## Q-SEnSE

1. M. F. J. Fox , B. M. Zwickl, and H. J. Lewandowski, "Preparing for the quantum revolution: What is the role of higher education?", Physical Review Physics Education Research 16, 020131 (2020), DOI: 10.1103/PhysRevPhysEducRes.16.02013
Quantum sensing, quantum networking and communication, and quantum computing have attracted significant attention recently, as these quantum technologies could offer significant advantages over existing technologies. In order to accelerate the commercialization of these quantum technologies, the workforce must be equipped with the necessary skills. Through a qualitative study of the quantum industry, we describe types of activities being carried out in the quantum industry, profile types of jobs that exist, and describe skills valued across the quantum industry and in each type of job. Current routes into the quantum industry are detailed, profiling the current role of higher education in training a quantum workforce.
2. C. J. Kennedy, E. Oelker, J. M. Robinson, T. Bothwell, D. Kedar, W. R. Milner, G. E. Marti, A. Derevianko, and J. Ye, "Precision Metrology Meets Cosmology: Improved Constraints on on Ultralight Dark Matter from Atom-Cavity Frequency Comparisons", Phys. Rev. Lett. 125, 201302 (2020), DOI 10.1103/PhysRevLett.125.201302
We used three well-established quantum measurement techniques to set new limits on how strongly very low-mass candidates for hypothesized, but so far unobserved, "dark matter" interact with the atoms of regular matter familiar from the world around us. By using cross-comparisons of three measurement techniques, with their different sensitivities to different fundamental constants of Nature, we set tight limits on the properties of one hypothesized type of dark matter and suggest how to expand similar dark matter searches to higher mass. The success of this approach reinforces the trend of using optical light (in or near the visible range) instead of the traditional microwaves to measure time most accurately.
3. K. Matsuda, L. De Marco, J-R. Li, W.G. Tobias, G. Valtolina, G. Quéméner, J. Ye, "Resonant collisional shielding of reactive molecules using electric fields", Science, Vol. 370, Issue 6522, pp. 1324-1327 (2020), DOI: 10.1126/science.abe737
Ultracold gases of molecules offer a promising platform for new explorations in quantum science, but there's a catch: molecules can undergo rapid chemical reactions, severely limiting how long we can observe the interacting quantum system. In this work, we demonstrated a general method to "shield" molecules from chemical reactions by turning on an external electric field. At a particular electric field strength (the "shielding field"), our potassium-rubidium molecules strongly repelled each other at short distances, and as a result, the rate of chemical reactions was highly suppressed. Once shielded from chemical reactions, the molecules survived for ten times longer than at zero electric field, providing an excellent starting point for future experiments.
4. S. Kelly, A. M. Rey, and J. Marino, "Effect of active photons on dynamical frustration in cavity QED", Physical Review Letters 126, 133603 (2021), 10.1103/PhysRevLett.126.133603
We studied the far-from-equilibrium dynamical regimes of a many-body spin-boson model with disordered couplings relevant for cavity QED and trapped ion experiments. Our study illustrated the resilience of glassy-like dynamics in the presence of active photonic degrees of freedom, suggesting that disordered quantum many-body systems with resonant photons or phonons can display a rich diagram of nonequilibrium responses, with near future applications for quantum information science.
5. R. J. Lewis-Swan, D. Barberena, J. R. K. Cline, D. Young, J.K. Thompson, and A. M. Rey, "Cavity-QED quantum simulator of dynamical phases of a BCS superconductor", Phys. Rev. Lett. 126, 173601 (2021), DOI 10.1103/PhysRevLett.126.173601
In a BCS superconductor electrons can overcome their electrostatic repulsion and manage to attract each other forming Cooper pairs. Superconductivity can naturally emerge by slowly modifying the temperature or pressure of special type of materials. However, it has been predicted that superconductivity can also emerge dynamically by abruptly changing the parameters of the system. So far only indirect evidence of these out-of-equilibrium phases exists in recent pump-probe THz experiments. This work proposes a feasible way for the direct observation of dynamical superconductivity in a cavity QED setting where instead of Cooper pairs it is proposed to use atoms with two internal levels interacting via the exchange of photons in an optical cavity. This work demonstrates how the versatility and robustness of a cavity-QED platform not only allows for the exhaustive study of the entire BCS phase diagram, but also enables experiments to study new dynamical phases in regimes inaccessible in real materials
6. T. Bilitewski, L. De Marco, J. Li, K. Matsuda, W. Tobias, G. Valtolina, J. Ye, and A. M. Rey, "Dynamical generation of spin squeezing in ultra-cold dipolar molecules", Phys. Rev. Lett. 126, 113401 (2021). DOI 10.1103/PhysRevLett.126.113401
Creating a quantum gas of dipolar molecules brings new opportunities to explore exotic quantum phenomena. Exploring long-range interactions among molecules confined in reduced spatial dimensions, quantum correlations between rotations of individual molecules can be established, according to the theory model constructed on a realistic experimental platform. This correlation can be used to enhance metrological capabilities for field sensing
7. M. Mamaev, I. Kimchi, R. Nandkishore, and A.M. Rey, "Tunable spin model generation in spin-orbital coupled fermions in optical lattices", Physical Review Research 3, 013178 (2021). DOI 10.1103/PhysRevResearch.3.013178
We study the dynamical behavior of ultracold fermionic atoms loaded into an optical lattice under the presence of an effective magnetic flux, induced by spin-orbit-coupled laser driving. At half-filling, the resulting system can emulate a variety of iconic spin-1/2 models such as an Ising model, an XY model, a generic XXZ model with arbitrary anisotropy, or a collective one-axis twisting model. The validity of these different spin models is examined across the parameter space of flux and driving strength. In addition, there is a parameter regime where the system exhibits chiral, persistent features in the long-time dynamics. We explore these properties and discuss the role played by the system's symmetries. We also discuss experimentally viable implementations.
8. A. Chu, J. Will, J. Arlt, C. Klempt, and A. M. Rey, "Simulation of XXZ Spin Models using Sideband Transitions in Trapped Bosonic Gases", Physical Review Letters 125, 240504 (2020). DOI 10.1103/PhysRevLett.125.240504
We theoretically propose and experimentally demonstrate the use of motional sidebands in a trapped ensemble of ^{87}Rb atoms to engineer tunable long-range XXZ spin models. We benchmark our simulator by probing a ferromagnetic to paramagnetic dynamical phase transition in the Lipkin-Meshkov-Glick model, a collective XXZ model plus additional transverse and longitudinal fields, via Rabi spectroscopy. We experimentally reconstruct the boundary between the dynamical phases, which is in good agreement with mean-field theoretical predictions. Our work introduces new possibilities in quantum simulation of anisotropic spin-spin interactions and quantum metrology enhanced by many-body entanglement.
9. R. J. Lewis-Swan, S.R. Muleady, and A. M. Rey, "Detecting out-of-time-order correlations via quasiadiabatic echoes as a tool to reveal quantum coherence in equilibrium quantum phase transitions", Physical Review Letters 125, 240605 (2020). DOI 10.1103/PhysRevLett.125.240605
We propose a new dynamical method to connect equilibrium quantum phase transitions and quantum coherence using out-of-time-order correlations (OTOCs). Adopting the iconic Lipkin-Meshkov-Glick and transverse-field Ising models as illustrative examples, we show that an abrupt change in coherence and entanglement of the ground state across a quantum phase transition is observable in the spectrum of multiple quantum coherence intensities, which are a special type of OTOC. We also develop a robust protocol to obtain the relevant OTOCs using quasi-adiabatic quenches through the ground state phase diagram. Our scheme allows for the detection of OTOCs without time reversal of coherent dynamics, making it applicable and important for a broad range of current experiments where time reversal cannot be achieved by inverting the sign of the underlying Hamiltonian.
10. M. H. Muñoz-Arias, P. Poggi, and I. Deustch, “Nonlinear dynamics and quantum chaos of a family of kicked p-spin models”, Phys. Rev. E 103, 052212 (2021). DOI 10.1103/PhysRevE.103.052212
We introduce kicked p-spin models describing a family of transverse Ising-like models for an ensemble of spin-1/2 particles with all-to-all p-body interaction terms occurring periodically in time as delta-kicks. This is the natural generalization of the well-studied quantum kicked top (p=2) [Haake, Kuś, and Scharf, Z. Phys. B 65, 381 (1987)]. We fully characterize the classical nonlinear dynamics of these models, including the transition to global Hamiltonian chaos. The classical analysis allows us to build a classification for this family of models, distinguishing between p = 2 and p > 2, and between models with odd and even p's. Quantum chaos in these models is characterized in both kinematic and dynamic signatures. For the latter, we show numerically that the growth rate of the out-of-time-order correlator is dictated by the classical Lyapunov exponent. Finally, we argue that the classification of these models constructed in the classical system applies to the quantum system as well.
11. R.J. Fasano, Y.J. Chen, W.F. McGrew, W.J. Brand, R.W. Fox, and A.D. Ludlow, "Characterization and Suppression of Background Light Shifts in an Optical Lattice Clock", Phys. Rev. Applied 15, 044016 (2021), DOI: 10.1103/PhysRevApplied.15.044016
Experiments involving optical traps often require careful control of the ac Stark shifts induced by strong confining light fields. By carefully balancing light shifts between two atomic states of interest, optical traps at the magic wavelength have been especially effective at suppressing deleterious effects stemming from such shifts. Highlighting the power of this technique, optical clocks today exploit Lamb-Dicke confinement in magic-wavelength optical traps, in some cases realizing shift cancelation at the ten parts per billion level. Theory and empirical measurements can be used at varying levels of precision to determine the magic wavelength where shift cancelation occurs. However, lasers exhibit background spectra from amplified spontaneous emission or other lasing modes that can easily contaminate measurement of the magic wavelength and its reproducibility in other experiments or conditions. Indeed, residual light shifts from laser background have plagued optical lattice clock measurements for years. In this work, we develop a simple theoretical model allowing prediction of light shifts from measured background spectra. We demonstrate good agreement between this model and measurements of the background light shift from an amplified diode laser in a Yb optical lattice clock. Additionally, we model and experimentally characterize the filtering effect of a volume Bragg grating bandpass filter, demonstrating that application of the filter can reduce background light shifts from amplified spontaneous emission well below the $10^{−18}$ fractional clock frequency level. This demonstration is corroborated by direct clock comparisons between a filtered amplified diode laser and a filtered titanium:sapphire laser.
12. R. Lewis-Swan, S. R. Muleady, D. Barberena, J. J. Bollinger, and A. M. Rey, "Characterizing the dynamical phase diagram of the Dicke model via classical and quantum probes", Phys. Rev. Res. 3, L022020 (2021), DOI 10.1103/PhysRevResearch.3.L022020
We theoretically study the dynamical phase diagram of the Dicke model in both classical and quantum limits using large, experimentally relevant system sizes. Our analysis elucidates that the model features dynamical critical points that are strongly influenced by features of chaos and emergent integrability in the model. Moreover, our numerical calculations demonstrate that mean-field features of the dynamics remain valid in the exact quantum dynamics, but we also find that in regimes where quantum effects dominate signatures of the dynamical phases and chaos can persist in purely quantum metrics such as entanglement and correlations. Our predictions can be verified in current quantum simulators of the Dicke model including arrays of trapped ions.
13. A. Cidrim, P. Orioli, C. Sanner, R. B. Hutson, J. Ye, R. Bachelard, and A. M. Rey, "Dipole-dipole frequency shifts in multilevel atoms", Phys. Rev. Lett 127, 013401 (2021), DOI 10.1103/PhysRevLett.127.013401
Dipole-dipole interactions lead to frequency shifts that are expected to limit the performance of next-generation atomic clocks. In this work, we compute dipolar frequency shifts accounting for the intrinsic atomic multilevel structure in standard Ramsey spectroscopy. When interrogating the transitions featuring the smallest Clebsch-Gordan coefficients, we find that a simplified two-level treatment becomes inappropriate, even in the presence of large Zeeman shifts. For these cases, we show a net suppression of dipolar frequency shifts and the emergence of dominant nonclassical effects for experimentally relevant parameters. Our findings are pertinent to current generations of optical lattice and optical tweezer clocks, opening a way to further increase their current accuracy, and thus their potential to probe fundamental and many-body physics.
