Bulletin of the American Physical Society
50th Annual Meeting of the APS Division of Atomic, Molecular and Optical Physics APS Meeting
Volume 64, Number 4
Monday–Friday, May 27–31, 2019; Milwaukee, Wisconsin
Session P04: Open Quantum Systems |
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Chair: Dominik Schneble, Stony Brook University Room: Wisconsin Center 102AB |
Thursday, May 30, 2019 10:30AM - 10:42AM |
P04.00001: Thermalization in the Quantum Ising Model -- Approximations, Limits, and Beyond Lincoln D. Carr, Daniel Jaschke, Ines de Vega We present quantitative predictions for quantum simulator experiments on Ising models from trapped ions to Rydberg chains and show how the environment can be used to control thermalization and thus decoherence times with global, local, and endcap reservoirs. We find (i) local reservoirs enable more rapid thermalization in comparison to a global one; (ii) the thermalization timescale depends strongly on the position in the Ising phase diagram; and (iii) for a global reservoir larger system sizes show a significant slow down in the thermalization process. We find it is necessary to treat the full multi-channel Lindblad master equation rather than the commonly used single-channel local Lindblad approximation to make accurate predictions on a classical computer. This reduces the number of qubits one can practically classical simulate by a factor of 4, in turn showing quantum advantage at a factor of 4 smaller qubit number for open quantum systems as opposed to closed ones. Thus our results encourage open quantum system exploration in noisy intermediate-scale quantum (NISQ) technologies. [Preview Abstract] |
Thursday, May 30, 2019 10:42AM - 10:54AM |
P04.00002: A heralded quantum memory scheme with high storage-retrieve efficiency Zhiqiang Zhang, Ravi Kumar, Mathias Alexander Seidler, Chern Hui Lee, Kyle Arnold, Murray Barrett The faithful storage and retrieval of a quantum bit of light is of fundamental importance for quantum communication, quantum networking and quantum computation. Here, we demonstrate a heralded quantum memory scheme in an atomic optical cavity system with both high storage and retrieval efficiency. A 3\% total storage-retrieval efficiency is reached by using a coherent pulse, which is around 10000 times higher than experiment previously presented \footnote{Tanji, H. and Ghosh, Phys. Rev. Lett. \textbf{103}, 043601 (2009)}. Replacing the coherent pulse with a heralded single photon produced from four-wave mixing \footnote{B. Srivathsan and G. K. Gulati, Phys. Rev. Lett. \textbf{111},123602 (2013)}, we demonstrate a storage efficiency of 0.92\%. This is an important step towards realizing a high-efficiency heralded quantum memory for a single photon. [Preview Abstract] |
Thursday, May 30, 2019 10:54AM - 11:06AM |
P04.00003: Steady-State Superradiant Laser with an Atomic Beam Source Haonan Liu, John Cooper, Athreya Shankar, Murray Holland The steady-state superradiance of atoms that possess an ultranarrow linewidth transition has promised to serve as a coherent light source with a linewidth as narrow as millihertz. However, due to radiative heating caused by the incoherent pumping process, the required parameter regime can be difficult to realize in experiments. Here we propose a new configuration of the superradiance laser, a superradiant atomic beam laser, which uses a continuous beam of excited atoms as its energy source instead of in situ incoherent pumping. The fact that the Lamb-Dicke approximation is not valid in the atomic beam configuration requires us to study the system with transverse Doppler effects and consider the effects of atomic beam spread. Our numerical simulations show that in the limit of large atomic flux, it is possible to realize steady-state superradiance with an ultranarrow linewidth. A wide parameter range for the cavity to atomic decay rate ratio has been explored, covering the lasing regime to the bad-cavity superradiance regime. A simple analytical model is given and real experimental parameters are suggested. [Preview Abstract] |
Thursday, May 30, 2019 11:06AM - 11:18AM |
