — "The Quest for a Quantum Spin Liquid*"

• Presenter: Collin Broholm, Johns Hopkins University
• Host: Dmitry Reznik
• Abstract: Magnetism has commanded human wonder through millennia and it is a central component of the technologies that shape our lives. For the past 50 years scientists have been in pursuit of a radically new form of magnetism that would constitute a new state of matter: The quantum spin liquid may exist within a crystalline solid composed of atoms that carry a magnetic dipole moment. However, quantum fluctuations of these dipole moments preclude the development of conventional magnetic order even at temperature far below the scale of inter-site interactions. The result is a quantum material with unique macroscopic properties driven by quantum coherence and entanglement. If we can realize the materials physics of the quantum spin liquid these properties can be fully explored and might lead to interesting applications much as other advances we have made in our understanding of magnetism.
In the ongoing quest for a robust realization of a quantum spin liquid in the lab, a range of interesting magnetic materials and phenomena have been discovered. I shall review experiments probing interacting quantum spins on kagome, honeycomb, and triangular lattices in 2D and on the pyrochlore lattice in 3D. These frustrated quantum magnets feature an intermediate energy and temperature regime with spin-liquid-like properties but also unique low temperature phases driven by quenched disorder or lattice instabilities. Such inevitable deviations from ideal spin liquid models are interesting in their own right and their elucidation may contribute to understanding age old puzzles such as the phase diagram of V2O3 which I shall describe in greater detail in my seminar the following day.
* Supported by U.S. DoE Basic Energy Sciences, DE-FG02-08ER46544 and by the Gordon and Betty Moore foundation GBMF 4532.

For more information about colloquia this semester, contact: John Price.

Colloquia are Wednesdays at 4:00 p.m. in DUAN G1B20, unless otherwise noted.

Coffee, tea and cookies will be available before regular colloquia beginning at 3:45 p.m. in DUAN G1B31.

### August 30 — "What are Saturn’s rings made of?"

• Presenter: Sascha Kempf, University of Colorado, Boulder
• Host:
• Abstract: When Galileo Galilei discovered Saturn’s rings 450 years ago he didn’t even know that he had observed rings. It was Christiaan Huygens who proposed that Saturn is surrounded by a thin solid ring - made of metal. Earth-based spectroscopic observations in 1970 revealed that the rings in fact consist of 95% clean water ice, but the nature of the other 5% of embedded material, which gives the rings their unique reddish tint, is still unknown. It is, however, this little amount of unknown material that will bring us closer to understanding the rings’ origin and provide valuable information about the formation of the Saturnian system as a whole.

After almost 20 years in space, NASA's Cassini spacecraft has begun the final chapter of its remarkable story of exploration: its Grand Finale. Before the spacecraft plunges into Saturn’s atmosphere Cassini is undertaking a daring set of orbits that is, in many ways, a whole new mission. Starting in late April this year Cassini is performing weekly dives between the planet and the inner rim of Saturn’s rings. No other mission has ever explored this region that has been considered until a few years ago to be inaccessible for space probes. Those unique orbits allowed the Cosmic Dust Analyzer (CDA) on Cassini for the very first time to collect material originating from the main rings itself and to identify their composition.

In my talk, I will report about the exciting findings by CDA during Cassini’s swan song.

### September 6 — "Generation and detection of tunable orbital angular momentum in polarization-maintaining optical fiber"

• Presenter: Juliet Gopinath, University of Colorado, Boulder
• Host: John Price
• Abstract: In the past few years, twisted light, or light with orbital angular momentum (OAM) has captured interest a diverse array of applications. It can be used to drive micromachines and in biophotonics, OAM is used in microscopy to achieve resolution orders of magnitude better than the diffraction limit. In astronomy, the OAM of light from distant stars carries information about the inhomogeneity of the interstellar medium and the shape of black holes. In quantum information science, OAM states can be entangled, which leads to surprising demonstrations of quantum mechanics and potentially new computational possibilities. OAM-enabled communications, of all the applications, has received the majority of the attention due to the potential increase in fiber optic bandwidth that would be realized in a move from binary to a classical or quantum mechanical-vast parameter space per photon provided by the integer OAM states.

To date, specialty fiber has been used to carry OAM. In this talk, I will describe new methods for generating OAM light in commercially available polarization maintaining optical fiber. By adding up two higher order modes, generation of tunable OAM can be demonstrated. In addition, I will discuss a new quantitative detection method for light with OAM and extensions of the technique. Finally, I will present a method to control independently, both the OAM and the spatial beam profile.

Biography: Juliet Gopinath is an Associate Professor of Electrical, Computer and Energy Engineering at the University of Colorado Boulder. She received her B.S. degree in Electrical Engineering from the University of Minnesota and her M.S. and Ph.D. degrees at MIT. She worked at MIT Lincoln Laboratory from 2005 to 2009 on topics including cryogenic Yb:YAG lasers, beam combining, and mode-locked diode lasers. Since 2009, she has run a group focused on optical devices and lasers at CU Boulder. Her current research interests include ultrafast lasers, nonlinear optics, mid-infrared materials, spectroscopy, orbital angular momentum and adaptive optical devices. She is the recipient of an Air Force Young Investigator Award (2010), R & D 100 Award (2012), an NSF CAREER award (2016), the CU Provost Achievement Award (2016) and is an Associate Editor for IEEE Photonics Journal.

### September 13 — "Enabling Technology Innovation through Plasma Modeling: Sustainability and Biotechnology as the Next Frontiers"

• Presenter: Mark Kushner, University of Michigan
• Host: John Cary
• Abstract: The field of low temperature plasmas (LTPs) has provided enabling sciences and technologies that are arguably responsible for huge swaths of our industrial and high technology infrastructure.  The information technology revolution has been singularly enabled by the ability to fabricate microchips using LTPs.  Virtually every human implant is fabricated or made biocompatible using LTPs.  All non-incandescent lighting sources rely on LTPs, either directly as the source of photons or indirectly through materials fabrication.  The current generation of jet engines are enabled by LTP processing, and interplanetary missions are made possible by LTP propulsion.  Now, LTPs have the potential to treat wounds and disease, and to convert green-house gases to high value chemicals.  Many of these advances are the end result of scientifically and experimentally inspired technology development, and in some cases incremental advances over many years, with little input from modeling.  The plasma chemistry and plasma surface interactions that are responsible for these successes have untold complexity that acutely challenge diagnostics and modeling, as well as the underlying AMO (atomic, molecular, optical) physics knowledge base.  A legitimate question is – has modeling and simulation been significantly influential in the development of LTP enabled technologies?  Are modeling and simulation LTPs capable of leading innovation?  In this talk, the role and potential of modeling and simulation in the LTP innovation chain will be reviewed with examples from materials processing and the next frontiers of biotechnology and sustainability.  Examples of where modeling has provided insights that stimulated, if not enabled, technology development will be discussed.

### September 20 — "ColdQuanta Incorporated: The History and Future of a University Spinoff Company*"

• Presenter: Dana Anderson, JILA, University of Colorado, Boulder
• Host: John Price
• Abstract: ColdQuanta Inc. was founded in 2007 by three physicists and a businessman, myself, Theodor Hänsch, Jakob Reichel and Rainer Kunz.  Its mission is to develop and commercialize cold and ultracold matter technology that can enable the scientific and applications communities.  Much of ColdQuanta’s early technology emerged from a MURI grant from the Army Research Office and more so, a large DARPA grant to develop technology for guided Bose-Einstein Condensate (BEC) applications. Out of that effort came compact components for producing ultracold matter and in particular a sophisticated “atom chip” technology that made it possible to considerably reduce the size of BEC machines and similar systems.  A BEC machine that in the past took many months to build, occupied a large optical table and needed racks of electronic instrumentation can now be purchased from ColdQuanta, occupies a single rack, and can be up and running in six hours.  Since 2007 ColdQuanta has produced instruments for making cold atoms in undergraduate labs, and has enabled numerous applications and scientific experiments from optical lattices to quantum computing to the JPL/NASA mission to put cold atoms on the International Space Station.  This talk tells the story of how ColdQuanta was formed and highlights the role of students and spin-off companies in the University’s mission to provide an educated workforce, to promote scientific advancement, and to maintain this nation’s technological leadership.  It also covers some relevant “this is reality” topics such as starting a tech business, money, and conflicts of interest.  Regarding the latter:

*I hereby disclose that I have a financial interest in ColdQuanta, Inc. (!)