14. C. D. Marciniak, T. Feldker, I. Pogorelov, R. Kaubruegger, D. V. Vasilyev, R. van Bijnen, P. Schindler, P. Zoller, R. Blatt & T. Monz, "Optimal metrology with programmable quantum sensors", Nature volume 603, pages 604–609 (2022), DOI: 10.1038/s41586-022-04435-4
Quantum sensors are an established technology that has created new opportunities for precision sensing across the breadth of science. Using entanglement for quantum enhancement will allow us to construct the next generation of sensors that can approach the fundamental limits of precision allowed by quantum physics. However, determining how state-of-the-art sensing platforms may be used to converge to these ultimate limits is an outstanding challenge. Here we merge concepts from the field of quantum information processing with metrology, and successfully implement experimentally a programmable quantum sensor operating close to the fundamental limits imposed by the laws of quantum mechanics. We achieve this by using low-depth, parametrized quantum circuits implementing optimal input states and measurement operators for a sensing task on a trapped-ion experiment. With 26 ions, we approach the fundamental sensing limit up to a factor of 1.45 $\pm$ 0.01, outperforming conventional spin-squeezing with a factor of 1.87 $\pm$ 0.03. Our approach reduces the number of averages to reach a given Allan deviation by a factor of 1.59 $\pm$ 0.06 compared with traditional methods not using entanglement-enabled protocols. We further perform on-device quantum-classical feedback optimization to ‘self-calibrate’ the programmable quantum sensor with comparable performance. This ability illustrates that this next generation of quantum sensor can be used without previous knowledge of the device or its noise environment.
15. C. Hughes, D. Finke, D.-A. German, C. Merzbacher, P. M. Vora, and H. J. Lewandowski, "Assessing the Needs of the Quantum Industry", arxiv.org/abs/2109.03601
Quantum information science and technology (QIST) has progressed significantly in the last decade, such that it is no longer solely in the domain of research labs, but is now beginning to be developed for, and applied in, industrial applications and products. With the emergence of this new quantum industry, a new workforce trained in QIST skills and knowledge is needed. To help support education and training of this workforce, universities and colleges require knowledge of the type of jobs available for their students and what skills and degrees are most relevant for those new jobs. Additionally, students need to know how to tailor their degrees to best align with the current needs of the quantum industry. We report on the results from a survey of 57 companies in the quantum industry, with the goal of elucidating the jobs, skills, and degrees that are relevant for this new workforce. We find a range of job opportunities from highly specific jobs, such as quantum algorithm developer and error correction scientist, to broader jobs categories within the business, software, and hardware sectors. These broader jobs require a range of skills, most of which are not quantum related. Further, except for the highly specific jobs, companies that responded to the survey are looking for a range of degree levels to fill these new positions, from bachelors to masters to PhDs. With this knowledge, students, instructors, and university administrators can make informed decisions about how to address the challenge of increasing the future quantum workforce.
16. B. Li, J. Bartos, Y. Xie, and S-W Huang, "Time-magnified photon counting with 550-fs resolution", Optica 8, 1109 (2021) DOI 10.1364/OPTICA.420816
The authors demonstrate a quantum temporal magnifier that enables femtosecond time-resolved photon counting with close-to-unity efficiency for the first time. The new technology can benefit many research fields such as fluorescence lifetime microscopy, time-of-flight imaging, light-in-flight imaging, time-gated Raman spectroscopy, and computational diffuse optical tomography.
17. D. T. C. Allcock, W. C. Campbell, J. Chiaverini, I. L. Chuang, E. R. Hudson, I. D. Moore, A. Ransford, C. Roman, J. M. Sage, and D. J. Wineland, "omg Blueprint for Trapped Ion Quantum Computing with Metastable States", Appl. Phys. Lett. 119, 214002 (2021), DOI: 10.1063/5.0069544
Quantum computers, much like their classical counterparts, will likely benefit from flexible qubit encodings that can be matched to different tasks. For trapped ion quantum processors, a common way to access multiple encodings is to use multiple, co-trapped atomic species. Here, we outline an alternative approach that allows flexible encoding capabilities in single-species systems through the use of long-lived metastable states as an effective, programmable second species. We describe the set of additional trapped ion primitives needed to enable this protocol and show that they are compatible with large-scale systems that are already in operation.
18. K. W. Lehnert, "Quantum enhanced metrology in the search for fundamental physical phenomena", to appear in "Quantum Information Machines; Lecture Notes of the Les Houches Summer School 2019", M. Devoret, B. Huard, and I. Pop editors, SciPost Phys. Lect. Notes 40 (2022), DOI: 10.21468/SciPostPhysLectNotes.40​
These notes summarize lectures given at the 2019 Les Houches summer school on Quantum Information Machines. They describe and review an application of quantum metrology concepts to searches for ultralight dark matter. In particular, for ultralight dark matter that couples as a weak classical force to a laboratory harmonic oscillator, quantum squeezing benefits experiments in which the mass of the dark matter particle is unknown. This benefit is present even if the oscillatory dark matter signal is much more coherent than the harmonic oscillator that it couples to, as is the case for microwave frequency searches for dark matter axion particles.
19. K. Wurtz, B. M. Brubaker, Y. Jiang, E. P. Ruddy, D. A. Palken, and K. W. Lehnert, "A cavity entanglement and state swapping method to accelerate the search for axion dark matter", PRX Quantum 2, 040350 (2021), DOI: 10.1103/PRXQuantum.2.040350
In cavity-based axion dark matter detectors, quantum noise remains a primary barrier to achieving the scan rate necessary for a comprehensive search of axion parameter space. Here we introduce a method of scan rate enhancement in which an axion-sensitive cavity is coupled to an auxiliary resonant circuit through simultaneous two-mode squeezing (entangling) and state swapping interactions. We show analytically that when combined, these interactions can amplify an axion signal before it becomes polluted by vacuum noise introduced by measurement. This internal amplification yields a wider bandwidth of axion sensitivity, increasing the rate at which the detector can search through frequency space. With interaction rates predicted by circuit simulations of this system, we show that this technique can increase the scan rate up to 15-fold relative to the scan rate of a detector limited by vacuum noise.
20. K. Gilmore, M. Affolter, R. J. Lewis-Swan, D. Barberena, E. Jordan, A. M. Rey, and J. J. Bollinger, "Quantum-enhanced sensing of displacements and electric fields with two-dimensional trapped-ion crystals", Science 373(6555), 673–678. (2021), DOI 10.1126/science.abi5226
Fully controllable ultracold atomic systems are creating opportunities for quantum sensing, yet demonstrating a quantum advantage in useful applications by harnessing entanglement remains a challenging task. Here, we realize a many-body quantum-enhanced sensor to detect displacements and electric fields using a crystal of ~150 trapped ions. The center-of-mass vibrational mode of the crystal serves as a high-Q mechanical oscillator, and the collective electronic spin serves as the measurement device. By entangling the oscillator and collective spin and controlling the coherent dynamics via a many-body echo, a displacement is mapped into a spin rotation while avoiding quantum back-action and thermal noise. We achieve a sensitivity to displacements of 8.8 ± 0.4 decibels below the standard quantum limit and a sensitivity for measuring electric fields of 240 ± 10 nanovolts per meter in 1 second. Feasible improvements should enable the use of trapped ions in searches for dark matter.
21. R. Kaubruegger, P. Silvi, C. Kokail, R. van Bijnen, A. M. Rey, J. Ye, A. M. Kaufman, and P. Zoller, "Variational spin-squeezing algorithms on programmable quantum sensors", Phys. Rev. Lett., 123, 260505 (2019), DOI 10.1103/PhysRevLett.123.260505
Arrays of atoms trapped in optical tweezers combine features of programmable analog quantum simulators with atomic quantum sensors. Here we propose variational quantum algorithms, tailored for tweezer arrays as programmable quantum sensors, capable of generating entangled states on demand for precision metrology. The scheme is designed to generate metrological enhancement by optimizing it in a feedback loop on the quantum device itself, thus preparing the best entangled states given the available quantum resources. We apply our ideas to the generation of spin-squeezed states on Sr atom tweezer arrays, where finite-range interactions are generated through Rydberg dressing. The complexity of experimental variational optimization of our quantum circuits is expected to scale favorably with system size. We numerically show our approach to be robust to noise, and surpassing known protocols.
22. M. A. Perlin, D. Barberena, M. Mamaev, B. Sundar, R. J. Lewis-Swan, and A. M. Rey, "Engineering infinite-range SU(n) interactions with spin-orbit-coupled fermions in an optical lattice", Phys. Rev. A. 105(2), 023326 (2022), DOI: 10.1103/PhysRevA.105.023326
We study multilevel fermions in an optical lattice described by the Hubbard model with on site SU(n)-symmetric interactions. We show that in an appropriate parameter regime this system can be mapped onto a spin model with all-to-all SU(n)-symmetric couplings. Raman pulses that address internal spin states modify the atomic dispersion relation and induce spin-orbit coupling, which can act as a synthetic inhomogeneous magnetic field that competes with the SU(n) exchange interactions. We investigate the mean-field dynamical phase diagram of the resulting model as a function of n and different initial configurations that are accessible with Raman pulses. Consistent with previous studies for n=2, we find that for some initial states the spin model exhibits two distinct dynamical phases that obey simple scaling relations with n. Moreover, for n${>}$2 we find that dynamical behavior can be highly sensitive to initial intra-spin coherences. Our predictions are readily testable in current experiments with ultracold alkaline-earth(-like) atoms.
23. T. Bilitewski, A. Pineiro Orioli, C. Sanner, L. Sonderhouse, R. B. Hutson, L. Yan, W. R. Milner, J. Ye, and A. M. Rey, "Disentangling Pauli blocking of atomic decay from cooperative radiation and atomic motion in a 2D Fermi gas", Phys. Rev. Lett. 128(9), 093001 (2022) DOI: 10.1103/physrevlett.128.093001
The observation of Pauli blocking of atomic spontaneous decay via direct measurements of the atomic population requires the use of long-lived atomic gases where quantum statistics, atom recoil, and cooperative radiative processes are all relevant. We develop a theoretical framework capable of simultaneously accounting for all these effects in the many-body quantum degenerate regime. We apply it to atoms in a single 2D pancake or arrays of pancakes featuring an effective ${\Lambda}$ level structure (one excited and two degenerate ground states). We identify a parameter window in which a factor of 2 extension in the atomic lifetime clearly attributable to Pauli blocking should be experimentally observable in deeply degenerate gases with \sim ${10^3}$ atoms. We experimentally observe a suppressed excited-state decay rate, fully consistent with the theory prediction of an enhanced excited-state lifetime, on the ${^{1}S_{0}} - {^{3}P_{1}}$ transition in ${^{87}}$Sr atoms.
24. A. Pineiro Orioli, J. K. Thompson, A. M. Rey, "Emergent dark states from superradiant dynamics in multilevel atoms in a cavity", Phys. Rev. X 12, 011054, (2022), DOI: 10.1103/PhysRevX.12.011054
When atoms are placed inside a cavity, the cavity light mediates collective interactions between atoms at arbitrary distances. For two-level atoms, these collective interactions typically lead to superradiance—a phenomenon whereby atoms cooperate to emit light at an enhanced rate compared to a single atom. Here, we show that atoms with multiple internal levels instead give rise to dark subradiant states, where emission into the cavity is collectively suppressed. Because of their long lifetimes, subradiant states are useful for a wide range of quantum technological applications, but, so far, their actual creation has been challenging since they often require very short interparticle distances not easily achievable in current experiments. The physics of multilevel atoms inside cavities has remained severely underexplored. The main difficulty arises from the fact that multilevel atoms possess multiple transitions, which can couple to the two possible polarizations of light inside a cavity. However, we show that this additional layer of complexity allows multilevel atoms inside cavities to give rise to a plethora of entangled dark states, which are immune to cavity decay because of destructive interference between the light emitted by different internal transitions. These dark states are amenable to experimental observation since they naturally emerge during the superradiant decay path of initially excited atoms in a cavity: Atoms just get stuck in one of these dark states. Our findings open the door to the preparation of entangled dark states of matter through collective dissipation, which are useful for quantum sensing and quantum simulation.
