Bulletin of the American Physical Society
46th Annual Meeting of the APS Division of Atomic, Molecular and Optical Physics
Volume 60, Number 7
Monday–Friday, June 8–12, 2015; Columbus, Ohio
Session C8: Quantum Sychronization & Nonequilibrium Dynamics |
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Chair: Justin Bohnet, National Institute of Standards and Technology Room: Franklin CD |
Tuesday, June 9, 2015 2:00PM - 2:12PM |
C8.00001: Synchronization in Superradiant Lasers Kevin Cox, Joshua Weiner, Justin Bohnet, James Thompson Superradiant (or bad-cavity) lasers based on highly forbidden transitions in cold atoms are expected to produce light with coherence properties exceeding the state-of-the-art, finding applications in optical atomic clocks and other precision measurements. We study experimentally and theoretically the response of a superradiant Raman laser to an applied coherent drive. We observe two forms of synchronization (injection locking) between the superradiant ensemble and the applied drive: one attractive and one repulsive in nature, in which the atomic spin degrees of freedom play a crucial role in determining the dynamics. Additionally, we present time dynamics and steady state behavior of two interacting superradiant lasers. Understanding the synchronization physics of superradiant lasers could inform future implementations with technologically relevant phase noise properties and explorations for understanding synchronization in a quantum regime. [Preview Abstract] |
Tuesday, June 9, 2015 2:12PM - 2:24PM |
C8.00002: Quantum Synchronization of three-level atoms Peiru He, Ana Maria Rey, Murray Holland Recent studies show that quantum synchronization, the spontaneous alignment of the quantum phase between different oscillators, can be used to build superradiant lasers with ultranarrow linewidth. We theoretically investigate the effect of quantum synchronization on many coupled three-level atoms where there are richer phase diagrams than the standard two-level system. This three-level model allows two-color ultranarrow coherent light to be produced where more than one phase must be simultaneously synchronized. Of particular interest, we study the V-type geometry that is relevant to current ${}^{87}Sr$ experiments in JILA. As well as the synchronization phenomenon, we explore other quantum effects such as photon correlations and squeezing. [Preview Abstract] |
Tuesday, June 9, 2015 2:24PM - 2:36PM |
C8.00003: Hamiltonian mechanics limits microscopic engines James Anglin, Lukas Gilz, Eike Thesing We propose a definition of fully microscopic engines (micro-engines) in terms of pure mechanics, without reference to thermodynamics, equilibrium, or cycles imposed by external control, and without invoking ergodic theory. This definition is pragmatically based on the observation that what makes engines useful is energy transport across a large ratio of dynamical time scales. We then prove that classical and quantum mechanics set non-trivial limits--of different kinds--on how much of the energy that a micro-engine extracts from its fuel can be converted into work. Our results are not merely formal; they imply manageable design constraints on micro-engines. They also suggest the novel possibility that thermodynamics does not emerge from mechanics in macroscopic regimes, but rather represents the macroscopic limit of a generalized theory, valid on all scales, which governs the important phenomenon of energy transport across large time scale ratios. We propose experimental realizations of the dynamical mechanisms we identify, with trapped ions and in Bose-Einstein condensates (``motorized bright solitons''). [Preview Abstract] |
Tuesday, June 9, 2015 2:36PM - 2:48PM |
C8.00004: Energy dependent 3-body loss in out-of-equilibrium 1D Bose gases Laura Zundel, Lin Xia, Joshua Wilson, Jean-Felix Riou, David Weiss We measure the three-body loss of out-of-equilibrium one-dimensional (1D) Bose gases and find that it depends strongly on the average energy of the distribution. The theory of three-body loss in 1D gas experiments is incomplete due to the challenge of calculating how correlations evolve. We present an empirical model based on energy dependent correlations and show that it reproduces the data. [Preview Abstract] |
Tuesday, June 9, 2015 2:48PM - 3:00PM |
C8.00005: Undamped Nonequilibrium Dynamics of a Bose Gas in a 3D Isotropic Trap Victor Colussi, Cameron Straatsma, Dana Z. Anderson, Murray Holland In 1909 Boltzmann predicted a curious class of nonequilibrium solutions describing the undamped breathing mode oscillation of a 3D classical gas under isotropic harmonic confinement. His prediction and equation by the same name also famously predated the experimental confirmation of the existence of atoms. In the context of Bose gases in the ultracold regime, we investigate the possibility of studying such a nonequilibrium motion of the cloud persisting indefinitely throughout a range of temperatures above and below the transition and over a range of collisional regimes given a realistic trapping scenario. For a nondegenerate Bose gas, we characterize the emergence of anomalous damping in the breathing mode by modeling the influence of the trap anharmonicities via the joint mechanisms of dephasing and collisional relaxation. The model is tested using recent results from the JILA TOP trap experiment with a non degenerate cloud of Rb87 atoms. This work was supported by the U. S. National Science Foundation and AFSOR. [Preview Abstract] |
Tuesday, June 9, 2015 3:00PM - 3:12PM |