### September 27 — "The Quest for the New Standard Model: Searching for BSM Physics with Rare-Isotope Beams"

• Presenter: Kyle Leach, Colorado School of Mines
• Host: Eric Zimmerman
• Abstract: The development of the Standard Model (SM) has been one of the crowning achievements in modern physics, and is the cornerstone of current subatomic studies. Despite its success, the SM is known to be incomplete, and providing limits on possible physics beyond the Standard Model (BSM) is crucial to our understanding of the natural universe.  Although they are generally complex, atomic nuclei can be exploited as a laboratory for these studies through the use of rare-isotope beams (RIBs).  The production of these short-lived, very exotic isotopes has opened new avenues of research in our search for BSM physics in the era of the LHC.  This work is at the precision and sensitivity frontiers, and helps to bridge the gap between atomic, nuclear, and particle physics using novel, state-of-the-art detection techniques. In this talk, I will use these topics to highlight the significant role of the atomic nucleus in our ongoing search for additional generations of quarks, new descriptions of the weak interaction, and light dark matter. These studies play a critical role in providing the groundwork for our quest to develop the "New Standard Model".

### October 4 — "Broadening the Searchlight: New Ideas in Dark Matter Detection"

• Presenter: Kathryn Zurek, LBNL
• Host: Ethan Neil
• Abstract: Searches for massive dark matter have largely focused on a mass window near the weak scale, the so-called "WIMP window". This window is, however, becoming increasingly closed by both the LHC and the unprecedented sensitivity of direct detection experiments. At the same time, theoretical work in recent years has shown lighter dark matter candidates in a hidden sector are theoretically well-motivated, natural and arise generically in many theories beyond the standard model. New ideas are needed to search for dark matter with mass below a GeV and as light as the warm dark matter limit of a keV. We propose new ideas to search for such light dark matter with superconductors, semi-conductors, graphene, Dirac materials, and superfluid helium. We show that these same experiments, through inelastic processes, may also be sensitive to dark matter with masses in the meV to keV mass window, broadening the mass reach to light dark matter by many orders of magnitude.

### October 11 — "Spin Orbit Coupled Quantum Magnetism"

• Presenter: Kate Ross, Colorado State University
• Host: Chuck Rogers
• Abstract: Strong quantum fluctuations and spin entanglement can lead to exotic emergent many body properties of materials, such as fractionalized excitations predicted for quantum spin liquids, or the field-tuned Bose Einstein Condensation observed in quantum dimer crystals.  Traditionally, the materials space in which these types of phases are sought has been limited to materials with “pure" spin 1/2, as obtainable from Cu2+ for instance, and most theories have therefore focused on the isotropic exchange limit.  However, attention has recently shifted towards quantum materials in which an interplay of strong spin orbit coupling and crystal electric field effects lead to a "pseudo-spin" 1/2.  The magnetic interactions in these materials can be described by anisotropic effective exchange models, which can lead to new predicted quantum many body phenomena such as the Majorana fermion excitations of Kitaev quantum spin liquid, or emergent electrodynamics in quantum spin ice.  I will discuss some recent material examples that exemplify this new paradigm.

### October 18 — "The Remarkable Ways in Which Gases Dissolve and React in Water"

• Presenter: Gilbert Nathanson, Department of Chemistry, University of Wisconsin, Madison
• Host: David Nesbitt
• Abstract: Interfacial reactions between atmospheric gases and sea spray play a vital role in our air quality and climate.  These reactions also display fascinating dynamics at the atomic scale.  From this microscopic perspective, the interfacial encounter begins when gas molecules strike the surface of an aqueous solution that might contain ions and biological molecules.  We rely on understanding the physics of these gas-liquid collisions to construct a “blow-by-blow” picture of the solvation and reaction of acids, bases, and oxidizers in such complex solutions.  I will describe experiments using microjets and coated wheels that enable us to explore sea-spray mimics inside a vacuum chamber and help reveal how aerosol-mediated reactions takes place.

### October 25 — "Generation and Application of Attosecond Laser Pulses"

• Presenter: Andreas Becker, JILA, University of Colorado, Boulder
• Host: John Price
• Abstract: High harmonic generation provides a unique technique to generate coherent light up to keV photon energies, which is emitted in pulses a few tens of attoseconds in duration. Such pulses can now be used to probe dynamics in matter on the time scale of electronic motion. I will present our theoretical efforts to perform numerical calculations capturing the highly nonlinear process of attosecond pulse generation on both the microscopic level of a single atom and the macroscopic level of the generating gas medium consisting of billions of atoms. In the second part I will then discuss examples of the application of attosecond pulses to resolve electron dynamics in atoms and molecules.

### November 1 — "Transient Crosslinkers Tune the Patterns of Microtubule Filaments"

• Presenter: Jennifer Ross, University of Massachusetts, Amherst
• Host: Meredith Betterton
• Abstract: The cell is a complex autonomous machine taking in information, performing computations, and responding to the environment. To enable agile read/write capabilities, much of the molecular biochemistry that performs these computations must be transient and weak, allowing signals to be carried as a function of the concentration of numerous and coupled interactions. Traditionally, biochemical experiments can only measure strongly interacting systems that can last for long times in dilute concentrations. We have developed microscopy measurements to enable to visualization of weak, transient interactions and the resulting emergent behaviors of coupled systems. I will present excerpts from stories where many weak, transient interactions can have strong repercussions on the overall activity and can, in fact, overpower strongly interacting systems. These studies involve the microtubule cytoskeleton and the transport motor, kinesin-1.  Our results reveal a fundamentally important aspect of cellular self-organization: weak, transient interacting species can tune their interaction strength directly by tuning the local concentration to act like a rheostat. The tunability of weak, transient interactions is a fundamental activity of biological systems, and our insights will ultimately enable us to learn how to engineer these systems to create biological or biomimetic devices.

Biography: Ross is the director of the new Massachusetts Center for Autonomous Materials (MassCAM) and an award-winning biophysicist studying the organization of the microtubule cytoskeleton and microtubule-based enzymes using high-resolution single molecule imaging techniques. She has a degree in Physics and has studied the microtubule cytoskeleton for over a decade. As a Cottrell Scholar, Ross has pioneered innovative teaching techniques that are being adopted around the world. Specifically, she has taught at several international short courses on microscopy including Analytical and Quantitative Microscopy (AQLM) at the Marine Biology Laboratory and the Bangalore Microscopy Course at the National Centre for Biological Science in Bangalore, India. She has also served as the President of NESM in the past. She is also an advocate for women and under-represented groups and has a blog to help others make it in academics.

### November 8 — "Tests of quantum mechanics and gravitation with atom interferometry"

• Presenter: Mark Kasevich, Stanford University
• Host: Scott Diddams
• Abstract: Recent de Broglie wave interference experiments with atoms have achieved wavepacket separations as large as 54 cm over time intervals of 2 sec. These experiments, and their impact on gravitational and quantum physics, will be discussed.

### November 29 — "What's Next in Higgs Physics?"

• Presenter: Sridhara Dasu, University of Wisconsin
• Host: Bill Ford
• Abstract: The discovery of the Higgs boson in 2012 by the LHC experiments, ATLAS and CMS, was celebrated enthusiastically by the world. The new datasets from 2015-16 have solidified that discovery, further establishing the H(125 GeV) to be Standard Model (SM)-like. Nevertheless, explorations of the Higgs sector beyond the SM are important, as they often involve additional scalar and pseudo-scalar particles. We are making significant headway in mapping out the details of the Higgs sector already, searching for heavier Higgs bosons and rare decays of the H(125). This scalar Higgs sector could also be a portal to the "dark" sector, which we know little about from particle physics point of view. This talk will discuss the latest status of the CMS Higgs sector exploration.
Further exploration of Higgs sector is promising, but is experimentally challenging, due to low energies of the Higgs decay products.
Implications for future improvements needed for the experimental facilities will also be briefly discussed.

### December 6 — "From simple to complex atoms for atomic qubits and scalable quantum computing"

• Presenter: Mark Saffman, University of Wisconsin
• Host: Dana Anderson
• Abstract: Quantum computing is a few decades old and is currently an area where there is great excitement and rapid developments. A handful of distinct approaches have shown the capability of on-demand generation of entanglement and execution of basic quantum algorithms.
One of the daunting challenges in developing a quantum computer is the need for a very large number of qubits. Neutral atoms are one of the most promising approaches for meeting this challenge. I will give a snapshot of the current status of atomic quantum computing, describe the physics underlying neutral atom qubits and quantum gates, and show how one of the most complicated atoms in the periodic table may lead to some simple solutions to hard problems.
• Bio: Mark Saffman is an experimental physicist working in the areas of atomic physics, quantum and nonlinear optics, and quantum information processing. He has made significant contributions to the physics of optical solitons, pattern formation, sources of entangled light, and quantum computing. His current research effort is devoted to the development of neutral atom based quantum computing devices. His research team was the first to demonstrate a quantum CNOT gate between two trapped neutral atoms, and the deterministic entanglement of a pair of neutral atoms. This was done using dipole mediated interactions between highly excited Rydberg atoms. He is currently developing scalable neutral atom platforms using arrays of trapped atoms.
He is a Professor of Physics at the University of Wisconsin-Madison, and a fellow of the American Physical Society and the Optical Society of America. He has been recognized with the Alfred P. Sloan Fellowship and a University of Wisconsin Vilas Associate Award. He also serves as an Associate Editor for Physical Review A.