25. J. Huber, A. M. Rey, P. Rabi, "Realistic simulations of spin squeezing and cooperative coupling effects in large ensembles of interacting two-level systems", Phys. Rev. A 105(1), 013716 (2022), DOI: 10.1103/PhysRevA.105.013716
We describe an efficient numerical method for simulating the dynamics of interacting spin ensembles in the presence of dephasing and decay. The method builds on the discrete truncated Wigner approximation for isolated systems, which combines the mean-field dynamics of a spin ensemble with a Monte Carlo sampling of discrete initial spin values to account for quantum correlations. Here we show how this approach can be generalized for dissipative spin systems by replacing the deterministic mean-field evolution by a stochastic process, which describes the decay of coherences and populations while preserving the length of each spin. We demonstrate the application of this technique for simulating nonclassical spin-squeezing effects or the dynamics and steady states of cavity QED models with ${10^5}$ interacting two-level systems. This opens up the possibility to perform accurate real-scale simulations of a diverse range of experiments in quantum optics or with solid-state spin ensembles under realistic laboratory conditions.
26. A. Chu, P. He, J. K. Thompson, A. M. Rey, "Quantum enhanced cavity QED interferometer with partially delocalized atoms in lattices", Phys. Rev. Lett. 127, 210401 (2021), DOI: 10.1103/PhysRevLett.127.210401
We propose a quantum enhanced interferometric protocol for gravimetry and force sensing using cold atoms in an optical lattice supported by a standing-wave cavity. By loading the atoms in partially delocalized Wannier-Stark states, it is possible to cancel the undesirable inhomogeneities arising from the mismatch between the lattice and cavity fields and to generate spin squeezed states via a uniform one-axis twisting model. The quantum enhanced sensitivity of the states is combined with the subsequent application of a compound pulse sequence that allows to separate atoms by several lattice sites. This, together with the capability to load small atomic clouds in the lattice at micrometric distances from a surface, make our setup ideal for sensing short-range forces. We show that for arrays of $10^{4}$ atoms, our protocol can reduce the required averaging time by a factor of 10 compared to unentangled lattice-based interferometers after accounting for primary sources of decoherence.
27. C. Sanner, L. Sonderhouse, R. B. Hutson, L. Yan, W R. Milner, and J. Ye, "Pauli blocking of atom-light scattering", Science Vol 374, Issue 6570, pp. 979-983 (2021), DOI: 10.1126/science.abh348
Transition rates between coupled states in a quantum system depend on the density of available final states. The radiative decay of an excited atomic state has been suppressed by reducing the density of electromagnetic vacuum modes near the atomic transition. Likewise, reducing the density of available momentum modes of the atomic motion when it is embedded inside a Fermi sea will suppress spontaneous emission and photon scattering rates. Here we report the experimental demonstration of suppressed light scattering in a quantum degenerate Fermi gas. We systematically measured the dependence of the suppression factor on the temperature and Fermi energy of a strontium quantum gas and achieved suppression of scattering rates by up to a factor of 2 compared with a thermal gas.
28. S. Omanakuttan, A. Mitra, M. J. Martin, and I. H. Deutsch, "Quantum optimal control of ten-level nuclear spin qudits in 87Sr", Phys. Rev. A 104, L060401 (2021), DOI: 10.1103/PhysRevA.104.L060401
We study the ability to implement unitary maps on states of the I = 9/2 nuclear spin in $^{87}$Sr, a d=10 dimensional (qudecimal) Hilbert space, using quantum optimal control. Through a combination of nuclear spin resonance and a tensor ac Stark shift, by solely modulating the phase of a radio-frequency magnetic field, the system is quantum controllable. Alkaline-earth-metal atoms, such as $^{87}$Sr, have a very favorable figure of merit for such control due to narrow intercombination lines and the large hyperfine splitting in the excited states. We numerically study the quantum speed limit, optimal parameters, and the fidelity of arbitrary state preparation and full SU(10) maps, including the presence of decoherence due to optical pumping induced by the light-shifting laser. We also study the use of robust control to mitigate some dephasing due to inhomogeneities in the light shift. We find that with an rf Rabi frequency of $\Omega_{rf}$ and 0.5$\%$ inhomogeneity in the the light shift we can prepare an arbitrary Haar-random state in a time $T = \frac{4.5\pi}{\Omega_{rf}}$ with average fidelity $$= 0.9992, and an arbitrary Haar-random SU(10) map in a time T = \frac{24\pi}{\Omega_{rf}} with average fidelity$$ = 0.9923.
29. S. B. Jäger, H. Liu, J. Cooper, M. J. Holland, "Collective emission of an atomic beam into an off-resonant cavity mode”, Phys. Rev. A 104, 053705 (2021), DOI: 10.1103/PhysRevA.104.053705
We study the collective emission of a beam of atomic dipoles into an optical cavity. Our focus lies on the effect of a finite detuning between the atomic transition frequency and the cavity resonance frequency. By developing a theoretical description of the coupled atom-cavity dynamics we analyze the stationary atomic configurations including a superradiant phase where the atoms undergo continuous monochromatic collective emission. In addition, we derive an analytical formula for the cavity pulling coefficient which characterizes the displacement of the emission frequency towards the cavity frequency. We find that the pulling is small if the cavity linewidth is much larger than the collective linewidth of the atomic beam. This regime is desired for building stable lasers because the emission frequency is robust against cavity length fluctuations. Furthermore, we investigate the stability of the atomic phases and compare our theoretical predictions with numerical results. Remarkably, we also find polychromatic emission regimes, where the spectrum has several frequency components while the light output is still superradiant.
30. L-Y Chih, M. J. Holland, "Reinforcement-learning-based matter-wave interferometer in a shaken optical lattice”, Physical Review Research 3, 033279 (2021), DOI: 10.1103/PhysRevResearch.3.033279
We demonstrate the design of a matter-wave interferometer to measure acceleration in one dimension with high precision. The system we base this on consists of ultracold atoms in an optical lattice potential created by interfering laser beams. Our approach uses reinforcement learning, a branch of machine learning that generates the protocols needed to realize lattice-based analogs of optical components including a beam splitter, a mirror, and a recombiner. The performance of these components is evaluated by comparison with their optical analogs. The interferometer's sensitivity to acceleration is quantitatively evaluated using a Bayesian statistical approach. We find the sensitivity to surpass that of standard Bragg interferometry, demonstrating the future potential for this design methodology.
31. S. B. Jäger, H. Liu, J. Cooper, T. L. Nicholson, M. J. Holland, "Superradiant emission of a thermal atomic beam into an optical cavity”, Phys. Rev. A 104, 033711 (2021), DOI: 10.1103/PhysRevA.104.033711
We theoretically analyze the collective dynamics of a thermal beam of atomic dipoles that couple to a single mode when traversing an optical cavity. For this setup we derive a semiclassical model and determine the onset of superradiant emission and its stability. We derive analytical expressions for the linewidth of the emitted light and compare them with numerical simulations. In addition, we find and predict two different superradiant phases; a steady-state superradiant phase and a multicomponent superradiant phase. In the latter case we observe sidebands in the frequency spectrum that can be calculated using a stability analysis of the amplitude mode of the collective dipole. We show that both superradiant phases are robust against free-space spontaneous emission and T2 dephasing processes.
32. A. Shankar, J. T. Reilly, S. B. Jäger, and M. J. Holland, "Subradiant-to-Subradiant Phase Transition in the Bad Cavity Laser”, Phys. Rev. Lett. 127, 073603 (2021), DOI: 10.1103/PhysRevLett.127.073603
We show that the onset of steady-state superradiance in a bad cavity laser is preceded by a dissipative phase transition between two distinct phases of steady-state subradiance. The transition is marked by a nonanalytic behavior of the cavity output power and the mean atomic inversion, as well as a discontinuity in the variance of the collective atomic inversion. In particular, for repump rates below a critical value, the cavity output power is strongly suppressed and does not increase with the atom number, while it scales linearly with atom number above this value. Remarkably, we find that the atoms are in a macroscopically entangled steady state near the critical region with a vanishing fraction of unentangled atoms in the large atom number limit.
33. S. B. Jäger, H. Liu, A. Shankar, J. Cooper, M. J. Holland, "Regular and bistable steady-state superradiant phases of an atomic beam traversing an optical cavity”, Phys. Rev. A 103, 013720 (2021), DOI: 10.1103/PhysRevA.103.013720
We investigate the different photon emission regimes created by a pre-excited and collimated atomic beam passing through a single mode of an optical cavity. In the regime where the cavity degrees of freedom can be adiabatically eliminated, we find that the atoms undergo superradiant emission when the collective linewidth exceeds the transit-time broadening. We analyze the case where the atomic beam direction is slanted with respect to the cavity axis. For this situation, we find that a phase of continuous light emission similar to steady-state superradiance is established providing the tilt of the atomic beam is sufficiently small. However, if the atoms travel more than half a wavelength along the cavity axis during one transit time we predict a dynamical phase transition to a bistable superradiant regime. In this phase the atoms undergo collective spontaneous emission with a frequency that can be either blue or red detuned from the free-space atomic resonance. We analyze the different superradiant regimes and the quantum critical crossover boundaries. In particular we find the spectrum of the emitted light and show that the linewidth exhibits features of a critical scaling close to the phase boundaries.
34. H. Liu, S. B. Jäger, X. Yu, S. Touzard, A. Shankar, M. J. Holland, T. L. Nicholson, "Rugged mhz-linewidth superradiant laser driven by a hot atomic beam”, Phys. Rev. Lett. 125, 253602 (2020), DOI: 10.1103/PhysRevLett.125.253602
We propose a new type of superradiant laser based on a hot atomic beam traversing an optical cavity. We show that the theoretical minimum linewidth and maximum power are competitive with the best ultracoherent clock lasers. Also, our system operates naturally in continuous wave mode, which has been elusive for superradiant lasers so far. Unlike existing ultracoherent lasers, our design is simple and rugged. This makes it a candidate for the first widely accessible ultracoherent laser, as well as the first to realize sought-after applications of ultracoherent lasers in challenging environments.
35. W.G. Tobias, K. Matsuda, J-R. Li, C. Miller, A. N. Carroll, T. Bilitewski, A. M. Rey, J. Ye, "Reactions between layer-resolved molecules mediated by dipolar spin exchange", Science, 375, p1299-1303 (2022) , DOI: 10.1126/science.abn8525
Microscopic control over polar molecules with tunable interactions enables the realization of distinct quantum phenomena. Using an electric field gradient, we demonstrated layer-resolved state preparation and imaging of ultracold potassium-rubidium molecules confined to two-dimensional planes in an optical lattice. The rotational coherence was maximized by rotating the electric field relative to the light polarization for state-insensitive trapping. Spatially separated molecules in adjacent layers interact through dipolar spin exchange of rotational angular momentum; by adjusting these interactions, we regulated the local chemical reaction rate. The resonance width of the exchange process vastly exceeded the dipolar interaction energy, an effect attributed to thermal energy. This work realized precise control of interacting molecules, enabling electric field microscopy on subwavelength scales and allowing access to unexplored physics in two-dimensional systems.