P04.00004: Open Dicke model: Unusual Dynamics of the Superradiant Transition Daniel Paz, Mohammad Maghrebi The interaction of an ensemble of two-level atoms with a single electromagnetic mode, the Dicke model, is a classic problem that exhibits a superradiant phase with a macroscopic population of photons. The transition to a superradiant phase has been recently observed in open driven systems that are subject to dissipation. It is widely believed that these phase transitions are effectively described by purely dissipative classical models with infinite-range interactions. While this is generally the case, I argue that the phase transition at weak dissipation displays qualitatively different dynamics that is not purely dissipative. Therefore, a dynamical crossover emerges as the dissipation is decreased. I also discuss the signatures of this unusual dynamics in available experimental setups. [Preview Abstract] |
Thursday, May 30, 2019 11:18AM - 11:30AM |
P04.00005: Berry curvature for non-interacting fermions at finite temperature Lukas Wawer, Michael Fleischhauer Recently, several attempts were made to generalize the concept of topology to finite-temperatures states of non-interacting fermions. While for one-dimensional systems generalizations of the geometric Berry phase to density matrices based on the Uhlmann construction can be used for this purpose, their application to higher dimensions is faced with difficulties [1]. We show that in contrast the Ensemble Geometric Phase (EGP) introduced in [2], which is based on the many-body polarization, allows one to define a proper Berry curvature for finite-temperature states of 2D lattice fermions. The corresponding Chern number for the mixed-state Berry curvature is shown to be identical to that of the gapped ground state. We illustrate our findings with numerical simulations of the Harper-Hofstadter and the Qi-Wu-Zhang model. \newline [1] J. C. Budich, and S. Diehl, Phys. Rev. B 91, 165140 (2915) \newline [2] C. E. Bardyn, L. Wawer, A. Altland, M. Fleischhauer, S. Diehl, PRX 8, 011035 (2018) [Preview Abstract] |
Thursday, May 30, 2019 11:30AM - 11:42AM |
P04.00006: Reservoir Engineering Enhanced Quantum State Preparation and Cooling Hil Fung Harry Cheung, Yogesh Patil, Mukund Vengalattore Feedback cooling and control using weak continuous measurement have traditionally been applied to quantum systems that are in contact with a Markovian reservoir (see for example, [1]). ~The realization of open quantum systems with artificially imposed non-Markovian dynamics offers a promising new route to robust techniques of quantum state preparation. In an optomechanical system of a silicon nitride membrane resonator with artificially engineered non-Markovian system-reservoir interactions, we experimentally demonstrate that feedback cooling can achieve over 300-fold lower final temperatures than obtained in the Markovian limit. ~Building on these substantial enhancements, we use optimal control theory to design system-reservoir interactions to implement enhanced and robust state preparation, and in particular, explore non-Markovian interactions for the generation of non-Gaussian quantum states in optomechanical systems [see also 2]. We further evaluate potential enhancements for force-sensing and metrological applications in the context of cavity optomechanical systems using such reservoir-engineered interactions. [1] A. C. Doherty and K. Jacobs, Phys. Rev. A 60, 2700 (1999) [2] S. Diehl et. al., Nature Physics 4, 878 - 883 (2008) [Preview Abstract] |
Thursday, May 30, 2019 11:42AM - 11:54AM |
P04.00007: Staggered-immersion cooling of a quantum gas in optical lattices Zhen-Sheng Yuan, Bing Yang, Hui Sun, Chun-Jiong Huang, Han-Yi Wang, You-Jin Deng, Han-Ning Dai, Jian-Wei Pan Cooling many-body systems to ultralow temperatures has revolutionized the field of quantum physics. In the nanokelvin regime, strongly correlated quantum gases in optical lattices provide a clean and controllable platform for studying complex many-body problems. However, the central challenge towards revealing exotic phases of matter and creating robust multi-particle entangled states is to further reduce the thermal entropy of such systems. Here we realize efficient cooling of ten thousand ultracold bosons in staggered optical lattices. By immersing Mott-insulator samples into removable superfluid reservoirs, thermal entropy is extracted from the system. Losing only less than half of