### December 13 — "First Results from CUORE: Majorana Neutrinos and the Search for Neutrinoless Double-Beta Decay"

• Presenter: Lindley Winslow, MIT
• Host: Alysia Marino
• Abstract: The neutrino is unique among the Standard Model particles. It is the only fundamental fermion that could be its own antiparticle, a Majorana particle. A Majorana neutrino would acquire mass in a fundamentally different way than the other particles and this would have profound consequences to particle physics and cosmology. The only feasible experiments to determine the Majorana nature of the neutrino are searches for the rare nuclear process neutrinoless double-beta decay.  CUORE uses tellurium dioxide crystals cooled to 10 mK to search for this rare process.  In this talk, I will present the first results from this detector and highlight my group’s R&D efforts and our other efforts including axions and nanoparticle-based liquid scintillators.

For more information about colloquia this semester, contact: John Price.

Colloquia are Wednesdays at 4:00 p.m. in DUAN G1B20, unless otherwise noted.

Coffee, tea and cookies will be available before regular colloquia beginning at 3:45 p.m. in DUAN G1B31.

### January 18 — "Gravitational Waves, Colliding Black Holes, And Tornadoes In Space-Time: The Dawn Of A New Astronomy"

• Presenter: David Reitze, LIGO Laboratory and University of Florida, Gainesville
• Host: Henry Kapteyn
• Abstract: The first direct detections of gravitational waves in late 2015 were made possible by a forty year experimental campaign to design, build, and operate LIGO, the Laser Interferometer Gravitational-wave Observatory. In this colloquium, I’ll cover gravitational waves and what makes them so difficult to detect and at the same time such powerful and unique probes of the universe. I’ll also give a flavor of the somewhat complicated history of how LIGO was conceived and built. Most of the presentation will focus on the interferometers, the LIGO detections and their astrophysical implications. Time permitting, I’ll give a preview of where LIGO intends to go in the next decade and beyond.

### January 25 — "15 Years of PhET Interactive Simulations: Cycles of Innovation, Learning, and Impact"

• Presenter: Kathy Perkins, University of Colorado, Boulder
• Host: John Price
• Abstract: With a collection of 134 interactive simulations for teaching science and math, and over 100 million simulation uses per year worldwide, the PhET Interactive Simulations project has come a long way since its beginning in 2002. Founded by our colleague Carl Wieman as the “Physics Education Technology” project, his vision was to make physics engaging and accessible for all learners by tapping into a natural curiosity about real world phenomena. The journey from 2002 to today has included many cycles of innovation and learning as PhET expanded from physics to chemistry to math, from college to middle school, and from a local resource to an international mainstay. We will reflect on these past cycles – the challenges and the solutions – and how physics and the physicist’s perspective has shaped and advanced our work throughout. We will also look ahead to what’s on the horizon for PhET – bringing science inquiry to students with disabilities, advancing assessment of science practices, transforming middle school math, and building a sustainable business model.

### **Special Colloquium** Monday, January 30 — "Unlocking neutrino mysteries with the NOvA experiment"

• Presenter: Christopher Backhouse, California Institute of Technology
• Host: Kevin Stenson
• **NOTE SPECIAL LOCATION: DUAN G130
• Abstract: The 2015 Nobel Prize in Physics was awarded for the discovery of the phenomenon of neutrino oscillations, which implies that neutrinos are not massless as we had previously believed. This raises a wealth of new and intriguing questions. What is the ordering of the neutrino mass states? Might they violate matter/antimatter symmetry? What structure, if any, does the neutrino mixing matrix have? The NOvA experiment directly addresses these questions by measuring changes undergone by a powerful neutrino beam over an 810 km baseline, from its source at Fermilab, Illinois to a huge 14 kton detector in Ash River, Minnesota. I will give a brief overview of neutrino oscillations, then present our latest results, their implications, and prospects for the future.

### February 1 — "The 1,358,954,496 Matrix Elements to Get From SUSY Diff Eq's to Pictures, Codes, Card Games, Music, Computers, and Back Again"

• Presenter: S. James Gates, University of Maryland
• Host: Clifford Bridges
• Abstract: In this presentation a discussion is given of a recent derivation of a supersymmetrical QM representation spectrum that took some surprising twists and turns along the way.

### February 8 — "Quarks of Many Colors"

• Presenter: Tom DeGrand, University of Colorado Boulder
• Host: John Price
• Abstract: Numerical simulation of quantum chromodynamics  (QCD) is a successful way to compute the properties of strongly interacting particles from first principles. However, it doesn't give much insight into why the numbers are what they are. Long ago Hooft argued that QCD could be understood most simply when the “three'” of the three colors was taken to be a large number. But nobody could compute anything like a reduced matrix element with this idea. Recently, people have begun to marry these two stories.  I'll tell you a bit about them both, put them together, and  see what we find. Remarkable regularities emerge.

### Special Colloquium — Monday, February 13 "Physics at the LHC: Why and How to go Beyond the Higgs Discovery"

• Presenter: John Alison, University of Chicago
• NOTE SPECIAL LOCATION: DUAN G130
• Host: Kevin Stenson
• Abstract: The Standard Model (SM) of particle physics is a spectacularly successful theory that is known to be fundamentally incomplete.  The recent discovery of the Higgs boson at the Large Hadron Collider is, on one hand, the final missing piece of the SM and, on the other, a window into what lies beyond.  I will discuss the motivations and experimental challenges of searching for physics beyond the SM at the LHC.  Emphasis will be placed on using the Higgs boson as a probe of new physics in processes involving pairs of Higgs bosons.

### February 15 — "Looking for Fossils of the Big Bang in Molecular Spectra"

• Presenter: Eric Cornell, JILA and University of Colorado, Boulder
• Host: John Price
• Abstract: How can you learn about the early moments of the universe? How can you discover evidence for new sub-atomic particles? We usually think of ever-more exotic telescopes, or of ever-larger particle accelerators. I will talk about the third leg of the stool: precision measurement. We will see that the humble two-atom molecule should be thought of as an ultrahigh electric-field laboratory.

### Special Colloquium — Monday, February 20 "Strategies for searches of physics beyond the Standard Model in the XXI century"

• Presenter: Manuel Franco Sevilla, University of California, Santa Barbara
• NOTE SPECIAL LOCATION: DUAN G130
• Host: Kevin Stenson
• Abstract: At the end of the XIX century, Lord Kelvin summarized a widespread feeling among physicists by saying that "physics is essentially complete, save for two little clouds". The "clouds" he was (apocryphally) referring to were the puzzling results from two measurements, the Michelson-Morley experiment and the Black-body spectrum, whose explanations ushered in an unprecedented era of discoveries that stretched throughout most of the XX century. After the culmination of the Standard Model in the 70's, the field of particle physics has found itself in a similar situation. Today, the "clouds" guiding the searches for physics beyond the Standard Model are issues like dark matter or the hierarchy problem. Using SUSY searches at CMS and the measurement of B->D(*)TauNu decays at BaBar as models, I will give an overview of some of the main strategies that are being followed in the quest to find new physics in the XXI century.

### February 22 — "The Difficult Search for CP Violation in Neutrinos"

• Presenter: Michael Wilking, Stony Brook University
• Host: Kevin Stenson
• Abstract: To observe CP violation, experiments must make precise, differential measurements of the appearance of electron neutrinos and anti-electron neutrinos. This requires unprecedented control of systematic uncertainties, and, in particular, an understanding of neutrino-nucleus interactions that is beyond the capabilities of existing theoretical models. The resulting "neutrino energy measurement problem" that will be confronted by current and future long-baseline neutrino oscillation experiments, as well as potential experimental solutions, will be discussed.

### March 1 — "Searching for Supersymmetry at the LHC"

• Presenter: Keith Ulmer, Texas A&M
• Host: Kevin Stenson
• Abstract: The Large Hadron Collider (LHC) at CERN currently provides the highest energy particle collisions ever produced in a laboratory. These collisions were reconstructed and analyzed by the CMS and ATLAS experiments to claim the discovery of the Higgs Boson in 2012, thus completing the standard model of particle physics. This talk explores what's next for the LHC, including the implications of the Higgs discovery on the search for new physics beyond the standard model. In particular, such open questions as the nature of dark matter and the gauge hierarchy problem may find eloquent solutions in supersymmetry, a proposed new symmetry of nature relating fermions and bosons. I will discuss the current state of experimental searches for supersymmetry at CMS, including the near term prospects for discovery, and will conclude with an example of the innovative new technological solutions being explored to continue the hunt for new physics into the High Luminosity LHC era set to begin in the coming decade.