36. C. D. Marciniak, T. Feldker, I. Pogorelov, R. Kaubruegger, D. V. Vasilyev, R. van Bijnen, P. Schindler, P. Zoller, R. Blatt, and T. Monz, "Optimal metrology with programmable quantum sensors", Nature 603, 604–609 (2022), DOI: 10.1038/s41586-022-04435-4
Quantum sensors are an established technology that has created new opportunities for precision sensing across the breadth of science. Using entanglement for quantum enhancement will allow us to construct the next generation of sensors that can approach the fundamental limits of precision allowed by quantum physics. However, determining how state-of-the-art sensing platforms may be used to converge to these ultimate limits is an outstanding challenge. Here we merge concepts from the field of quantum information processing with metrology, and successfully implement experimentally a programmable quantum sensor operating close to the fundamental limits imposed by the laws of quantum mechanics. We achieve this by using low-depth, parametrized quantum circuits implementing optimal input states and measurement operators for a sensing task on a trapped-ion experiment. With 26 ions, we approach the fundamental sensing limit up to a factor of 1.45 $\pm$ 0.01, outperforming conventional spin-squeezing with a factor of 1.87 $\pm$ 0.03. Our approach reduces the number of averages to reach a given Allan deviation by a factor of 1.59 $\pm$ 0.06 compared with traditional methods not using entanglement-enabled protocols. We further perform on-device quantum-classical feedback optimization to ‘self-calibrate’ the programmable quantum sensor with comparable performance. This ability illustrates that this next generation of quantum sensor can be used without previous knowledge of the device or its noise environment.
37. T-W Hsu, W. Zhu, T. Thiele, M. O. Brown, S. B. Papp, A. Agrawal, and C. A. Regal, "Single atom trapping in a metasurface lens optical tweezer", PRX Quantum 3, 030316, DOI: 10.1103/PRXQuantum.3.030316
Optical metasurfaces of subwavelength pillars have provided new capabilities for the versatile definition of the amplitude, phase, and polarization of light. In this work, we demonstrate that an efficient dielectric metasurface lens can be used to trap and image single neutral atoms with a long working distance from the lens of 3 mm. We characterize the high-numerical-aperture optical tweezers using the trapped atoms and compare with numerical computations of the metasurface-lens performance. We predict that future metasurfaces for atom trapping will be able to leverage multiple ongoing developments in metasurface design and enable multifunctional control in complex quantum information experiments with neutral-atom arrays.
38. M. O. Brown, S. R. Muleady, W. J. Dworschack, R. J. Lewis-Swan, A. M. Rey, O. Romero-Isart, and C. A. Regal, "Time-of-Flight Quantum Tomography of Single Atom Motion", PRX Quantum 3, 030316, DOI: 10.1103/PRXQuantum.3.030316​
Time of flight is an intuitive way to determine the velocity of particles and lies at the heart of many capabilities ranging from mass spectrometry to fluid flow measurements. Here we show time-of-flight imaging can realize tomography of a quantum state of motion of a single trapped atom. Tomography of motion requires studying the phase space spanned by both position and momentum. By combining time-of-flight imaging with coherent evolution of the atom in an optical tweezer trap, we are able to access arbitrary quadratures in phase space without relying on coupling to a spin degree of freedom. To create non-classical motional states, we harness quantum tunneling in the versatile potential landscape of optical tweezers, and our tomography both demonstrates Wigner function negativity and assesses coherence of non-stationary states. Our demonstrated tomography concept has wide applicability to a range of particles and will enable characterization of non-classical states of more complex systems or massive dielectric particles.
39. A. Asfaw, A. Blais, K. R. Brown, J. Candelaria, C. Cantwell, L. D. Carr, J. Combes, D. M. Debroy, J. M. Donohue, S. E. Economou, E. Edwards, M. F. J. Fox, S. M. Girvin, A. Ho, H. M. Hurst, J. Zubin, B. R. Johnson, E. Johnston-Halperin, R. Joynt, E. Kapit, J. Klein-Seetharaman, M. Laforest, H. J. Lewandowski, T. W. Lynn, C. R. H. McRae, C. Merzbacher, S. Michalakis, P. Narang, W. D. Oliver, J. Palsberg, D. P. Pappas, M. G. Raymer, D. J. Reilly, M. Saffman, T. A. Searles, J. H. Shapiro, and C. Singh, "Building a Quantum Engineering Undergraduate Program", IEEE Transactions on Education 1-23  (2022), DOI: 10.1109/TE.2022.3144943
Contribution: A roadmap is provided for building a quantum engineering education program to satisfy U.S. national and international workforce needs. Background: The rapidly growing quantum information science and engineering (QISE) industry will require both quantum-aware and quantum-proficient engineers at the bachelor's level. Research Question: What is the best way to provide a flexible framework that can be tailored for the full academic ecosystem? Methodology: A workshop of 480 QISE researchers from across academia, government, industry, and national laboratories was convened to draw on best practices; representative authors developed this roadmap. Findings: 1) For quantum-aware engineers, design of a first quantum engineering course, accessible to all STEM students, is described; 2) for the education and training of quantum-proficient engineers, both a quantum engineering minor accessible to all STEM majors, and a quantum track directly integrated into individual engineering majors are detailed, requiring only three to four newly developed courses complementing existing STEM classes; 3) a conceptual QISE course for implementation at any postsecondary institution, including community colleges and military schools, is delineated; 4) QISE presents extraordinary opportunities to work toward rectifying issues of inclusivity and equity that continue to be pervasive within engineering. A plan to do so is presented, as well as how quantum engineering education offers an excellent set of education research opportunities; and 5) a hands-on training plan on quantum hardware is outlined, a key component of any quantum engineering program, with a variety of technologies, including optics, atoms and ions, cryogenic and solid-state technologies, nanofabrication, and control and readout electronics.
40. A. Derevianko, K. Gibble, L. Hollberg, N. R. Newbury, C. Oates, M. S. Safronova, L. C. Sinclair, N. Yu, "Fundamental Physics with a State-of-the-Art Optical Clock in Space", submitted to Quantum Science and Technology (2022), DOI: 10.48550/arXiv.2112.10817
Recent advances in optical atomic clocks and optical time transfer have enabled new possibilities in precision metrology for both tests of fundamental physics and timing applications. Here we describe a space mission concept that would place a state-of-the-art optical atomic clock in an eccentric orbit around Earth. A high stability laser link would connect the relative time, range, and velocity of the orbiting spacecraft to earthbound stations. The primary goal for this mission would be to test the gravitational redshift, a classical test of general relativity, with a sensitivity 30,000 times beyond current limits. Additional science objectives include other tests of relativity, enhanced searches for dark matter and drifts in fundamental constants, and establishing a high accuracy international time/geodesic reference.
41. SpaceQ - Direct Detection of Ultralight Dark Matter with Space Quantum Sensors, Y-D. Tsai, J. Eby, M. S. Safronova, submitted to Nature Astronomy (2022). DOI: 10.48550/arXiv.2112.07674
Recent advances in quantum sensors, including atomic clocks, enable searches for a broad range of dark matter candidates. The question of the dark matter distribution in the Solar system critically affects the reach of dark matter direct detection experiments. Partly motivated by the NASA Deep Space Atomic Clock (DSAC), we show that space quantum sensors present new opportunities for ultralight dark matter searches, especially for dark matter states bound to the Sun. We show that space quantum sensors can probe unexplored parameter space of ultralight dark matter, covering theoretical relaxion targets motivated by naturalness and Higgs mixing. If an atomic clock were able to make measurements on the interior of the solar system, it could probe this highly sensitive region directly and set very strong constraints on the existence of such a bound-state halo in our solar system. We present sensitivity projections for space-based probes of ultralight dark matter which couples to electron, photon, and gluon fields, based on current and future atomic, molecular, and nuclear clocks.
42. T. Bilitewski, A. Piñeiro Orioli, C. Sanner, L. Sonderhouse, R. B. Hutson, L. Yan, W. R. Milner, J. Ye, and A. M. Rey, "Disentangling Pauli Blocking of Atomic Decay from Cooperative Radiation and Atomic Motion in a 2D Fermi Gas", Phys. Rev. Lett. 128, 093001 (2022), DOI: 10.1103/PhysRevLett.128.093001
The observation of Pauli blocking of atomic spontaneous decay via direct measurements of the atomic population requires the use of long-lived atomic gases where quantum statistics, atom recoil, and cooperative radiative processes are all relevant. We develop a theoretical framework capable of simultaneously accounting for all these effects in the many-body quantum degenerate regime. We apply it to atoms in a single 2D pancake or arrays of pancakes featuring an effective ${\Lambda}$ level structure (one excited and two degenerate ground states). We identify a parameter window in which a factor of 2 extension in the atomic lifetime clearly attributable to Pauli blocking should be experimentally observable in deeply degenerate gases with  \sim ${10^3}$ atoms. We experimentally observe a suppressed excited-state decay rate, fully consistent with the theory prediction of an enhanced excited-state lifetime, on the $^{1}S_{0}$ - $^{3}P_{1}$ transition in ${^{87}}Sr$ atoms.
43. Z. Lasner, A. Lunstad, C. Zhang, L. Cheng, J. M. Doyle, "Vibronic branching ratios for nearly-closed rapid photon cycling of SrOH", Phys. Rev. A 106, L020801 – Published 3 August 2022, DOI: 10.1103/PhysRevA.106.L020801
The vibrational branching ratios of SrOH for radiative decay to the ground electronic state, ${X^{2}\Sigma^{+}}$, from the first two electronically excited states, ${A^{2}\Pi}$ and ${B^{2}\Sigma^{+}}$, are determined experimentally at the \sym ${10^{-5}}$  level. The observed small branching ratios enable the design of a full, practical laser-cooling scheme, including magneto-optical trapping and sub-Doppler laser cooling, with $> 10^{4}$ photon scatters per molecule. Ab initio calculations sensitive to weak vibronic transitions are performed to facilitate the experimental measurement and analysis, and show good agreement with experiment.
44. A. Aeppli, A. Chu, T. Bothwell, C. J. Kennedy, D. Kedar, P. He, A. M. Rey, and J. Ye, "Hamiltonian engineering of spin-orbit coupled fermions in a Wannier-Stark optical lattice clock", DOI: 10.48550/arXiv.2201.05909
Engineering a Hamiltonian system with tunable interactions provides opportunities to optimize performance for quantum sensing and explore emerging phenomena of many-body systems. An optical lattice clock based on partially delocalized Wannier-Stark states in a gravity-tilted shallow lattice supports superior quantum coherence and adjustable interactions via spin-orbit coupling, thus presenting a powerful spin model realization. The relative strength of the on-site and off-site interactions can be tuned to achieve a zero density shift at a 'magic' lattice depth. This mechanism, together with a large number of atoms, enables the demonstration of the most stable atomic clock while minimizing a key systematic uncertainty related to atomic density. Interactions can also be maximized by driving off-site Wannier-Stark transitions, realizing a ferromagnetic to paramagnetic dynamical phase transition.
45. B. Sundar, D. Barberena, A. Piñeiro Orioli, A. Chu, J. K. Thompson, A. M. Rey, and R. J. Lewis-Swan, "Bosonic pair production and squeezing for optical phase measurements in long-lived dipoles coupled to a cavity", DOI: 10.48550/arXiv.2204.13090
We propose to simulate bosonic pair creation using large arrays of long-lived dipoles with multilevel internal structure coupled to an undriven optical cavity. Entanglement between the atoms, generated by the exchange of virtual photons through a common cavity mode, grows exponentially fast and is described by two-mode squeezing (TMS) of effective bosonic quadratures. The mapping between an effective bosonic model and the natural spin description of the dipoles allows us to realize the analog of optical homodyne measurements via straightforward global rotations and population measurements of the electronic states, and we propose to exploit this for quantum-enhanced sensing of an optical phase (common and differential between two ensembles). We discuss a specific implementation based on Sr atoms and show that our sensing protocol is robust to sources of decoherence intrinsic to cavity platforms. Our proposal can open unique opportunities for the observation of continuous variable entanglement in atomic systems and associated applications in next-generation optical atomic clocks.
