Colloquia are Wednesdays at 4:00 p.m. in the JILA Auditorium. 

Coffee, tea and cookies will be available in G1B31 (across from G1B20) from 3:30 - 3:50 p.m.

August 30 — "Speed limits and locality in many-body quantum dynamics"

  • Presenter: Andrew Lucas, University of Colorado, Boulder
  • Host: Tobin Munsat
  • Abstract: Information cannot travel faster than the speed of light.  Still, in many practical settings (such as listening to sound), emergent speed limits on information can be far slower than the limit set by relativity.  In 1972, Lieb and Robinson proved that quantum correlations and information propagate with a finite velocity in (non-relativistic) quantum many-body spin systems with nearest neighbor interactions.  In practical systems, these speed limits are orders of magnitude smaller than the speed of light.  Five decades later, the Lieb-Robinson Theorem has become one of the most important results in mathematical quantum physics. I will introduce and motivate the Lieb-Robinson Theorem, and overview our recent generalizations of the Lieb-Robinson Theorem to systems with power-law interactions, bosonic models, and dynamics with measurement. These bounds place tight constraints on how fast information can be shuttled through any future quantum computer.  I will then highlight a number of surprising applications of Lieb-Robinson bounds to many-body physics: the computational cost of simulating many-body dynamics on classical and quantum computers, revealing the properties of gapped phases, and proving the existence and metastability of the false vacuum. These results highlight how locality can play a central role in constraining what is possible in quantum systems.

**CANCELED** September 6 — "Benchmarking Quantinuum’s Second-Generation Quantum Processor"

  • Presenter: Steven Moses, Quantinuum
  • Host: Jun Ye
  • Abstract: One of the main challenges facing large-scale quantum computing is scaling systems to more qubits while maintaining high fidelity operations. In this talk, I will describe our efforts at Quantinuum in scaling trapped-ion quantum computers based on the quantum charge-coupled device architecture. We recently released our second-generation machine, which has a race-track shaped ion trap. The new system incorporates several technologies crucial to future scalability, including electrode broadcasting, multi-layer RF routing, and magneto-optical trap loading, while maintaining, and in some cases exceeding, the gate fidelities of our first-generation system. We initially released the system with 32 qubits, but future upgrades will allow for more. I will describe the thorough set of benchmarking experiments we performed to characterize the system, as well as present a selection of recent results of quantum circuits that have been run on the system.

September 13 — "Geometrical approach for designing protected superconducting qubits"

  • Presenter: András Gyenis, Department of Electrical, Computer and Energy Engineering, University of Colorado, Boulder
  • Host: Andrew Lucas
  • Abstract: Quantum-based electronics is an accelerating technology, where information is encoded in the quantum mechanical states of coupled superconducting circuits. To unlock the potential of quantum computers, one of the key challenges that the field has to overcome is to preserve the coherence of a quantum superposition over extended times. Besides implementing quantum error correction schemes, a complementary approach to prolong the coherence of quantum processors is to develop qubits that are intrinsically protected against decoherence. In this talk, we discuss the basic requirements of such protected superconducting qubits, and present a universal method to describe arbitrary quantum circuits based on the connection between symplectic geometry and graph theory. In the second part of the talk, we present preliminary results on how to use disordered superconductors to open the way to building superconducting qubits with protection against information loss. In particular, we focus on elements built from disordered WSi which has shown excellent properties in single photon detectors.

September 20 — "How old are Saturn’s rings?"

  • Presenter: Sascha Kempf, University of Colorado, Boulder
  • Host: Tobin Munsat
  • Abstract: One of the most exciting and controversial aspects of Saturn’s magnificent rings is that they may actually be a recent phenomenon in the solar system – forming long after the Earth, Saturn, and its moon. This possibility has been vigorously debated for nearly 40 years, since the Voyager flybys of Saturn. Over the years, the most powerful support for this hypothesis has turned out to be the puzzle of the rings’ nearly pure water ice composition – unique in the family of planetary rings – in spite of the constant hail of rocky-carbon meteoroids from outside the Saturn system. However, three major uncertainties have left the young-ring hypothesis unproven. Two of these have already been resolved by the Cassini mission: the amount of non-icy material currently in the rings, and the total ring mass. The third main constraint is the mass flux of non-icy meteoroids falling onto the rings. 
    Measuring this mass flux was always a main science goal of the Cassini mission, and could only be achieved by the Cassini Cosmic Dust Analyzer instrument (CDA). In my talk I will report about the determination of the mass flux of non-icy material coming into the Saturn system, which completes the trifecta of constraints that are required to strongly support a youthful ring system. The measurements present a thorough and detailed analysis of the series of unconnected individual particle detections by CDA over Cassini’s entire 13 year mission, converting these detections into the desired mass flux. The CDA detections determine the incident particle orbits, and they come (surprisingly) not from comets as expected, but mostly from Kuiper Belt Objects. This means that most of the particles have low speeds relative to Saturn and are strongly focused gravitationally, such that the flux at the rings is even larger than previously estimated. The derived mass flux implies a ring exposure time of less than 100 to 400 million years, which is in support of recent ring formation scenarios.