### March 8 — "Searching for axion and hidden photon dark matter with lumped element electromagnetic resonators and SQUIDs"

• Presenter: Kent Irwin, Stanford University
• Host: Nils Halverson
• Abstract: About 85% of the matter in the universe is made up of an unknown "dark" component that is mostly non-baryonic. For several decades, searches for this mysterious substance has principally focused on one candidate particle: the WIMP. Superconducting Quantum Interference Devices (SQUIDs) have played an important role in these searches, which have successfully ruled out significant phase space for WIMP dark matter. Recently, there has been a surge in theoretical interest in ultra-light-field dark matter, including QCD axions (spin 0 bosons) and hidden photons (spin 1 bosons). The Dark Matter Radio (DM Radio) is a tunable superconducting high-Q lumped-element resonator also using SQUIDs for detection. I will discuss the motivation, status and prospects for the DM Radio experiment in searching for both axions and hidden photons, and the remarkable phase space that DM Radio will search over the next several years.

### March 15 — "Tunable Materials and Metasurfaces – from Quantum to Perfect"

• Presenter: Harry Atwater, California Institute of Technology
• Host: Scott Diddams
• Abstract: Tuning the Fermi level and complex dielectric function of low-dimensional nanophotonic structures including layered materials and nanoantenna arrays enables scientific exploration of quantum materials such graphene, phosphorene and topological insulators and, as well applications including electronic phase and amplitude modulators for the near infrared (conducting oxides) and mid infrared (graphene). We discuss light-matter interactions in materials and report dynamically tunable metasurfaces exhibiting >π phase modulation and ‘perfect’ absorption approaching 100%.

### March 22 — "High-Capacity Optical Communications using Multiplexing of Multiple Orbital-Angular-Momentum Beams"

• Presenter: Alan Willner, University of Southern California
• Host: Scott Diddams
• Abstract: Optical communications has historically experienced tremendous capacity growth by multiplexing many channels and transmitting them simultaneously. Recently, the community has turned to research the possibility of space-division-multiplexing (SDM) as the next domain to exploit, and multiple spatially overlapping orthogonal modes can achieve a subset called mode-division-multiplexing (MDM). Indeed, the ability to multiplex multiple data-carrying modes over the same physical medium represents the potential for increasing system capacity and spectral efficiency.
Generating different amounts of orbital-angular-momentum (OAM) on different optical beams has emerged as a technique for such mode multiplexing. A beam can carry OAM if its phase front twists in a helical fashion as it propagates, and the amount of OAM corresponds to the number of 2*pi phase shifts that occur in the azimuthal direction. Each OAM beam is orthogonal to other beams, and such beams can be efficiently multiplexed, transmitted, and demultiplexed with little inherent crosstalk. This presentation will explore the achievements of and challenges to OAM-based optical and millimeter-wave communication systems, including transmission, turbulence compensation, and link design.

### April 5 — "Thermoelectrics and Thermoelectric Materials"

• Presenter: David Singh, University of Missouri
• Host: Gang Cao
• Abstract: Thermoelectric devices are used for the conversion of thermal and electrical energy. They offer a number of advantages over competing technologies including scalability to small sizes and temperature differences, simple reliable designs and often low cost. However, these devices have not seen wide application in energy applications due to their limited conversion efficiency. This is a consequence of the limited performance of current thermoelectric materials, which can be characterized by a dimensionless figure of merit, ZT=σS2T/κ. There is no known fundamental limit on ZT. However, the combination of transport parameters entering ZT is a combination that does not occur in ordinary materials. This talk presents an overview of ZT and discusses strategies for optimizing ZT as well as recent results that point to ways of identifying new high ZT compositions. An important finding is that electronic structure plays a remarkably subtle role in thermoelectric performance that can however be simply visualized in terms of iso-energy surfaces. Finally, a connection is drawn between topological insulators and high ZT thermoelectrics, explaining the overlap between these two interesting materials classes. Characteristics that can be used to identify new thermoelectric compositions are presented and discussed.

### April 12 — "Structure and Dynamics with Ultrafast Electron Microscopes… or how to make atomic-level movies of molecules and materials"

• Presenter: Brad Siwick, McGill University
• Host: John Price
• Abstract: In this talk I will describe how combining ultrafast lasers and electron microscopes in novel ways makes it possible to directly ‘watch’ the time-evolving structure of condensed matter on the fastest timescales open to atomic motion.  By combining such measurements with complementary (and more conventional) spectroscopic probes one can develop structure-property relationships for materials under even very far from equilibrium conditions.

I will give several examples of the remarkable new kinds of information that can be gleaned from such studies and describe how these opportunities emerge from the unique capabilities of the current generation of ultrafast electron microscopy instruments.  For example, in diffraction mode it is possible to identify and separate lattice structural changes from valence charge density redistribution in materials on the ultrafast timescale and to identify novel photoinduced phases that have no equilibrium analogs.   It is also possible to directly probe the strength of the coupling between electrons and phonons in materials across the entire Brillouin zone and to probe nonequilibrium phonon dynamics (or relaxation) in exquisite detail.  In imaging mode, real space pictures of nano- to microstructural evolution in materials at unprecedented spatio-temporal resolution can be obtained.

I will assume no familiarity with ultrafast lasers or electron microscopes.

References

1. G. Sciani and  R. J. D. Miller, Femtosecond electron diffraction:  Heralding the era of atomically resolved dynamics, Rep. Prog. Phys. 71 (2011) 096101
2. R. P. Chatelain, V. Morrison, C. Godbout, and B.  J. Siwick, Ultrafast electron diffraction with radio-frequency compressed electron pulses, Appl. Phys. Lett. 101 (2012) 081901.
3. V. Morrison, R. P. Chatelain, K. Tiwari, A. Hendaoui, M. Chakker and B.  J.  Siwick, A photoinduced metal-like phase of monoclinic vanadium dioxide revealed by ultrafast electron diffraction, Science 346 (2014) 445 – 448.
4. R. P. Chatelain, V. Morrison, Bart L. M. Klarenaar and B.  J.  Siwick, Coherent and incoherent electron-phonon coupling in graphite observed with radio-frequency compressed ultrafast electron diffraction, Phys. Rev. Lett. 113 (2014) 235502.
5. L. Nikolova, M. Stern, T. LaGrange, B. Reed, N. Browning, G. H. Campbell, J.-C. Kieffer, F. Rosei and B. J. Siwick, Complex crystallization dynamics in amorphous germanium studied with dynamic TEM. Phys. Rev. B 87 (2013) 064105.

### April 26 — "Building a Proportional Cell: Lessons from Physics"

• Presenter: Jané Kondev, Brandeis University
• Host: Loren Hough
• Abstract: The inside of a living cell is spatially organized into different functional structures called organelles. For example, the nucleus is a membrane bound compartment that contains the cell's DNA, while the cytoskeleton is made up of dynamic protein fibers which allow cells to move and change shape.

Gulliver noticed 140 years ago that the size of the cell's nucleus is proportional to the size of the cell. Similar observations have been made about other micron-sale structures within the cell. These experiments suggest that cells measure and control the size of their organelles, and they raise a simple question: How does the cell establish a micron-scale ruler with nothing more at its disposal than nanometer-sized molecules that diffuse around the cell and on occasion bump into each other?  In this talk I will describe quantitative experiments and related theory that are beginning to reveal general principles of how cells control the size of their organelles.

### May 3 — "Imaging the Surface States of a Strongly Correlated Topological Insulator"

• Presenter: Jennifer Hoffman, Harvard University
• Host: Dan Dessau and Minhyea Lee
• Abstract: The prediction and subsequent discovery of robust spin-polarized surface states on topological band insulators has launched a new subfield of physics over the last decade. In the last few years it has been recognized that when topology is combined with strong electron-electron correlations, even more interesting and potentially useful states of matter can arise, such as new topological classifications, fractionalized states, and many-body localization that preserves the topology of the insulating state against thermal destruction. Here we show the first direct proof of a strongly correlated topological insulator. Using scanning tunneling microscopy to probe real and momentum space structure, our measurements on the heavy fermion material SmB6 reveal the evolution of the insulating gap arising from strong interactions. Within the narrow gap, we directly image a dispersing surface state that converges to a Dirac point close to the chemical potential. Our observations present the first opportunity to explore a strongly correlated topological state of matter.

For more information about colloquia this semester, contact: John Price.

Colloquia are Wednesdays at 4:00 p.m. in DUAN G1B20, unless otherwise noted.

Coffee, tea and cookies will be available before regular colloquia beginning at 3:45 p.m. in DUAN G1B31.

### August 24 — "NASA’s Juno Mission to Jupiter: What’s Inside the Giant Planet?"

• Presenter: Fran Bagenal, University of Colorado Boulder
• Host: Mihaly Horanyi
• Abstract: Jupiter is a planet of superlatives: the most massive planet in the solar system, rotates the fastest, has the strongest magnetic field, and has the most extensive satellite system of any planet. NASA’s Juno mission was launched in August 2011 and went into orbit over Jupiter’s poles on July 4th this summer.  Juno’s principal goal is to understand the origin and evolution of Jupiter. Underneath its dense cloud cover, Jupiter safeguards secrets to the fundamental processes and conditions that governed our solar system during its formation. As our primary example of a giant planet, Jupiter can also provide critical knowledge for understanding the planetary systems being discovered around other stars. With its suite of science instruments, Juno will investigate the existence of a solid planetary core, map Jupiter's intense magnetic field, measure the amount of water and ammonia in the deep atmosphere, and observe the planet's auroras. Juno will let us take a giant step forward in our understanding of how giant planets form and the role these titans played in putting together the rest of the solar system. In Greek and Roman mythology, Jupiter drew a veil of clouds around himself to hide his mischief. It was Jupiter’s wife, the goddess Juno, who was able to peer through the clouds and reveal Jupiter’s true nature.  Juno is also the first spacecraft to fly over Jupiter’s aurora and will measure both the energetic particles raining down on the planet and the bright “northern & southern lights” they excite.