C8.00006: Nonequilibrium dynamics and spin segregation in trapped gases Andrew P. Koller, Joshua Mundinger, Michael L. Wall, Ana Maria Rey We consider harmonically trapped spin-1/2 gases quenched far from equilibrium by a Ramsey pulse. A magnetic field gradient is applied to the trapped gas, resulting in different trapping potentials for the two spin species. We model the dynamics using an effective spin model Hamiltonian with long range interactions, and use the spin model to understand the results of several experiments on spin diffusion and spin segregation in trapped gases. [Preview Abstract] |
Tuesday, June 9, 2015 3:12PM - 3:24PM |
C8.00007: Longitudinal spin diffusion in a nondegenerate Bose gas Jeffrey McGuirk, Dorna Niroomand, Sean Graham We present results from studies of longitudinal spin diffusion of two pseudo-spin domains in a trapped $^{87}$Rb sample above quantum degeneracy, and investigate the effect of the degree of coherence in the domain wall on the dynamics of the system is investigated. Coherence in the domain wall leads to transverse-spin-mediated longitudinal spin diffusion that is slower than classical predictions, as well as altering the domains' oscillation frequency. This spin-system also shows an instability in the longitudinal spin dynamics as the longitudinal and transverse spin components couple, and a conversion of longitudinal spin to transverse spin is observed, resulting in an increase in the total amount of coherence in the system. [Preview Abstract] |
Tuesday, June 9, 2015 3:24PM - 3:36PM |
C8.00008: The effect of adiabaticity on strongly quenched Bose Einstein Condensates Hong Ling, Ben Kain We study the properties of a Bose-Einstein condensate following a deep quench to a large scattering length during which the condensate fraction n$_{\mathrm{c}}$ changes with time. We construct a closed set of equations that highlight the role of the adiabaticity or equivalently, dn$_{\mathrm{c}}$/dt, the rate change of n$_{\mathrm{c}}$, which is to induce an (imaginary) effective interaction between quasiparticles. We show analytically that such a system supports a steady state characterized by a constant condensate density and a steady but periodically changing momentum distribution, whose time average is described exactly by the generalized Gibbs ensemble. We discuss how the n$_{\mathrm{c}}$ -induced effective interaction, which cannot be ignored on the grounds of the adiabatic approximation for modes near the gapless Goldstone mode, can significantly affect condensate populations and Tan's contact for a Bose gas that has undergone a deep quench. In particular, we find that even when the Bose gas is quenched to unitarity, n$_{\mathrm{c}}$(t) does not completely deplete, approaching, instead, to a steady state with a finite condensate fraction. [Preview Abstract] |
Tuesday, June 9, 2015 3:36PM - 3:48PM |
C8.00009: Correlated energy transfer between two ultracold atomic species Sven Kr\"onke, Johannes Kn\"orzer, Peter Schmelcher We study a single atom as an open quantum system, which is initially prepared in a coherent state of low energy and oscillates in a one-dimensional harmonic trap through an interacting ensemble of $N_A$ bosons, held in a displaced trap [{\it arXiv:1410.8676}]. The non-equilibrium quantum dynamics of the total system is simulated by means of an {\it ab-initio} method, giving us access to all properties of the open system and its finite environment. In this talk, we focus on unraveling the interplay of energy exchange and correlations between the subsystems, which are coupled in such a spatio-temporally localized manner. We show that an inter-species interaction-induced level splitting accelerates the energy transfer between the atomic species for larger $N_A$, which becomes less complete at the same time. System-environment correlations prove to be significant except for times when the excess energy distribution among the subsystems is highly imbalanced. These correlations result in incoherent energy transfer processes, which accelerate the early energy donation of the single atom. By analyzing correlations between intra-subsystem excitations, certain energy transfer channels are shown to be (dis-)favored depending on the instantaneous direction of transfer. [Preview Abstract] |
Tuesday, June 9, 2015 3:48PM - 4:00PM |
C8.00010: The assistance of molecular vibrations on coherent energy transfer in photosynthesis from the view of quantum heat engine Zhedong Zhang, Jin Wang Recently the quantum nature in the energy transport in solar cell and light-harvesting complexes have attracted much attention, by being triggered by the experimental observations. We model the light-harvesting complex (i.e., PEB$_{50}$ dimer) as a quantum heat engine and study the effect of the undamped intra-molecule vibrational modes on the coherent energy transfer and quantum transport. Possibly this system can be artificially simulated by atom-cavity setup. We find that the exciton-vibration interaction has non-trivial contribution to the promotion of quantum yield as well as transport properties of the quantum heat engine at steady state, by enhancing the quantum coherence quantified by entanglement entropy. The perfect quantum yield over 90\% has been obtained, assisted by exciton-vibration coupling. We attribute these improvements to the renormalization of the electronic couplings effectively induced by exciton-vibration interaction and the subsequent delocalization of excitons. Finally we demonstrate that the thermal relaxation and dephasing can help the excitation energy transfer in PEB$_{50}$ dimer. [Preview Abstract] |
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