46. C. Overstreet, P. Asenbaum, J. Curti, M. Kim, and M. A. Kasevich, “Observation of a Gravitational Aharonov-Bohm Effect.” Science 375, no. 6577 (January 14, 2022): 226–29, DOI: 10.1126/science.abl7152
The Aharonov-Bohm effect is a quantum mechanical effect in which a magnetic field affects the phase of an electron wave as it propagates along a wire. Atom interferometry exploits the wave characteristic of atoms to measure tiny differences in phase as they take different paths through the arms of an interferometer. Overstreet et al. split a cloud of cold rubidium atoms into two atomic wave packets about 25 centimeters apart and subjected one of the wave packets to gravitational interaction with a large mass (see the Perspective by Roura). The authors state that the observed phase shift is consistent with a gravitational Aharonov-Bohm effect.
47. B. K. Malia, Y. Wu, J. Martínez-Rincón, M. A. Kasevich, "Distributed quantum sensing with a mode-entangled network of spin-squeezed atomic states", DOI: 10.48550/arXiv.2205.06382
Quantum sensors are used for precision timekeeping, field sensing, and quantum communication. Comparisons among a distributed network of these sensors are capable of, for example, synchronizing clocks at different locations. The performance of a sensor network is limited by technical challenges as well as the inherent noise associated with the quantum states used to realize the network. For networks with only local entanglement at each node, the noise performance of the network improves at best with square root of the number of nodes. Here, we demonstrate that nonlocal entanglement between network nodes offers better scaling with network size. A shared quantum nondemolition measurement entangles a clock network with up to four nodes. This network provides up to 4.5 dB better precision than one without nonlocal entanglement, and 11.6 dB improvement as compared to a network of sensors operating at the quantum projection noise limit. We demonstrate the generality of the approach with atomic clock and atomic interferometer protocols, in scientific and technologically relevant configurations optimized for intrinsically differential comparisons of sensor outputs.
48. M. E. Kim, W. F. McGrew, N. V. Nardelli, E. R. Clements, Y. S. Hassan, X. Zhang, J. L. Valencia, H. Leopardi, D. B. Hume, T. M. Fortier, A. D. Ludlow, D. R. Leibrandt, "Optical coherence between atomic species at the second scale: improved clock comparisons via differential spectroscopy", (September, 2021), DOI: 10.48550/arXiv.2109.09540
Comparisons of high-accuracy optical atomic clocks [Ludlow, 2015] are essential for precision tests of fundamental physics [Safronova, 2018], relativistic geodesy [McGrew, 2018; Grotti, 2018; Delva, 2019], and the anticipated redefinition of the SI second [Riehle, 2018]. The scientific reach of these applications is restricted by the statistical precision of interspecies comparison measurements. The instability of individual clocks is limited by the finite coherence time of the optical local oscillator (OLO), which bounds the maximum atomic interrogation time. In this letter, we experimentally demonstrate differential spectroscopy [Hume, 2016], a comparison protocol that enables interrogating beyond the OLO coherence time. By phase-coherently linking a zero-dead-time (ZDT) [Schioppo, 2017] Yb optical lattice clock with an Al$^+$ single-ion clock via an optical frequency comb and performing synchronised Ramsey spectroscopy, we show an improvement in comparison instability relative to our previous result [network2020 frequency] of nearly an order of magnitude. To our knowledge, this result represents the most stable interspecies clock comparison to date.
49. D. R. Leibrandt, S. G. Porsev, C. Cheung, M. S. Safronova, "Prospects of a thousand-ion Sn2+ Coulomb-crystal clock with sub-10^(−19) inaccuracy", (May, 2022), DOI: 10.48550/arXiv.2205.15484
We propose a many-ion optical atomic clock based on three-dimensional Coulomb crystals of order one thousand Sn$^{2+}$ ions confined in a linear RF Paul trap. Sn$^{2+}$ has a unique combination of features that is not available in previously considered ions: a $^{1}S_{0}$ $\leftrightarrow$ $^{3}P_{0}$ clock transition between two states with zero electronic and nuclear angular momentum (I = J = F = 0) making it immune to nonscalar perturbations, a negative differential polarizability making it possible to operate the trap in a manner such that the two dominant shifts for three-dimensional ion crystals cancel each other, and a laser-accessible transition suitable for direct laser cooling and state readout. We present analytical calculations of the differential polarizability and other relevant atomic properties, as well as numerical calculations of the motion of ions in large Coulomb crystals, to estimate the achievable accuracy and precision of Sn$^{2+}$ Coulomb-crystal clocks.
50. E. D. Caldwell, L. C. Sinclair, N. R. Newbury, and J-D Deschenes, "The Time Programmable Frequency Comb: Generation and Application to Quantum-Limited Dual-Comb Ranging", DOI: 10.48550/arXiv.2205.01147
The classic self-referenced frequency comb acts as an unrivaled ruler for precision optical metrology in both time and frequency. Two decades after its invention, the frequency comb is now used in numerous active sensing applications. Many of these applications, however, are limited by the tradeoffs inherent in the rigidity of the comb output and operate far from quantum-limited sensitivity. Here we demonstrate an agile programmable frequency comb where the pulse time and phase are digitally controlled with +/- 2 attosecond accuracy. This agility enables quantum-limited sensitivity in sensing applications since the programmable comb can be configured to coherently track weak returning pulse trains at the shot-noise limit. To highlight its capabilities, we use this programmable comb in a ranging system, reducing the detection threshold by ~5,000-fold to enable nearly quantum-limited ranging at mean pulse photon number of 1/77 while retaining the full accuracy and precision of a rigid frequency comb. Beyond ranging and imaging, applications in time/frequency metrology, comb-based spectroscopy, pump-probe experiments, and compressive sensing should benefit from coherent control of the comb-pulse time and phase.
51. X. Zhang, K. Beloy, Y. S. Hassan, W. F. McGrew, C-C Chen, J. L. Siegel, T. Grogan, A. D. Ludlow, "Sub-recoil clock-transition laser cooling enabling shallow optical lattice clocks", arXiv:2206.09056, DOI: 10.48550/arXiv.2206.09056
Laser cooling is a key ingredient for quantum control of atomic systems in a variety of settings. In divalent atoms, two-stage Doppler cooling is typically used to bring atoms to the uK regime. Here, we implement a pulsed radial cooling scheme using the ultranarrow 1S0-3P0 clock transition in ytterbium to realize sub-recoil temperatures, down to tens of nK. Together with sideband cooling along the one-dimensional lattice axis, we efficiently prepare atoms in shallow lattices at an energy of 6 lattice recoils. Under these conditions key limits on lattice clock accuracy and instability are reduced, opening the door to dramatic improvements. Furthermore, tunneling shifts in the shallow lattice do not compromise clock accuracy at the 10-19 level.
52. P.-Y. Hou, J. J. Wu, S. D. Erickson, D. C. Cole, G. Zarantonello, A. D. Brandt, A. C. Wilson, D. H. Slichter, D. Leibfried, "Coherently Coupled Mechanical Oscillators in the Quantum Regime", arXiv:2205.14841, DOI: 10.48550/arXiv.2205.14841
Coupled harmonic oscillators are ubiquitous in physics and play a prominent role in quantum science. They are a cornerstone of quantum mechanics and quantum field theory, where second quantization relies on harmonic oscillator operators to create and annihilate particles. Descriptions of quantum tunneling, beamsplitters, coupled potential wells, "hopping terms", decoherence and many other phenomena rely on coupled harmonic oscillators. Despite their prominence, only a few experimental systems have demonstrated direct coupling between separate harmonic oscillators; these demonstrations lacked the capability for high-fidelity quantum control. Here, we realize coherent exchange of single motional quanta between harmonic oscillators -- in this case, spectrally separated harmonic modes of motion of a trapped ion crystal where the timing, strength, and phase of the coupling are controlled through the application of an oscillating electric field with suitable spatial variation. We demonstrate high-fidelity quantum state transfer, entanglement of motional modes, and Hong-Ou-Mandel-type interference. We also project a harmonic oscillator into its ground state by measurement and preserve that state during repetitions of the projective measurement, an important prerequisite for non-destructive syndrome measurement in continuous-variable quantum error correction. Controllable coupling between harmonic oscillators has potential applications in quantum information processing with continuous variables, quantum simulation, and precision measurements. It can also enable cooling and quantum logic spectroscopy involving motional modes of trapped ions that are not directly accessible.
53. N. Hoghooghi, S. Xing, P. Chang, D. Lesko, A. Lind, G. Rieker, S. Diddams, "1-GHz mid-infrared frequency comb spanning 3 to 13 μm", arXiv:2201.07134, DOI: 10.48550/arXiv.2201.07134
Mid-infrared (MIR) spectrometers are invaluable tools for molecular fingerprinting and hyper-spectral imaging. Among the available spectroscopic approaches, GHz MIR dual-comb absorption spectrometers have the potential to simultaneously combine the high-speed, high spectral resolution, and broad optical bandwidth needed to accurately study complex, transient events in chemistry, combustion, and microscopy. However, such a spectrometer has not yet been demonstrated due to the lack of GHz MIR frequency combs with broad and full spectral coverage. Here, we introduce the first broadband MIR frequency comb laser platform at 1 GHz repetition rate that achieves spectral coverage from 3 to 13 {\mu}m. This frequency comb is based on a commercially available 1.56 {\mu}m mode-locked laser, robust all-fiber Er amplifiers and intra-pulse difference frequency generation (IP-DFG) of few-cycle pulses in \c{hi}(2) nonlinear crystals. When used in a dual comb spectroscopy (DCS) configuration, this source will simultaneously enable measurements with {\mu}s time resolution, 1 GHz (0.03 cm-1) spectral point spacing and a full bandwidth of >5 THz (>166 cm-1) anywhere within the MIR atmospheric windows. This represents a unique spectroscopic resource for characterizing fast and non-repetitive events that are currently inaccessible with other sources.
54. A. Mitra, S. Omanakuttan, M. J. Martin, G. W. Biedermann, I. H. Deutsch, "Practical and fundamental limits of neutral atom entanglement using Rydberg dressing", arXiv:2205.12866, DOI: 10.48550/arXiv.2205.12866
We revisit the implementation of a two-qubit entangling gate, the Mølmer-Sørensen gate, using the adiabatic Rydberg dressing paradigm. We study the implementation of rapid adiabatic passage using a two-photon transition, which does not require the use of an ultra-violet laser, and can be implemented using only amplitude modulation of one field with all laser frequencies fixed. We find that entangling gate fidelities, comparable to the one-photon excitation, are achievable with the two-photon excitation. Moreover, we address how the adiabatic dressing protocol can be used to implement entangling gates outside the regime of a perfect Rydberg blockade. We show that using adiabatic dressing we can achieve a scaling of gate fidelity set by the fundamental limits to entanglement generated by the Rydberg interactions while simultaneously retaining limited population in the doubly excited Rydberg state. This allows for fast high fidelity gates for atoms separated beyond the blockade radius.
55. R. A. Bravo, K. Najafi, X. Gao, S. F. Yelin, "Quantum reservoir computing using arrays of Rydberg atoms", arXiv:2111.10956, DOI: 10.48550/arXiv.2111.10956
Quantum computing promises to provide machine learning with computational advantages. However, noisy intermediate-scale quantum (NISQ) devices pose engineering challenges to realizing quantum machine learning (QML) advantages. Recently, a series of QML computational models inspired by the noise-tolerant dynamics on the brain have emerged as a means to circumvent the hardware limitations of NISQ devices. In this article, we introduce a quantum version of a recurrent neural network (RNN), a well-known model for neural circuits in the brain. Our quantum RNN (qRNN) makes use of the natural Hamiltonian dynamics of an ensemble of interacting spin-1/2 particles as a means for computation. In the limit where the Hamiltonian is diagonal, the qRNN recovers the dynamics of the classical version. Beyond this limit, we observe that the quantum dynamics of the qRNN provide it quantum computational features that can aid it in computation. To this end, we study a qRNN based on arrays of Rydberg atoms, and show that the qRNN is indeed capable of replicating the learning of several cognitive tasks such as multitasking, decision making, and long-term memory by taking advantage of several key features of this platform such as interatomic species interactions, and quantum many-body scars.