### August 31 — "Cosmic Dust Research at the Colorado Dust Accelerator"

• Presenter: Tobin Munsat, University of Colorado Boulder
• Host: John Price
• Abstract: Cosmic dust grains play a central role in astrophysics and planetary science; the interaction of dust grains with planetary surfaces and atmospheres can drive weathering processes, surface chemistry (for airless bodies), and even atmospheric chemistry on Earth. Dust-detecting instruments can provide insight into the environment where the particles were formed, whether that is the interstellar medium, comets, asteroids, or even ejected from the surfaces of planets and moons. From a basic physics point of view, hypervelocity impact experiments can access extremely high energy density levels. To address many facets of cosmic dust research in the lab, we have recently developed a dust accelerator on the east campus of CU. This is a 3 MV electrostatic linear accelerator which launches particles in the size range of 0.1 to a few micrometers and velocities up to 100 km/s onto a variety of targets. This talk will describe the basic details of the accelerator and provide an overview of several lines of research being carried out by our group.  Specifically, I will discuss hypervelocity impact cratering experiments in thin films, impact experiments into cryogenic (ice) targets, making "shooting stars" in the lab, and the local development of dust detector instruments that have flown to the moon and will soon fly to Jupiter's moon Europa.

### September 7 — "The End of Inflation"

• Presenter: Tom Giblin, Kenyon College
• Host: Ethan Neil
• Abstract: The evidence for a hot, dense, early stage of the Universe is overwhelming.  Setting up a Universe in this hot-dense stage is more of a challenge.  While Cosmic Inflation as a paradigm has been successful at negotiating  the issues of the Hot Big Bang, its conclusion is marked by a cold, empty state that needs to quickly and efficiently reheat.  Violent processes, turbulent phase transitions and non-linear processes characterize this period and might help us shed light on the particle physics of the very young, very energetic early Universe.  I will describe how we have been using large numerical simulations to calculate precision observables that will help to constrain the growing number of early universe scenarios.

### September 14 — "Apples vs. Oranges: Comparison of Student Performance in a MOOC vs. a Brick-and-Mortar Course"

• Presenter: Michael Dubson, University of Colorado Boulder
• Host: John Price
• Abstract: In the fall of 2013, my colleagues and I taught the calculus-based introductory physics course to 800 tuition-paying students at the University of Colorado at Boulder. At the same time we taught a free massive open online course (MOOC ) version of the same course, through Coursera.com. The initial enrollment in the MOOC was 10,000 students, of whom 255 completed the course. Students in both courses received identical lectures with identical embedded clicker questions, identical homework assignments, and identical timed exams. We present data on participation rates and exam performance for the two groups. We find that the MOOC is like a drug targeted at a very specific population. When it works, it works well, but it works for very few students. This MOOC worked well for older, well-educated students, who already had a good understanding of Newtonian mechanics.

### September 21 — "Tragic tale of the mathematical genius Ramanujan"

• Presenter: Ramamurti Shankar, Yale University
• Host: Rahul Nandkishore
• Abstract: In this talk I will describe the remarkable life and mathematics of Srinivasa Ramanujan (1887-1920), an unknown self-educated clerk from South India who stunned the world of western mathematics with his results on number theory, modular functions etc., that continue to challenge us till this day. I will describe his early life in India, his discovery by Cambridge mathematician G H Hardy, his few years in Cambridge and his untimely death at age 32.

### September 28 — "Shared vibrations:  How photosynthetic light harvesting approaches 100% efficiency”

• Presenter: David Jonas, Department of Chemistry and Biochemistry, University of Colorado Boulder
• Host: John Price
• Abstract: Almost all life on earth depends on photosynthesis, and almost all the power our civilization uses has been stored as fuel by photosynthesis.  In photosynthesis, light is harvested by antenna proteins that can transfer the photon’s energy to a reaction center with near unit quantum efficiency.  The remarkable efficiency of these energy transfer processes has been a mystery for over 60 years and we cannot replicate it artificially.  Recent femtosecond two-dimensional (2D) spectroscopy experiments on antenna proteins found signatures initially attributed to electronic coherence that have sparked discussion about the role of quantum mechanics in biology; it is puzzling that these signatures persist for longer than the apparent energy transfer timescale.   We have recently shown that intramolecular vibrations shared across pigments can drive electronic energy transfer outside the Born-Oppenheimer picture of fast electrons and slow vibrations.  Such shared vibrations on the ground electronic state of the antenna generate all of the observed 2D signatures and their properties reveal the design principle for the antenna.  There are indications that this new mechanism may be operative in a variety of antenna proteins using 5 different photosynthetic pigments that are responsible for over half of the light harvesting on our planet.

### **Special Colloquium/Nuclear Particle Physics Seminar** Monday, October 3 — "The Physics of Non-Hydrodynamic Modes"

• Presenter: Paul Romatschke, University of Colorado Boulder
• NOTE SPECIAL LOCATION: DUAN G125
• Abstract: Examples for hydrodynamic collective modes are sound waves, shear and diffusive modes. But what are non-hydrodynamic collective modes? Most physicists likely have never ever heard about non-hydrodynamic modes in their entire career. Indeed, there does not seem to be a single textbook on this topic. This colloquium will give an introduction to the physics of non-hydrodynamic modes, featuring gravitational waves, string theory predictions for experiment, the coolest and hottest stuff on earth and high-temperature superconductors.

### October 5 — “A synthetic quantum magnet made of hundreds of trapped ions”

• Presenter: John Bollinger, NIST Boulder
• Host: Scott Diddams
• Abstract: Entanglement between individual quantum objects exponentially increases the complexity of quantum many-body systems, so systems with more than 30-40 quantum bits cannot be fully studied using conventional techniques and computers. To make progress at this frontier of physics, Feynman’s pioneering ideas of quantum computation and quantum simulation are now being pursued in a wide variety of well-controlled quantum platforms.  Trapped-ions are naturally suited for simulating quantum magnetism, and exhibit desirable properties such as high-fidelity state preparation and readout, and long trapping and coherence times.  I will discuss how variable range, quantum magnetic interactions can be engineered with trapped ions, focusing on our work with 2-dimensional arrays of several hundred ions crystallized in a Penning ion trap.  In particular, I will highlight our recent experiments that benchmark quantum dynamics and entanglement, and utilize our ability to time-reverse the dynamics to measure out-of-time-order correlation functions that quantify the spread of quantum information throughout the system.

### October 12 — "On string theory, particle physics and cosmology"

• Presenter: Fernando Quevedo, Director - ICTP, Trieste and Cambridge University
• Host: Shanta de Alwis
• Abstract: An overview will be given for the recent developments in string theoretical scenarios to address particle physics and cosmology questions.

### October 19 — "From BEC to CEO: the Entrepreneurial Experience"

• Presenter: Chris Myatt, CEO - MBio Diagnostics
• Host: Scott Diddams
• Abstract: Can academic training in physics – at CU, JILA, and at NIST – prepare you to start a company?  While the subject of your research may not be directly applicable to industrial problems—in my case, Bose-Einstein condensation and quantum computing—the skill sets and tools you develop are of great value in preparing you to start a company, or to find a job in industry.  I will discuss briefly the two companies I have founded, provide an overview of the technology of each, what it takes to get going, and the lessons learned in doing so.

### October 26 — "Exploiting Disorder for Global and Local Response"

• Presenter: Sidney Nagel, University of Chicago
• Host: Noel Clark
• Abstract: We are customarily taught to understand ordinary solids by considering perturbations about a periodic structure.  This approach becomes increasingly untenable as the amount of disorder in the solid increases.  In a crystal with only one atom per unit cell, all atoms play the same role in producing the solid's global response to external perturbations. Disordered materials are not similarly constrained and a new principle emerges: independence of bond-level response. This allows one to drive the system to different regimes of behavior by successively removing individual bonds. We can thus exploit disorder to achieve unique, varied, textured and tunable global response. We can use similar pruning techniques to achieve long-range interactions inspired by allosteric behavior in proteins. This allows a local input strain to control the local strain at a distant site in the network.