the atoms, we lower the entropy of a Mott insulator by 65-fold, achieving a record-low entropy per particle of 0.0019 $k_{\mathrm{B}}$ ($k_{\mathrm{B}}$ is the Boltzmann constant). We further engineer the samples to a defect-free array of isolated single atoms and successfully transfer it into a coherent many-body state. This uniform controllable system with over ten thousand addressable qubits can be used for generating large and robust entangled states. For the gapless fermionic phases, our method could dramatically improve the efficiency of entropy transport, giving access to lower-temperature regimes for observing the d-wave superfluid phase. This method opens up an avenue for exploring novel quantum matters and promises practical applications in quantum information science. [Preview Abstract] |
Thursday, May 30, 2019 11:54AM - 12:06PM |
P04.00008: Non-equilibrium fixed point of a driven-dissipative model: A tale of two Ising systems Mohammad Maghrebi, Jeremy Young, Alexey Gorshkov, Michael Foss-Feig Driven-dissipative systems, characterized by a fast external drive as well as a coupling to a dissipative bath, are not only relevant to a vast range of experimental platforms, but also pose fundamental questions about the nature of non-equilibrium states and dynamics. In this talk, I will discuss a driven-dissipative system of bosons that can be mapped to a system of two coupled Ising-like order parameters at different effective temperatures. I will argue that this model possesses a new non-equilibrium fixed point with features that have no counterpart in equilibrium. Specifically, a generic continuous scale invariance at criticality is reduced to a discrete scale invariance. This will further result in complex-valued critical exponents, a spiraling phase boundary, and a complex Liouvillian gap even close to the phase transition. As direct evidence of the non-equilibrium nature of the fixed point, we find that the fluctuation-dissipation relation is violated at all scales, leading to an effective temperature that becomes ``hotter'' and ``hotter'' at longer and longer wavelengths. I will also discuss how a system of cavity arrays with cross-Kerr nonlinearities enables the observation of this non-equilibrium behavior. [Preview Abstract] |
Thursday, May 30, 2019 12:06PM - 12:18PM |
P04.00009: Modeling matter-wave emission into a structured vacuum Michael Stewart, Joonhyuk Kwon, Dominik Schneble The implementation of matter-wave based open quantum systems [1] provides access to novel emission behaviors beyond the usual Markovian treatment. In this talk we theoretically analyze the effects of introducing an emission vacuum with a band structure mirroring that of a photonic crystal. We calculate the exotic decay dynamics arising from the analytic structure of the system’s self energy. We find the existence of two poles outside the band corresponding to bound states above and below the band, and investigate their dynamical signatures in the time evolution of the emitted matter-wave population. \newline \newline [1] L. Krinner, M. Stewart, A. Pazmiño, J. Kwon, D. Schneble, Nature \textbf{559}, 589 (2018) [Preview Abstract] |
Thursday, May 30, 2019 12:18PM - 12:30PM |
P04.00010: Towards Controlled Free-Electron Decoherence Wayne Huang, Zilin Chen, Herman Batelaan We report on our preliminary results from an experiment that is designed for studying controlled free-electron decoherence. Using above band-gap or below band-gap photoexcitation, we created various charge patterns on the surface of an undoped GaAs plate. Through Coulomb interaction with the surface charges, a diffracted electron wavepacket is coupled to the plate in such a way that the resulting beam pattern is either displaced or deformed depending on the state of the light-induced surface charges. The low electron beam flux guarantees that only one electron is present in the vacuum chamber at any given time. As such, we devised an open quantum system that consists of single electrons coupled to a semiconductor plate. In this talk, I will discuss the observed contrast loss and broadening of the diffraction peaks. Possible mechanisms that may lead to such effects, including decoherence, will be reviewed. [Preview Abstract] |
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