56. S. Ostermann, V. Walther, and S. F. Yelin, "Superglass formation in an atomic BEC with competing long-range interactions", Phys. Rev. Research 4, 023074 (2022), DOI: 10.1103/PhysRevResearch.4.023074
The complex dynamical phases of quantum systems are dictated by atomic interactions that usually evoke an emergent periodic order. Here, we study a quantum many-body system with two competing and substantially different long-range interaction potentials where the dynamical instability towards density order can give way to a disordered amorphous solid, which exhibits local density modulations but no long-range periodic order. We consider a two-dimensional Bose-Einstein condensate in the Rydberg-dressing regime coupled to an optical standing wave resonator. The dynamic pattern formation in this system is governed by the competition between the two involved interaction potentials: repulsive soft-core interactions arising due to Rydberg dressing and infinite-range sign changing interactions induced by the cavity photons. The amorphous phase is found when the two interaction potentials introduce incommensurate length scales. The dynamic formation of this peculiar phase can be attributed to frustration induced by the two competing interaction energies and length scales.
57. T. L. Patti, J. Kossaifi, A. Anandkumar, S. F. Yelin, "Quantum Semidefinite Programming with the Hadamard Test and Approximate Amplitude Constraints", arXiv:2206.14999, DOI: 10.48550/arXiv.2206.14999
Semidefinite programs are optimization methods with a wide array of applications, such as approximating difficult combinatorial problems. We introduce a variational quantum algorithm for semidefinite programs that uses only n qubits, a constant number of circuit preparations, and ${O(n^{2})}$ expectation values in order to solve semidefinite programs with up to ${N=2^{n}}$ variables and ${M=2^{n}}$ constraints. Efficient optimization is achieved by encoding the objective matrix as a properly parameterized unitary conditioned on an auxilary qubit, a technique known as the Hadamard Test. The Hadamard Test enables us to optimize the objective function by estimating only a single expectation value of the ancilla qubit, rather than separately estimating exponentially many expectation values. Similarly, we illustrate that the semidefinite programming constraints can be effectively enforced by implementing a second Hadamard Test, as well as imposing ${\sim \frac{n^{2}}{2}}$ Pauli string amplitude constraints. We demonstrate the effectiveness of our protocol by devising an efficient quantum implementation of the Goemans-Williamson algorithm, which is a useful approximation for various NP-hard problems, such as MaxCut. Our method exceeds the performance of analogous classical methods on a diverse subset of well-studied MaxCut problems from the GSet library.
58. J. Z. Lu, R. A. Bravo, K. Hou, G. A. Dagnew, S. F. Yelin, K. Najafi, "Learning quantum symmetries with interactive quantum-classical variational algorithms", arXiv:2206.11970, https://doi.org/10.48550/arXiv.2206.11970
A symmetry of a state  is a unitary operator of which $| \Psi\rangle$ is an eigenvector. When |ψ⟩ is an unknown state supplied by a black-box oracle, the state's symmetries serve to characterize it, and often relegate much of the desired information about $| \Psi\rangle$. In this paper, we develop a variational hybrid quantum-classical learning scheme to systematically probe for symmetries of $| \Psi\rangle$ with no a priori assumptions about the state. This procedure can be used to learn various symmetries at the same time. In order to avoid re-learning already known symmetries, we introduce an interactive protocol with a classical deep neural net. The classical net thereby regularizes against repetitive findings and allows our algorithm to terminate empirically with all possible symmetries found. Our scheme can be implemented efficiently on average with non-local SWAP gates; we also give a less efficient algorithm with only local operations, which may be more appropriate for current noisy quantum devices. We demonstrate our algorithm on representative families of states.
59. B. Wu, G. P. Greve, C. Luo, J. K. Thompson, “Site-dependent selection of atoms for homogeneous atom-cavity coupling,” arXiv:2104.01201 submitted to PRA, DOI: 10.48550/arXiv.2104.01201
We demonstrate a method to obtain homogeneous atom-cavity coupling by selecting and keeping 87Rb atoms that are near maximally coupled to the cavity's standing-wave mode. We select atoms by imposing an AC Stark shift on the ground state hyperfine microwave transition frequency with light injected into the cavity. We then induce a spin flip with microwaves that are resonant for atoms that are near maximally coupled to the cavity mode of interest, after which, we use radiation pressure forces to remove from the cavity all the atoms in the initial spin state. Achieving greater homogeneity in the atom-cavity coupling will potentially enhance entanglement generation, intracavity driving of atomic transitions, cavity-optomechanics, and quantum simulations. This approach can easily be extended to other atomic species with microwave or optical transitions.
60. G P. Greve, C. Luo, B. Wu, J. K. Thompson, “Entanglement-Enhanced Matter-Wave Interferometry in a High-Finesse Cavity”, arXiv:2110.14027, DOI:
10.48550/arXiv.2110.14027
Entanglement is a fundamental resource that allows quantum sensors to surpass the standard quantum limit set by the quantum collapse of independent atoms. Collective cavity-QED systems have succeeded in generating large amounts of directly observed entanglement involving the internal degrees of freedom of laser-cooled atomic ensembles. Here we demonstrate cavity-QED entanglement of external degrees of freedom to realize a matter-wave interferometer of 700 atoms in which each individual atom falls freely under gravity and simultaneously traverses two paths through space while also entangled with the other atoms. We demonstrate both quantum non-demolition measurements and cavity-mediated spin interactions for generating squeezed momentum states with directly observed metrological gain 3.4+1.1−0.9 dB and 2.5+0.6−0.6 dB below the standard quantum limit respectively. An entangled state is for the first time successfully injected into a Mach-Zehnder light-pulse interferometer with 1.7+0.5−0.5 dB of directly observed metrological enhancement. Reducing the fundamental quantum source of imprecision provides a new resource that can be exploited to directly enhance measurement precision, bandwidth, and accuracy or operate at reduced size. These results also open a new path for combining particle delocalization and entanglement for inertial sensors, searches for new physics, particles, and fields, future advanced gravitational wave detectors, and accessing beyond mean-field quantum many-body physics.
61. S. P. Kelly, J. K Thompson, A. M. Rey, J. Marino, “Resonant light enhances phase coherence in a cavity QED simulator of fermionic superfluidity”, arXiv preprint arXiv:2202.05851, DOI: 10.48550/arXiv.2202.05851
Cavity QED experiments are natural hosts for non-equilibrium phases of matter supported by photon-mediated interactions. In this work, we consider a cavity QED simulation of the BCS model of superfluidity, by studying regimes where the cavity photons act as dynamical degrees of freedom instead of mere mediators of the interaction via virtual processes. We find an enhancement of long time coherence following a quench whenever the cavity frequency is tuned into resonance with the atoms. We discuss how this is equivalent to enhancement of non-equilibrium superfluidity and highlight similarities to an analogous phenomena recently studied in solid state quantum optics. We also discuss the conditions for observing this enhanced resonant pairing in experiments by including the effect of photon losses and inhomogeneous coupling in our analysis.
62. J. P. Bartolotta, S. B. Jäger, J. T. Reilly, M. A. Norcia, J. K. Thompson, G. Smith, M. J. Holland, “Entropy transfer from a quantum particle to a classical coherent light field”, Phys. Rev. Res. 4 013218, DOI: 10.1103/PhysRevResearch.4.013218
In the field of light-matter interactions, it is often assumed that a classical light field that interacts with a quantum particle remains almost unchanged and thus contains nearly no information about the manipulated particles. To investigate the validity of this assumption, we develop and theoretically analyze a simple Gedanken experiment, which involves the interaction of a coherent state with a quantum particle in an optical cavity. We quantify the resulting alteration of the light field by calculating the fidelity of its initial and equilibrium states. Using Bayesian inference, we demonstrate the information transfer through photon statistics. In addition, we employ the concepts of quantum entropy and mutual information to quantify the entropy transfer from the particle to the light field. In the weak coupling limit, we validate the usually assumed negligible alteration of the light field and entropy transfer. In the strong coupling limit, however, we observe that the information of the initial particle state can be fully encoded in the light field, even for large photon numbers. Nevertheless, we show that spontaneous emission is a sufficient mechanism for removing the entropy initially stored in the particle. Our analysis provides a deeper understanding of the entropy exchange between quantum matter and classical light.
63. T. Wilkason, M. Nantel, J. Rudolph, Y. Jiang, B. E. Garber, H. Swan, S. P. Carman, M. Abe, J. M. Hogan, "Atom Interferometry with Floquet Atom Optics", arXiv.2205.06965, DOI: 10.48550/arXiv.2205.06965
Floquet engineering offers a compelling approach for designing the time evolution of periodically driven systems. We implement a periodic atom-light coupling to realize Floquet atom optics on the strontium $^{1}S_{0} - ^{3}P_{1}$ transition. These atom optics reach pulse efficiencies above 99.4\% over a wide range of frequency offsets between light and atomic resonance, even under strong driving where this detuning is on the order of the Rabi frequency. Moreover, we use Floquet atom optics to compensate for differential Doppler shifts in large momentum transfer atom interferometers and achieve state-of-the-art momentum separation in excess of 400 $\hbar k$. This technique can be applied to any two-level system at arbitrary coupling strength, with broad application in coherent quantum control.
64. S. Buckley-Bonanno, S. Ostermann, O. Rubies-Bigorda, T. L. Patti, S. F. Yelin, "Optimized geometries for cooperative photon storage in an impurity coupled to a two-dimensional atomic array", arXiv:2207.02908, DOI: https://doi.org/10.48550/arXiv.2207.02908
The collective modes of two-dimensional ordered atomic arrays can modify the radiative environment of embedded atomic impurities. We analyze the role of the lattice geometry on the impurity's emission linewidth by comparing the effective impurity decay rate obtained for all non-centered Bravais lattices and an additional honeycomb lattice. We demonstrate that the lattice geometry plays a crucial role in determining the effective decay rate for the impurity. In particular, we find that the minimal effective decay rate appears in lattices where the number of the impurity's nearest neighbours is maximal and the number of distinct distances among nearest neighbours is minimal. We further show that, in the choice between interstitial and substitutional placement of the impurity, the former always wins by exhibiting a lower decay rate and longer photon storage. For interstitial placements, we determine the optimal impurity position in the lattice plane, which is not necessarily found in the center of the lattice plaquette.
65. W. Zhong, X. Gao, S. F. Yelin, K. Najafi, "Many-body localized hidden Born machine", arXiv:2207.02346, 10.48550/arXiv.2207.02346
Born Machines are quantum-inspired generative models that leverage the probabilistic nature of quantum states. Here, we present a new architecture called many-body localized (MBL) hidden Born machine that uses both MBL dynamics and hidden units as learning resources. We theoretically prove that MBL Born machines possess more expressive power than classical models, and the introduction of hidden units boosts its learning power. We numerically demonstrate that the MBL hidden Born machine is capable of learning a toy dataset consisting of patterns of MNIST handwritten digits, quantum data obtained from quantum many-body states, and non-local parity data. In order to understand the mechanism behind learning, we track physical quantities such as von Neumann entanglement entropy and Hamming distance during learning, and compare the learning outcomes in the MBL, thermal, and Anderson localized phases. We show that the superior learning power of the MBL phase relies importantly on both localization and interaction. Our architecture and algorithm provide novel strategies of utilizing quantum many-body systems as learning resources, and reveal a powerful connection between disorder, interaction, and learning in quantum systems.
66. J. T. Reilly, S. B. Jäger, J. Cooper, M. J. Holland, "Adiabatic Control of Decoherence-Free-Subspaces in an Open Collective System", to be published Phys. Rev. A (2022), available as arXiv preprint arXiv:2201.12379, DOI: 10.48550/arXiv.2201.12379
We propose a method to adiabatically control an atomic ensemble using a decoherence-free subspace (DFS) within a dissipative cavity. We can engineer a specific eigenstate of the system's Lindblad jump operators by injecting a field into the cavity which deconstructively interferes with the emission amplitude of the ensemble. In contrast to previous adiabatic DFS proposals, our scheme creates a DFS in the presence of collective decoherence. We therefore have the ability to engineer states that have high multi-particle entanglements which may be exploited for quantum information science or metrology. We further demonstrate a more optimized driving scheme that utilizes the knowledge of possible diabatic evolution gained from the so-called adiabatic criteria. This allows us to evolve to a desired state with exceptionally high fidelity on a time scale that does not depend on the number of atoms in the ensemble. By engineering the DFS eigenstate adiabatically, our method allows for faster state preparation than previous schemes that rely on damping into a desired state solely using dissipation.