### November 2 — "A Bridge Too Far: The Demise of the Superconducting Super Collider"

• Presenter: Michael Riordan, Author
• Host: Allan Franklin

### January 25 — "Magnetic Resonance Physics Through a Cognitive Neuroscientist's Eyes"

• Presenter: Marie Banich, Director of the Institute of Cognitive Science
• Host: Jerry Peterson
• Abstract: Magnetic resonance imaging has transformed the ability of neuroscientists to make linkages between behavior, brain structure, and brain function. In this talk, I will provide a very broad overview of what types of information these techniques can apply (and a rudimentary discussion of how they work) and why they have been so transformative for our field. In addition, I will speak to some limitations of these methods. Finally, a description on the new human magnetic resonance imaging system on the Boulder campus will be provided with an eye for how it might be a resource for the Physics community on campus.

### February 1 — "From Viscous Fluids to Fermi Surfaces: The Lore of Anti-De Sitter Black Holes"

• Presenter: Steve Gubser, Princeton
• Host: Oliver DeWolfe
• Abstract: Through the magic of string dualities, black holes in negatively curved spacetimes capture phenomena as diverse as viscous fluid dynamics and Fermi surfaces. I will give an overview of what these black holes look like and how they are used in applications to heavy ion collisions and aspects of condensed matter theory. Time permitting, I will discuss not only viscous fluid dynamics and Fermi surfaces, but also heavy quark energy loss and holographic superconductors.

### February 8 — "Particle Physics Today"

• Presenter: Lisa Randall, Harvard
• Host: Oliver DeWolfe
• Abstract: New developments in physics have the potential to radically revise our understanding of the world: its makeup, its evolution, and the fundamental forces that drive its operation. The Large Hadron Collider, which houses a 27 km ring accelerating protons to enormously high energies 100 meters underground, contains the most extensive and elaborate experiments ever built. In this lecture I will explore what theories predict and the nature of the experiments that study these tiny distances.

### February 15 — "Magnetic Dynamos in the Lab: Progressing from Liquid Metal to Plasmas

• Presenter: Cary Forest, University of Wisconsin
• Host: Tobin Munsat
• Abstract: Every astrophysical plasma is, as far as we can measure, magnetized and turbulent. How these magnetic fields spontaneously self-generate, through a process called the dynamo, and then act back on their surroundings is a central question in plasma astrophysics. Dynamos occur in plasmas that range from small and dense stellar plasmas to diffuse plasmas in galaxy clusters, and can have impacts that range from making life possible on Earth to controlling accretion onto black holes.
Laboratory experiments on dynamos have been pursued for the last decade using large volumes of fast flowing, electrically neutral liquid metals to create conditions in which magnetic induction dominates resistive dissipation of electrical currents. In some cases, this creates a self-excited magnetic dynamo. This talk begins with an overview of the basics of dynamos, also demonstrating how lab experiments relate to natural dynamos in the Earth (liquid metal), and the Sun (plasma). As one example of this, our group has recently measured the turbulent electromotive force (through correlated fluctuations of velocity and magnetic field) in a 200 horsepower, 1 meter diameter liquid sodium experiment. We have directly observed how turbulence, on average, enhances the effective resistivity of the liquid metal and more rapidly transports magnetic flux. Recent experiments on a novel plasma device will then be described that establish the feasibility for creating a large, steady-state, fast flowing, weakly magnetized, hot plasma, exhibiting all of the critical parameters for dynamo studies. Remarkably, by changing plasma composition and density, the fluid Reynolds number can be independently controlled. Finally, we describe a much larger device, now under construction, which is projected to extend accessible parameter space to a regime much closer to astrophysical dynamos than liquid metals.

### February 22 — "Quantum Networks of Trapped Atomic Ions"

• Presenter: Chris Monroe, Physics, JQI and University of Maryland
• Host: Jun Ye
• Abstract: Trapped atomic ions are standards for quantum information processing, with each atom storing a quantum bit (qubit) of information in appropriate internal electronic levels. All of the fundamental quantum operations have been demonstrated between small numbers of atoms, and the central challenge now is how to scale the system to larger numbers of interacting qubits. The Coulomb interaction between trapped ions allows entangling operations through the collective motion of the ion crystal, which can be excited through the state-dependent optical dipole forces. When such an force is applied globally, an effective spin-spin interaction emerges whose sign and range can be precisely controlled with the laser, and any possible spin correlation function can be measured with standard state-dependent fluorescence techniques. This allows the quantum simulation of interesting spin models that possess nontrivial ground states for the investigation of quantum phase transitions, quantum frustration, and the emergence of spin liquid behavior. Such a quantum network may be limited in size by the stability and coherence of the motion of larger ion crystals, and current efforts are devoted to multiplexing to even bigger systems by shuttling ions through complex ion trap structures or mapping qubits onto photons that can allow the probabilistic entanglement between remotely-located atoms. Work on all of these fronts will be reported, including quantum simulations of magnetism with N=16 atomic qubits as well as progress on operating deterministic gates between atoms separated by macroscopic distances.

### February 29 — "How Symmetric is the Electron? Looking for Out-of-roundness of 10-15 Femtometers"

• Presenter: Eric Cornell, JILA, University of Colorado Boulder
• Host: Leo Radzihovsky
• Abstract: The electron's electric dipole moment (eEDM) will be sensitive to particle physics beyond the standard model. We make use of the extreme electric fields found within a molecular bond to pursue an experiment to set a new limit on eEDM at a level that should severely constrain supersymmetric models.

### March 7 — The Geodynamo from a Whole Earth Perspective

• Presenter: Peter Olson, Johns Hopkins University
• Host: Shijie Zhong
• Abstract: The geomagnetic field is generated through self-sustaining dynamo action in the Earth's core. The first part of this talk surveys the main components of the geodynamo, focusing on the roles of convection in the fluid outer core, solidification of the inner core, and heat transfer to the mantle in the dynamo process. The second part of this talk examines a defining property of the geodynamo, the phenomenon of magnetic polarity reversals, which represents the most extreme form of geomagnetic variability. Progress in resolving the history of geomagnetic reversals and the structure of the geomagnetic field during polarity transitions has been matched by recent advances in modeling the reversal process in the core using first-principles numerical dynamos. Numerical dynamos reveal that geomagnetic reversals are sensitive to convection in the core, Earth's rotation, and the interactions between the core and the mantle. Although individual geomagnetic reversals appear to be stochastic, their long-term sequencing includes time periods with frequent reversals alternating with long-lasting stable magnetic polarity superchrons over approximately 200 million year cycles. A proposed explanation for these ultra-low frequency cycles is the modulation of heat transport from the core to the mantle on geologic time scales.

### March 14 — "Transport Experiments on Surface States of Topological Insulators"

• Presenter: N.P. Ong, Princeton
• Host: Minhyea Lee
• Abstract: The topological surface states in 3D materials predicted by Kane, Mele and Fu were rapidly detected by surface sensitive spectroscopy (ARPES and STM). Transport experiments to investigate their properties have been more challenging. Following a brief introduction, I will survey experiments in which the surface states were first detected by magnetoresistance oscillations in Bi2Se3 and Bi2Te3. More recently, the hybrid Bi2Te2Se has emerged as the most attractive candidate for transport experiments. I will describe a recent experiment showing that the occupation of the surface Dirac cone can be tuned by liquid gating.

### March 21 — "Once Upon a Time in Kamchatka: The Extraordinary Search for Natural Quasicrystals"

• Presenter: Paul Steinhardt, Princeton
• Host: Leo Radzihovsky
• Abstract: A quasicrystal is an exotic state of matter with an atomic structure analogous to a Penrose tiling, exhibiting symmetries forbidden to crystals, such as five-fold symmetry in the plane and icosahedral symmetry in three dimensions. The concept of quasicrystals was first introduced twenty-eight years ago and over a hundred types have been synthesized in the laboratory by now. But could Nature have beaten us to the punch? The campaign to answer that question makes for one of the stranger scientific stories you are ever likely to hear.

### April 4 — "Wiring up Quantum Systems: Fun with Artificial Atoms and Microwave Photons "

• Presenter: Steve Girvin, Yale
• Host: Leo Radzihovsky
• Abstract: A revolution is underway in the construction of ‘artificial atoms’ out of superconducting electrical circuits. These macroscopic ‘atoms’ have quantized energy levels and can emit and absorb quanta of light (in this case microwave photons), just like ordinary atoms. Unlike ordinary atoms, the properties of these artificial atoms can be engineered to suit various particular applications, and they can be connected together by wires to form quantum ‘computer chips.’ This so-called ‘circuit QED’ architecture has given us the ability to test quantum mechanics in a new regime using electrical circuits and to construct rudimentary quantum computers which can perform certain tasks that are impossible on ordinary classical computers. [1] ‘Wiring up quantum systems,’ R.J. Schoelkopf and S.M. Girvin, Nature 451, 664 (2008).