September 27 — "The power of plasma: Extending the energy frontier and democratizing X-ray lasers"

  • Presenter: Michael Litos, University of Colorado, Boulder
  • Host: Tobin Munsat
  • Abstract: Plasma-based particle accelerators have transitioned from dream to reality over the past four decades and have approached within striking distance of application readiness. Bunches comprising tens-of-millions of electrons are now regularly accelerated from rest to nearly 10 GeV of energy-per-particle in the distance of mere centimeters. With such accelerating gradients, it should be possible to extend the reach of particle colliders operating at the energy frontier, as well as reduce the size and cost of ultra-high-brightness X-ray laser sources, making them more accessible to researchers throughout the world. One of the next major challenges to the field is the preservation of beam quality before, during, and after the acceleration process to meet the physics-driven demands of the major target applications. In this talk, I will describe efforts being led by my group to address this and other challenges at SLAC National Accelerator Laboratory’s FACET-II plasma wakefield accelerator research facility.

October 4 — "A long quadrucal number--what chromosomes teach us about animal evolution: the legacy of George Gamow"

  • Presenter: Daniel Rokhsar, University of California, Berkeley Department of Molecular and Cellular Biology 
  • Host: Paul Beale
  • NOTE SPECIAL LOCATION: Jennie Smoly Caruthers Biotech Building - Charlie Butcher Auditorium, Room A115
  • Time: 4:00 p.m. (Tea and Cookies available beginning 3:30 p.m.)
  • Abstract: Soon after the discovery of the double helix, George Gamow speculated about how what he called "the number of the beast" — the long information-rich DNA sequence present in chromosomes — might encode the properties of different forms of life. His playful formulation of this central problem in biology, and the "RNATIE Club" that he founded to explore this question, stimulated early thinking about the genetic code long before DNA sequencing was possible. Fast-forwarding seventy years, we can now compare the "long quadrucal numbers" from a wide diversity of species. This talk will explain how such comparisons illuminate key steps in the early evolution of animals that occured over five hundred million years ago. We show that, with a few notable exceptions, animal chromosomes are remarkably stable and evolve slowly over hundreds of millions of years, and that some gene linkages extend even further back in time. We then use these deeply conserved aspects of genome organization to (1) show that ctenophores rather than sponges are the earliest branching lineage of living animals, which has implications for the evolution of nervous systems, and (2) decipher the history of Paleozoic polyploidy and promiscuity in our vertebrate lineage.

October 11

  • Presenter: Eleni Katifori, University of Pennsylvania
  • Host: Andrew Lucas
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October 18

  • Presenter: Umesh Vazirani, University of California, Berkeley, Dept. of Computer Science
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October 25

  • Presenter: Markus Greiner, Harvard University
  • Host: Adam Kaufman
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November 1

  • Presenter: Peter Abbamonte, University of Illinois, Urbana-Champaign 
  • Host: Dan Dessau
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November 8

  • Presenter: Eleni Katifori, University of Pennsylvania
  • Host: Andrew Lucas
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November 15 — "Advancing our understanding of the solar corona by engaging over 1400 students in authentic research"

  • Presenter: Heather Lewandowski, JILA, University of Colorado, Boulder
  • Host: Noah Finkelstein
  • Abstract: Participation in undergraduate research experiences (UREs) has been identified as an important way of increasing undergraduate retention, interest, and identity within the sciences. Course-based undergraduate research experiences (CUREs) have been shown to have similar outcomes to UREs, but can reach a larger number of students at one time and are accessible to any student simply through enrollment in a course. One key component of a CURE is that students must participate in authentic scientific discovery in which they answer a question where the answer is initially unknown to both students and the scientific community. Here, we present student experiences with authentic research in the first large-enrollment, introductory physics CURE conducted remotely during the COVID-19 pandemic. The outcomes of this CURE include a new result suggesting the mechanism for why the sun’s corona is so much hotter than the surface of the sun, which is a longstanding puzzle in solar physics. Additionally, we find that the course helped students gain research skills and programming confidence, engage in productive and enjoyable teamwork experiences, and feel motivated and interested in experimental physics research.

November 22 — No Colloquium, Fall Break 

November 29

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December 6 

  • Presenter: Jorge Noronha, University of Illinois, Urbana-Champaign
  • Host: Andrew Lucas
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December 13

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For more information about colloquia this semester, contact: Andrew Lucas.