67. S. B. Jäger, T. Schmit, G. Morigi, M. J. Holland, R. Betzholz, "Lindblad master equations for quantum systems coupled to dissipative bosonic modes", arXiv:2203.03302, DOI: 10.48550/arXiv.2203.03302
We present a general approach to derive Lindblad master equations for a subsystem whose dynamics is coupled to dissipative bosonic modes. The derivation relies on a Schrieffer-Wolff transformation which allows to eliminate the bosonic degrees of freedom after self-consistently determining their state as a function of the coupled quantum system. We apply this formalism to the dissipative Dicke model and derive a Lindblad master equation for the atomic spins, which includes the coherent and dissipative interactions mediated by the bosonic mode. This master equation accurately predicts the Dicke phase transition and gives the correct steady state. In addition, we compare the dynamics using exact diagonalization and numerical integration of the master equation with the predictions of semiclassical trajectories. We finally test the performance of our formalism by studying the relaxation of a NOON state and show that the dynamics captures quantum metastability beyond the mean-field approximation.
68. J. D. Wilson, S. B. Jäger, J. T. Reilly, A. Shankar, M.L. Chiofalo, M. J. Holland, "Beyond one-axis twisting: Simultaneous spin-momentum squeezing", submitted to Phys. Rev. A (2022); arXiv:2206.12491, DOI: 10.48550/arXiv.2206.12491
The creation and manipulation of quantum entanglement is central to improving precision measurements. A principal method of generating entanglement for use in atom interferometry is the process of spin squeezing whereupon the states become more sensitive to SU(2) rotations. One possibility to generate this entanglement is provided by one-axis twisting (OAT), where a many-particle entangled state of one degree of freedom is generated by a non-linear Hamiltonian. We introduce a novel method which goes beyond OAT to create squeezing and entanglement across two distinct degrees of freedom. We present our work in the specific physical context of a system consisting of collective atomic energy levels and discrete collective momentum states, but also consider other possible realizations. Our system uses a nonlinear Hamiltonian to generate dynamics in SU(4), thereby creating the opportunity for dynamics not possible in typical SU(2) one-axis twisting. This leads to three axes undergoing twisting due to the two degrees of freedom and their entanglement, with the resulting potential for a more rich context of quantum entanglement. The states prepared in this system are potentially more versatile for use in multi-parameter or auxiliary measurement schemes than those prepared by standard spin squeezing.
69. G. W. Harmon, J. T. Reilly, M. J. Holland, S. B. Jäger, "Mean-field Floquet theory for a three-level cold-atom laser", Phys. Rev. A 106, 013706 (2022), DOI: 10.1103/PhysRevA.106.013706
We present a theoretical description for a lasing scheme for atoms with three internal levels in a V configuration and interacting with an optical cavity. The use of a V-level system allows for an efficient closed lasing cycle to be sustained on a dipole-forbidden transition without the need for incoherent repumping. This is made possible by utilizing an additional dipole-allowed transition. We determine the lasing threshold and emission frequency by performing a stability analysis of the nonlasing solution. In the lasing regime, we use a mean-field Floquet method (MFFM) to calculate the lasing intensity and emission frequency. This MFFM predicts the lasing transition to be accompanied by the breaking of a continuous U(1) symmetry in a single Fourier component of the total field. In addition, we use the MFFM to derive bistable lasing and nonlasing solutions that highlight the nonlinear nature of this system. We then test the bistability by studying hysteresis when slowly ramping external parameters across the threshold and back. Furthermore, we also compare our mean-field results to a second-order cumulant approach. The work provides simple methods for understanding complex physics that occur in cold atom lasers with narrow line transitions.
70. N. Schine, A. W. Young, W. Eckner, M. Martin, A. M. Kaufman, "Long-Lived Bell states in an array of optical clock qubits", Nature Physics, in press(2022), arXiv:2111.14653, DOI: 10.48550/arXiv.2111.14653
The generation of long-lived entanglement on an optical clock transition is a key requirement to unlocking the promise of quantum metrology. Arrays of neutral atoms constitute a capable quantum platform for accessing such physics, where Rydberg-based interactions may generate entanglement between individually controlled and resolved atoms. To this end, we leverage the programmable state preparation afforded by optical tweezers along with the efficient strong confinement of a 3d optical lattice to prepare an ensemble of strontium atom pairs in their motional ground state. We engineer global single-qubit gates on the optical clock transition and two-qubit entangling gates via adiabatic Rydberg dressing, enabling the generation of Bell states, $| \Psi \rangle=\frac{1}{\sqrt{2}}(| gg \rangle + i| ee \rangle)$, with a fidelity of F =92.8(2.0)\%. For use in quantum metrology, it is furthermore critical that the resulting entanglement be long lived; we find that the coherence of the Bell state has a lifetime of $\tau_{bc}$ = 4.2(6) s via parity correlations and simultaneous comparisons between entangled and unentangled ensembles. Such Bell states can be useful for enhancing metrological stability and bandwidth. Further rearrangement of hundreds of atoms into arbitrary configurations using optical tweezers will enable implementation of many-qubit gates and cluster state generation, as well as explorations of the transverse field Ising model and Hubbard models with entangled or finite-range-interacting tunnellers.
71. S. Colombo, E. Pedrozo-Penafiel, A. Adiyatullin, Z. Li, E. Mendez, C. Shu, and V. Vuletić, "Time-reversal-based quantum metrology with many-body entangled states", Nature Phys. (2022); DOI: 10.1038/s41567-022-01653-5
Linear quantum measurements with independent particles are bounded by the standard quantum limit, which limits the precision achievable in estimating unknown phase parameters. The standard quantum limit can be overcome by entangling the particles, but the sensitivity is often limited by the final state readout, especially for complex entangled many-body states with non-Gaussian probability distributions. Here, by implementing an effective time-reversal protocol in an optically engineered many-body spin Hamiltonian, we demonstrate a quantum measurement with non-Gaussian states with performance beyond the limit of the readout scheme. This signal amplification through a time-reversed interaction achieves the greatest phase sensitivity improvement beyond the standard quantum limit demonstrated to date in any full Ramsey interferometer. These results open the field of robust time-reversal-based measurement protocols offering precision not too far from the Heisenberg limit. Potential applications include quantum sensors that operate at finite bandwidth, and the principle we demonstrate may also advance areas such as quantum engineering, quantum measurements and the search for new physics using optical-transition atomic clocks.

## Strongly Related Publications by Q-SEnSE Investigators

1. R. Srinivas, S. C. Burd, H. M. Knaack, R. T. Sutherland, A. Kwiatkowski, S. Glancy, E. Knill, D. J. Wineland, D. Leibfried, A. C. Wilson, D. T. C. Allcock, D. H. Slichter, "High-fidelity laser-free universal control of two trapped ion qubits", Nature 597, 209 (2021), DOI https://doi.org/10.1038/s41586-021-03809-4
2. A. W. Young, W. J. Eckner, W. R. Milner, D. Kedar, M. A. Norcia , E. Oelker , N. Schine , J. Ye & A. M. Kaufman, "Half-minute-scale atomic coherence and high relative stability in a tweezer clock", Nature, Vol 588, 17 December 2020
3. E. Pedrozo-Peñafiel, S. Colombo, C. Shu, A. F. Adiyatullin, Z. Li, E. Mendez, B.s Braverman, A. Kawasaki, D. Akamatsu, Y. Xiao and V. Vuletić, "Entanglement on an optical atomic-clock transition", Nature 588, 414–418, 16 December 2020, https://doi.org/10.1038/s41586-020-3006-1
4. J. Ye, N. Mavalvala, R. G. Beausoleil, P. M. Dehmer, L. L. Dimauro, M. Gaarde, S. Girvin, C. H. Greene, T. J. Ha, M. Kasevich, M. Lipson, M. D. Lukin, A. M. Lyyra, P. J. Reynolds, M. Safronova, and P. Zoller, "Manipulating Quantum Systems: An Assessment of Atomic, Molecular, and Optical Physics in the United States", http://nasedu/AMO2020 (2019) (2019). 10.17226/25613
5. S. C. Burd, R. Srinivas, J. J. Bollinger, A. C. Wilson, D. J. Wineland, D. Leibfried, D. H. Slichter, and D. T. C. Allcock, "Quantum amplification of mechanical oscillator motion", Science 364, 1163-1165 (2019). 10.1126/science.aaw2884
6. K. C. McCormick, J. Keller, S. C. Burd, D. J. Wineland, A. C. Wilson, and D. Leibfried, "Quantum-enhanced sensing of a single-ion mechanical oscillator", Nature 572, 86-90 (2019). 10.1038/s41586-019-1421-y
7. K. van Bibber, K. Lehnert, and A. Chou, "Putting the squeeze on axions", Phys Today 72, 48 (2019). 10.1063/PT.3.4227
8. J. Rudolph, T. Wilkason, M. Nantel, H. Swan, C. M. Holland, Y. Jiang, B. E. Garber, S. P. Carman, and J. M. Hogan, "Large Momentum Transfer Clock Atom Interferometry on the 689 nm Intercombination Line of Strontium", arXiv:191005459 (2019).