### April 11 — "A Little Big Bang: Strong Interactions in Ultracold Fermi Gases"

• Presenter: Martin Zwierlein, Physics, MIT
• Host: Leo Radzihovsky
• Abstract: Fermions, particles with half-integer spin such as electrons, protons and neutrons, are the building blocks of matter. When fermions strongly interact, complex phenomena emerge, for example high-temperature superconductivity or superfluidity in neutron stars. Ultracold Fermi gases of atoms are a new type of strongly interacting fermionic matter that can be created and studied in the laboratory with exquisite control. For example, we can study the collision of "spin up" and "spin down" Fermi gases with the strongest interactions allowed by quantum mechanics. In equilibrium, direct absorption images of the trapped atomic gas reveal the entire thermodynamics of the system, including the transition into the superfluid state. Scaled to the density of electrons, superfluidity would occur far above room temperature. We were recently able to follow the evolution of fermion pairing from three to two dimensions, connecting quite directly to models of layered superconductors. Our measurements in and out of equilibrium provide benchmarks for current many-body theories and will help to understand other strongly interacting Fermi systems, such as high-temperature superconductors and neutron stars.

### April 18 — "Topological Order and Long Range Quantum Entanglements -- From Origins to New Quantum States of Matter"

• Presenter: Xiao-Gang Wen, Physics, MIT
• Host: Leo Radzihovsky
• Abstract: What is the origin of fractional charges and fractional statistics in FQH states? What is the origin of light? It turns out that long range entanglement is the reason why fractional charges and fractional statistics can appear FQH state. Long range entanglement is also the reason why waves that satisfy Maxwell equation can appear in some qubit (spin) systems. Long range entanglement also lead to a deeper understanding of gapped quantum phases. It allows us to obtain a classification of interacting topological insulators/superconductors, as well as the much more general symmetry protected topological phases, and intrinsic topological phases.

### April 25 — "Redefining Snake Oil: Lessons Learned from Pythons that Could Benefit People"

• Presenter: Leslie Leinwand, MCDB, University of Colorado Boulder
• Host: Meredith Betterton
• Abstract: The major research interests of Dr. Leinwand’s laboratory are the biology of inherited diseases of the heart and how gender and diet modify the heart. Recently, her work has focused on the extreme biology of the Burmese python and how this biology might be translated to therapeutics for human heart disease. In the wild pythons do not eat very often but when they do eat, they eat enormous meals that can equal their body mass. To digest such a meal, almost all organs in the body grow very rapidly and then regress in size just as rapidly. Her laboratory’s investigations into the mechanisms responsible for the increase in heart mass in Burmese pythons after a large meal have revealed information that may be applicable to the mammalian heart. They found that heart growth in pythons is characterized by cellular enlargement in the absence of cell proliferation and by activation of beneficial signaling pathways much like the process by which highly conditioned athletes increase the sizes of their hearts. Despite extremely high levels of circulating lipids, which would be toxic to the heart, the post-fed python heart does not accumulate fats. Instead, there is robust activation of pathways of fatty acid transport and oxidation combined with increased expression and activity of a cardioprotective enzyme. They also identified a specific combination of three fatty acids in python plasma that promotes beneficial heart growth when injected into either pythons or mice. The long term goal is to promote heart health using the biology of the python.

### May 2 — "The Physical Basis for Biological Morphogenesis"

• Presenter: L Mahadevan, Harvard University
• Host: Leo Radzihovsky
• Abstract: The range of shapes in the plant (and animal) world is "enough to drive even the sanest man mad", wrote Darwin. Motivated by qualitative and quantitative biological observations, I will show that there is a "method in the madness" - using examples of growth and form in cells, tissues and organs such as a freely growing pollen tube, undulating fringes on a leaf or petal, the growth of floral spurs, the looping of the gut and the coiling of tendrils. In each case, we will see how a combination of biological and physical experiments, mathematical models and computations allow us to unravel the quantitative basis for the diversity and complexity of biological form, with tantalizing links to evolutionary canalization, biomimetic technologies, and new aspects of geometry and analysis.

Fall 2011 Colloquium Schedule

Colloquia are Wednesdays at 4:00 p.m. in DUAN G1B20, unless otherwise noted.

Coffee, tea and cookies will be available before regular colloquia beginning at 3:45 p.m. in DUAN G1B31.

## August 24 — "First Galaxies, First Stars, and the Reionization Epochs of H and He"

• Presenter: Michael Shull, Astrophysical and Planetary Science, University of Colorado at Boulder
• Host: Paul Beale
• Abstract: The universe is thought to have originated in a hot fireball (Big Bang) whose expansion in the presence of dark matter and baryons led to cooling, formation of large-scale structure, the "Dark Ages", and eventually to the first stars and galaxies. I will describe theoretical studies of the expectations for the earliest light in the universe, and the impact of these first galaxies on the high-redshift intergalactic medium. I will then discuss the remarkable new observations by the Hubble Space Telescope of high-redshift galaxies and quasars that probe the predicted epochs of reionization of hydrogen (at a redshift factor z = 7) and singly-ionized helium (at redshift z = 3). We are now learning that the universe was teeming with star-formation activity during its first 500 Myr of existence.

### August 31 — "Nonlinear Waves: What You Wanted to Know but..."

• Presenter: Mark Ablowitz, Applied Math, University of Colorado at Boulder
• Host: Leo Radzihovsky
• Abstract: The study of localized waves has a long history dating back to the discoveries in the 1800s describing water waves in shallow water. In fluid dynamics and nonlinear optics there has been considerable interest in various aspects of localized waves. Perhaps surprisingly, nonlinear waves in water and optics have many similar features. After some introductory and historical remarks, topics that will be briefly discussed include: a novel formulation of classical water waves, some new properties of gravity-capillary waves, ultra-short pulse dynamics in mode-locked lasers and nonlinear waves in photonic graphene'.

### September 7 — "The Biology, Chemistry & Physics of RNA Nano-machines"

• Presenter: Tom Cech, MCDB, University of Colorado at Boulder Director, Colorado Initiative in Molecular Biotechnology Nobel Laureate (Chemistry, 1989)
• Host: Paul Beale
• Abstract: In this colloquium geared for physicists, Prof. Cech will review the fundamental information flow in biology (DNA --> RNA --> Protein) and tell the story of the discovery of catalytic RNA. He will explain how X-ray crystallography has been used to determine atomic structures of catalytic RNA molecules. He will then move to studies of the RNA-protein machine telomerase, which is required to replicate the very ends of chromosomes. Recent work indicates that the RNA once again plays an active role in catalysis, this time helping to move the telomerase template through the active site of the enzyme.

### September 14 — "Unfinished Business in Particle Physics"

• Presenter: Jonathan Rosner, Physics, University of Chicago
• Host: Eric Zimmerman
• Abstract: The past fifty years have seen an incredible consolidation of results in particle physics into a unified picture known as the Standard Model. In one view, only one piece of this puzzle remains - the Higgs boson. I will argue that, on the contrary, we are seeing only the tip of a very large iceberg, with many exciting discoveries to come in the coming decades.

### September 21 — "The Light, and Sound, Fantastic: Radiation Pressure at the Nanoscale"

• Presenter: Oskar Painter, Applied Physics, California Institute of Technology
• Host: Jun Ye
• Abstract: In the last several years, rapid advances have been made in the field of cavity optomechanics, in which the usually feeble radiation pressure force of light is used to manipulate, and precisely monitor, mechanical motion.Amongst the many new geometries studied, coupled phononic and photonic crystal structures (dubbed optomechanical crystals) provide a means for creating integrated, chip-scale, optomechanical systems. Applications of these new nano-opto-mechanical systems include all-optically tunable photonics, optically powered RF and microwave oscillators, and precision force/acceleration and mass sensing. Additionally there is the potential for these systems to be used in hybrid quantum networks, enabling storage or transfer of quantum information between disparate quantum systems. A prerequisite for such quantum applications is the removal of thermal excitations from the low-frequency mechanical oscillator. In this talk I will describe our recent efforts to optically cool and measure the quantum mechanical ground-state of a GHz oscillator (see figure below), and to demonstrate efficient translation between light and sound quanta.

### September 28 — "Tracing Attosecond Dynamics of Electrons in Molecules"

• Presenter: Andreas Becker, Physics, JILA
• Abstract: In the past time-resolved experiments and theoretical analysis explored molecular rotation and vibration as well as chemical reactions on the time scale of atomic motion. Recent advances in laser science led to the development of attosecond laser pulses (1 atomic unit = 24 attoseconds) which can uncover new insights in the inner dynamics of atoms and molecules on the natural time scale of electronic motion. In my talk I will present physical concepts behind attosecond laser technology and my perspective on the current status of attosecond science. I will then discuss ongoing theoretical and experimental efforts to monitor and control the dynamics of an electron in the chemical bond of a molecule, using nature's most simplest molecule as an example.

### October 5 — "Flight of the Fruit Fly: Life at Intermediate Reynolds Numbers"

• Presenter: Itai Cohen, Physics, Cornell University
• Host: Leo Radzihovsky
• Abstract: There comes a time in each of our lives where we grab a thick section of the morning paper, roll it up and set off to do battle with one of nature's most accomplished aviators - the fly. If however, instead of swatting we could magnify our view and experience the world in slow motion we would be privy to a world-class ballet full of graceful figure-eight wing strokes, effortless pirouettes, and astonishing acrobatics. After watching such a magnificent display, who among us could destroy this virtuoso? How do flies produce acrobatic maneuvers with such precision? What control mechanisms do they need to maneuver? More abstractly, what problem are they solving as they fly? Despite pioneering studies of flight control in tethered insects, robotic wing experiments, and fluid dynamics simulations that have revealed basic mechanisms for unsteady force generation during steady flight, the answers to these questions remain elusive. In this talk I will discuss our strategy for investigating these unanswered questions. I will begin by describing our automated apparatus for recording the free flight of fruit flies and a new technique called Hull Reconstruction Motion Tracking (HRMT) for backing out the wing and body kinematics. I will then show that these techniques can be used to reveal the underlying mechanisms for flight maneuvers, wing actuation, and flight stability. Finally, I will comment on the implications of these discoveries for investigations aimed at elucidating the evolution of flight.

### October 12 — "Controlling Molecular Interactions with Electric Fields"

• Presenter: Heather Lewandowski, Physics, JILA, University of Colorado
• Abstract: The process of breaking one chemical bond and forming another is challenging to understand at a quantum mechanical level. This basic understanding is important to any molecular reaction. However, the complicated quantum nature of these processes is difficult to explore experimentally because full control over all degrees of freedom is required. In particular, controlling interactions between cold molecules using external electric and magnetic fields can elucidate the detailed role of quantum mechanics in molecular collisions.
We introduce a versatile platform for investigating atom-molecule interactions at temperatures of 100 mK and demonstrate that an electric field can strongly affect cold atom-molecule collisions. These results show that even when only one of the colliding species is polar, electric fields can have a major effect on the collision dynamics at millikelvin temperatures. These experiments represent a launching pad to understanding and controlling cold chemical reactions.

### October 13 (NOTE: Thursday colloquium, different location) — "Revisiting Blackbody Radiation at the Nanoscale"

• Presenter: Jean-Jacques Greffet, Laboratoire Charles Fabry, Institut d'Optique, CNRS
• Location: JILA Auditorium
• Host: Markus Raschke
• Abstract: When reducing the size of systems down to the nanoscale, usual macroscopic laws are often no longer valid. In this talk, we will show that blackbody radiation is dramatically modified at the nanoscale. We will show that blackbody radiation can be coherent in the near field. We will also show that the energy flux can be orders of magnitude larger than the standard Stefan-Boltzman σT4 law. All these effects cannot be understood in the framework of radiometry. We will briefly discuss how thermal radiation can be described using an electrodynamics framework.

### October 19 — "Results from the CMS Experiment at the LHC"

• Presenter: Kevin Stenson, University of Colorado at Boulder
• Abstract: The Large Hadron Collider has been colliding protons at a world-record energy of 7 TeV for 18 months. The data collected by the four LHC experiments has expanded our understanding of the most fundamental forces of nature. Following a description of the accelerator and experiment, I will present a selection of results from the CMS experiment. These results include searches for the Higgs boson and for new physics such as supersymmetry. I will also provide an outlook of the physics still to come from the LHC as the luminosity and energy increase.

### October 26 — "What if we don't find the Higgs?"

• Presenter: Adam Martin, Fermilab
• Host: Anna Hasenfratz
• Abstract: With the first full year of LHC running nearly over, the Higgs boson has yet to be seen. While there are a few places left where it can hide, they are getting fewer by the day. In this talk I will review the role the Higgs boson plays in the standard model and discuss how the theory can be adjusted to 'hide' the Higgs. These adjustments range from slight tweaks to the Higgs decay channels to removing the Higgs boson completely!

### October 31 (Special Physics Colloquium) — "A Multi-disciplinary Discussion of the CNGS/OPERA Neutrino Speed Anomaly

• Presenters: Alysia Marino, Eric Zimmerman, Neil Ashby, Judah Levine, Physics, University of Colorado Boulder
• Abstract: The apparent greater-than-c speed of neutrinos between the CERN accelerator and LGNS OPERA detector at Gran Sasso in Italy is the subject of enormous interest and attention in the scientific community as well as in the media. This seminar will discuss how the measurements were made, concepts of world-wide clock synchronization using GPS coordinate time, and the details of the time difference measurements made in the experiment.

### November 2 — "Three-Dimensional Magnetic Field Line Reconnection"

• Presenter: Walter Gekelman, Physics, UCLA
• Host: Tobin Munsat
• Abstract: Magnetic field line reconnection is a processes in which magnetic field energy is converted to particle energy and heating accompanied by changes in the magnetic field topology. It occurs near the surface of the sun and is thought to be responsible for coronal heating. Images and data from the sun and several laboratory experiments indicate that reconnection is a fully three-dimensional process. Reconnection events often involve complex structures called magnetic flux ropes, which are helical magnetic fields with pitch that varies with radius. We describe experiments in the 17-meter long large plasma device (LAPD) at UCLA in which up to three magnetic flux ropes are generated from adjacent pulsed current channels. The flux ropes exert mutual magnetic forces causing them to twist about each other and merge, while the currents associated with the ropes exhibit dynamic behavior and break up into filaments following the merging process. Volumetric space-time data show multiple reconnection sites with time-dependent locations. We describe the concept of the quasi-separatrix layer, a tool to understand and visualize how magnetic field lines reconnect in 3D, observed for the first time in our laboratory. Its three dimensional development will be shown in movies made from the data. Other phenomena such as merging of current sheets leading to filamentation will also be presented.
• View the presentation slides (pdf).

### November 9 — "Pairing in Unusual Places — Stretching the Realm of Superconductivity"

• Presenter: Randall Hulet, Physics, Rice University
• Host: Leo Radzihovsky
• Abstract: Ultracold atoms are powerful tools for the investigation of complex many-body phenomena. This is partly a consequence of the ability to vary parameters such as interaction strength and dimensionality. I will discuss experiments on the pairing of spin-polarized 6Li atoms in both 3D and 1D geometries. Spin-polarization of ultracold atoms is accomplished by creating an imbalanced population of two hyperfine levels, a scenario with direct correspondence to magnetized superconductors, and perhaps with the physics of neutron stars. Spin-polarized ultracold atomic gases are excellent candidates for creating the elusive Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) modulated superfluid state, which is characterized by pairs with non-zero center of mass momentum.

### November 16 — "Physics Education Research: A Resource for Educational Transformation at a Critical Time"

• Presenter: Noah Finkelstein, University of Colorado Boulder
• Abstract: After decades of research into student learning, assessments, and curriculum design, physics is considered one of the leading fields engaged in discipline-based educational research (DBER). Simultaneously, unprecedented national attention is now being paid to the outcomes of and needs for DBER. After framing the national scale scene of physics education, and how physics education research (PER) is positioned to contribute to the national dialog, I will review the growth of our own program at CU, and particularly my own research that examines several of the critical scales of focus in physics education. This work develops a new theoretical line of inquiry in PER through experimental work on student reasoning in physics at the level of the individual, the course, and the departmental scales. I will present samples of these scales reviewing: novel work on student use of representation and analogy in physics learning, demonstration of the impacts of teaching interpretive themes on student learning of quantum mechanics in our modern physics courses, and conclude with how subtle faculty choices influence something as canonical as clicker use in our introductory physics sequence.
• View a video of the lecture (part 1 and part 2).

### November 30 — "Einstein's Next Test"

• Presenter: Neil Cornish, Montana State University
• Host: Peter Bender
• Abstract: When Einstein was asked how he would have reacted if Eddington's expedition to measure the bending of light by the Sun had conflicted with the predictions of general relativity, he replied "Then I would feel sorry for the dear Lord. The theory is correct anyway." Over the ensuing century Einstein's theory has survived a wide array of precision experimental tests. In the coming decade the detection of gravitational waves will allow us to test dynamical, strong field gravity for the first time, including such basic predictions that gravitational waves propagate at the speed of light and come in two transverse polarizations, and that black holes have event horizons. In the next five years the advanced LIGO-Virgo detectors will be online, and the galactic scale gravitational wave detector formed by an array of milli-second pulsars should also be sensitive enough to make a detection. Next decade we hope to fly some variant of the space based LISA detector. I will describe how these instruments can be used to perform unique tests of Einstein's theory.

### December 7 — "Search for the Chimera" NOTE LOCATION CHANGE: DUAN G1B30

• Presenter: James Randi, James Randi Educational Foundation
• Host: Leo Radzihovsky
• Abstract: James Randi exposes popularly-accepted fakery by discussing with his audience everything from ESP to dowsing, from academic frauds to faith healers. Randi reveals what really took place in the last three decades in the labs of various prestigious "think tanks" that verified a series of simple magicians tricks as genuine miracles, thus launching a world-wide plague of misinformation, the repercussions of which can still be felt today. This unique and provocative lecture is not only educational but also highly entertaining. It attracts persons of all educational and social backgrounds and provides a rational perspective on the seemingly paranormal and otherwise unexplained happenings in our day-to-day life.