9. M. Mamaev, R. Blatt, J. Ye, and A. M. Rey, "Cluster State Generation with Spin-Orbit Coupled Fermionic Atoms in Optical Lattices", Phys Rev Lett 122, 160402 (2019). 10.1103/PhysRevLett.122.160402
10. J. M. Robinson, E. Oelker, W. R. Milner, W. Zhang, T. Legero, D. G. Matei, F. Riehle, U. Sterr, and J. Ye, "Crystalline optical cavity at 4 K with thermal-noise-limited instability and ultralow drift", Optica 6, 240-243 (2019). 10.1364/optica.6.000240
11. M. A. Norcia, A. W. Young, W. J. Eckner, E. Oelker, J. Ye, and A. M. Kaufman, "Seconds-scale coherence in a tweezer-array optical clock", Science 366, 93-97 (2019). 10.1126/science.aay0644
12. E. Oelker, R. B. Hutson, C. J. Kennedy, L. Sonderhouse, T. Bothwell, A. Goban, D. Kedar, C. Sanner, J. M. Robinson, G. E. Marti, D. G. Matei, T. Legero, M. Giunta, R. Holzwarth, F. Riehle, U. Sterr, and J. Ye, "Demonstration of 4.8 × 10−17 stability at 1 s for two independent optical clocks", Nat Photonics 13, 714-719 (2019). 10.1038/s41566-019-0493-4
13. D. Barberena, R. J. Lewis-Swan, J. K. Thompson, and A. M. Rey, "Driven-dissipative quantum dynamics in ultra-long-lived dipoles in an optical cavity", Phys Rev A 99, 053411 (2019). 10.1103/PhysRevA.99.053411
14. L. Anderegg, L. W. Cheuk, Y. Bao, S. Burchesky, W. Ketterle, K.-K. Ni, and J. M. Doyle, "An Optical Tweezer Array of Ultracold Molecules", Science 365, 1156-1158 (2019). 10.1126/science.aax1265
15. A. D. Draper, R. K. Cole, A. S. Makowiecki, J. Mohr, A. Zdanowicz, A. Marchese, N. Hoghooghi, and G. B. Rieker, "Broadband dual-frequency comb spectroscopy in a rapid compression machine", Opt Express 27, 10814-10825 (2019). 10.1364/oe.27.010814
16. C. B. Alden, S. C. Coburn, R. J. Wright, E. Baumann, K. Cossel, E. Perez, E. Hoenig, K. Prasad, I. Coddington, and G. B. Rieker, "Single-Blind Quantification of Natural Gas Leaks from 1 km Distance Using Frequency Combs", Envir Sci Tech Lib 53, 2908-2917 (2019). 10.1021/acs.est.8b06259
17. L. Ríos, B. Pollard, D. R. Dounas-Frazer, and H. J. Lewandowski, "Using think-aloud interviews to characterize model-based reasoning in electronics for a laboratory course assessment", Phys Rev Phys Educ Res 15, 010140 (2019). 10.1103/PhysRevPhysEducRes.15.010140
18. M. Malnou, D. A. Palken, B. M. Brubaker, L. R. Vale, G. C. Hilton, and K. W. Lehnert, "Squeezed Vacuum Used to Accelerate the Search for a Weak Classical Signal", Phys Rev X 9, 021023 (2019). 10.1103/PhysRevX.9.021023
19. S. M. Brewer, J.-S. Chen, A. M. Hankin, E. R. Clements, C. W. Chou, D. J. Wineland, D. B. Hume, and D. R. Leibrandt, "An 27 Al + quantum-logic clock with systematic uncertainty below 10−18", Phys Rev Lett 123, 033201 (2019). 10.1103/PhysRevLett.123.033201
20. H. Bergeron, L. C. Sinclair, W. C. Swann, I. Khader, K. C. Cossel, M. Cermak, J. D. Deschenes, and N. R. Newbury, "Femtosecond time synchronization of optical clocks off of a flying quadcopter", Nat Commun 10, 7 (2019). 10.1038/s41467-019-09768-9
21. L. C. Sinclair, H. Bergeron, W. C. Swann, I. Khader, K. C. Cossel, M. Cermak, N. R. Newbury, and J. D. Deschenes, "Femtosecond optical two-way time-frequency transfer in the presence of motion", Phys Rev A 99, 023844 (2019). 10.1103/PhysRevA.99.023844
22. A. Shankar, L. Salvi, M. L. Chiofalo, N. Poli, and M. J. Holland, "Squeezed state metrology with Bragg interferometers operating in a cavity", Quantum Science and Technology 4, 045010 (2019). 10.1088/2058-9565/ab455d
23. A. Shankar, G. P. Greve, B. Wu, J. K. Thompson, and M. Holland, "Continuous Real-Time Tracking of a Quantum Phase Below the Standard Quantum Limit", Phys Rev Lett 122, 233602 (2019). 10.1103/PhysRevLett.122.233602
24. W. R. Milner, J. M. Robinson, C. J. Kennedy, T. Bothwell, D. Kedar, D. G. Matei, T. Legero, U. Sterr, F. Riehle, H. Leopardi, T. M. Fortier, J. A. Sherman, J. Levine, J. Yao, J. Ye, and E. Oelker, "Demonstration of a Timescale Based on a Stable Optical Carrier", Phys Rev Lett 123, 173201 (2019). 10.1103/PhysRevLett.123.173201
25. R. B. Hutson, A. Goban, G. E. Marti, L. Sonderhouse, C. Sanner, and J. Ye, "Engineering Quantum States of Matter for Atomic Clocks in Shallow Optical Lattices", Phys Rev Lett 123, 123401 (2019). 10.1103/PhysRevLett.123.123401
26. P. He, M. A. Perlin, S. R. Muleady, R. J. Lewis-Swan, R. B. Hutson, J. Ye, and A. M. Rey, "Engineering spin squeezing in a 3D optical lattice with interacting spin-orbit-coupled fermions", Physical Review Research 1, 033075 (2019). 10.1103/PhysRevResearch.1.033075
27. A. Piñeiro Orioli and A. M. Rey, "Dark states of multilevel fermionic atoms in doubly-filled optical lattices", Phys Rev Lett 123, 223601 (2019). 10.1103/PhysRevLett.123.223601
28. C. Qu and A. M. Rey, "Spin squeezing and many-body dipolar dynamics in optical lattice clocks", Phys Rev A 100, 041602 (2019). 10.1103/PhysRevA.100.041602
29. M. S. Safronova, D. Budker, D. DeMille, D. F. J. Kimball, A. Derevianko, and C. W. Clark, "Search for new physics with atoms and molecules", Rev Mod Phys 90, 025008 (2018). 10.1103/RevModPhys.90.025008
30. M. A. Norcia, A. W. Young, and A. M. Kaufman, "Microscopic Control and Detection of Ultracold Strontium in Optical-Tweezer Arrays", Phys Rev X 8, 041054 (2018). 10.1103/PhysRevX.8.041054
31. A. Goban, R. B. Hutson, G. E. Marti, S. L. Campbell, M. A. Perlin, P. S. Julienne, J. P. D’Incao, A. M. Rey, and J. Ye, "Emergence of multi-body interactions in a fermionic lattice clock", Nature 563, 369-373 (2018). 10.1038/s41586-018-0661-6
32. I. Kozyryev, Z. Lasner, and J. M. Doyle, "Enhanced Sensitivity to Ultralight Bosonic Dark Matter in the Spectra of the Linear Radical SrOH", arXiv:180508185 (2018).
33. I. Kozyryev, L. Baum, L. Aldridge, P. Yu, E. E. Eyler, and J. M. Doyle, "Coherent Bichromatic Force Deflection of Molecules", Phys Rev Lett 120, 063205 (2018). 10.1103/PhysRevLett.120.063205
34. T. Thiele, Y. Lin, M. O. Brown, and C. A. Regal, "Self-Calibrating Vector Atomic Magnetometry through Microwave Polarization Reconstruction", Phys Rev Lett 121, 153202 (2018). 10.1103/PhysRevLett.121.153202
35. C. A. Weidner and D. Z. Anderson, "Simplified landscapes for optimization of shaken lattice interferometry", New J Phys 20, 075007 (2018). 10.1088/1367-2630/aad36c
36. C. A. Weidner and D. Z. Anderson, "Experimental Demonstration of Shaken-Lattice Interferometry", Phys Rev Lett 120, 263201 (2018). 10.1103/PhysRevLett.120.263201
37. M. A. Norcia, J. R. K. Cline, J. A. Muniz, J. M. Robinson, R. B. Hutson, A. Goban, G. E. Marti, J. Ye, and J. K. Thompson, "Frequency Measurements of Superradiance from the Strontium Clock Transition", Phys Rev X 8, 021036 (2018). 10.1103/PhysRevX.8.021036
38. P. Wcisło, P. Ablewski, K. Beloy, S. Bilicki, M. Bober, R. Brown, R. Fasano, R. Ciuryło, H. Hachisu, T. Ido, J. Lodewyck, A. Ludlow, W. McGrew, P. Morzyński, D. Nicolodi, M. Schioppo, M. Sekido, R. Le Targat, P. Wolf, X. Zhang, B. Zjawin, and M. Zawada, "New bounds on dark matter coupling from a global network of optical atomic clocks", Science Advances 4, eaau4869 (2018). 10.1126/sciadv.aau4869
39. M. A. Norcia, R. J. Lewis-Swan, J. R. K. Cline, B. Zhu, A. M. Rey, and J. K. Thompson, "Cavity-mediated collective spin-exchange interactions in a strontium superradiant laser", Science 361, 259-262 (2018). 10.1126/science.aar3102
40. J. P. Bartolotta, M. A. Norcia, J. R. K. Cline, J. K. Thompson, and M. J. Holland, "Laser cooling by sawtooth-wave adiabatic passage", Phys Rev A 98, 023404 (2018). 10.1103/PhysRevA.98.023404
41. M. A. Norcia, J. R. K. Cline, J. P. Bartolotta, M. J. Holland, and J. K. Thompson, "Narrow-line laser cooling by adiabatic transfer", New J Phys 20, 023021 (2018). 10.1088/1367-2630/aaa950
42. Q.-Y. Liang, A. V. Venkatramani, S. H. Cantu, T. L. Nicholson, M. J. Gullans, A. V. Gorshkov, J. D. Thompson, C. Chin, M. D. Lukin, and V. Vuletić, "Observation of three-photon bound states in a quantum nonlinear medium", Science 359, 783-786 (2018). 10.1126/science.aao7293
43. D. S. Wild, E. Shahmoon, S. F. Yelin, and M. D. Lukin, "Quantum Nonlinear Optics in Atomically Thin Materials", Phys Rev Lett 121, 123606 (2018). 10.1103/PhysRevLett.121.123606
44. M. G. Kozlov, M. S. Safronova, J. R. Crespo López-Urrutia, and P. O. Schmidt, "Highly charged ions: Optical clocks and applications in fundamental physics", Rev Mod Phys 90, 045005 (2018). 10.1103/RevModPhys.90.045005
45. S. G. Porsev, M. S. Safronova, U. I. Safronova, and M. G. Kozlov, "Multipolar Polarizabilities and Hyperpolarizabilities in the Sr Optical Lattice Clock", Phys Rev Lett 120, 063204 (2018). 10.1103/PhysRevLett.120.063204
46. X. D. Qi, Y. Y. Jau, and I. H. Deutsch, "Enhanced cooperativity for quantum-nondemolition-measurement-induced spin squeezing of atoms coupled to a nanophotonic waveguide", Phys Rev A 97, 11 (2018). 10.1103/PhysRevA.97.033829
47. S. Coburn, C. B. Alden, R. Wright, K. Cossel, E. Baumann, G.-W. Truong, F. Giorgetta, C. Sweeney, N. R. Newbury, K. Prasad, I. Coddington, and G. B. Rieker, "Regional trace-gas source attribution using a field-deployed dual frequency comb spectrometer", Optica 5, 320-327 (2018). 10.1364/optica.5.000320
48. D. R. Dounas-Frazer, L. Ríos, B. Pollard, J. T. Stanley, and H. J. Lewandowski, "Characterizing lab instructors' self-reported learning goals to inform development of an experimental modeling skills assessment", Phys Rev Phys Educ Res 14, 020118 (2018). 10.1103/PhysRevPhysEducRes.14.020118
49. L. Zhong, S. Al Kenany, K. M. Backes, B. M. Brubaker, S. B. Cahn, G. Carosi, Y. V. Gurevich, W. F. Kindel, S. K. Lamoreaux, K. W. Lehnert, S. M. Lewis, M. Malnou, R. H. Maruyama, D. A. Palken, N. M. Rapidis, J. R. Root, M. Simanovskaia, T. M. Shokair, D. H. Speller, I. Urdinaran, and K. A. van Bibber, "Results from phase 1 of the HAYSTAC microwave cavity axion experiment", Phys Rev D 97, 092001 (2018). 10.1103/PhysRevD.97.092001
50. G. E. Marti, R. B. Hutson, A. Goban, S. L. Campbell, N. Poli, and J. Ye, "Imaging Optical Frequencies with 100 mHz Precision and 1.1 mm Resolution", Phys Rev Lett 120, 103201 (2018). 10.1103/PhysRevLett.120.103201
51. W. F. McGrew, X. Zhang, R. J. Fasano, S. A. Schäffer, K. Beloy, D. Nicolodi, R. C. Brown, N. Hinkley, G. Milani, M. Schioppo, T. H. Yoon, and A. D. Ludlow, "Atomic clock performance enabling geodesy below the centimetre level", Nature 564, 87-90 (2018). 10.1038/s41586-018-0738-2
52. R. J. Lewis-Swan, M. A. Norcia, J. R. K. Cline, J. K. Thompson, and A. M. Rey, "Robust Spin Squeezing via Photon-Mediated Interactions on an Optical Clock Transition", Phys Rev Lett 121, 070403 (2018). 10.1103/PhysRevLett.121.070403
53. S. L. Bromley, S. Kolkowitz, T. Bothwell, D. Kedar, A. Safavi-Naini, M. L. Wall, C. Salomon, A. M. Rey, and J. Ye, "Dynamics of interacting fermions under spin–orbit coupling in an optical lattice clock", Nat Phys 14, 399-404 (2018). 10.1038/s41567-017-0029-0