Bulletin of the American Physical Society
APS March Meeting 2015
Volume 60, Number 1
Monday–Friday, March 2–6, 2015; San Antonio, Texas
Session S36: Focus Session: Driven Systems and Quench Dynamics In Interacting Bosons |
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Sponsoring Units: DAMOP Chair: Eugene Demler, Harvard University Room: 211 |
Thursday, March 5, 2015 8:00AM - 8:12AM |
S36.00001: Non-equilibrium dynamics of atomic Fermi and Bose gas under lattice geometry transformation Chen-Yen Lai, Chih-Chun Chien The tunability of ultra-cold atom experiments has provide a new arena of exploring quantum effect in both bosonic and fermonic system in and out of equilibrium. According to recent experiments [Phys. Rev. Lett. 108, 045305 (2012).], a triangular lattice can be dynamically tuned into a square or kagome lattice by adjusting frequency and focus point of laser beams. We simulate the dynamical properties of single component fermions and weakly interacting bosons under various transformation processes, including different ramping time scales, different ramping functions, and more importantly into different types of lattice geometry. A non-equilibrium steady state, which is not thermalized, is found in single component fermion system under different particle densities in both small size system and in the thermodynamic limit. In contras, weakly interacting bosons do not exhibit observable steady state behavior. This opens new opportunities of research on dynamical multi-band effects. [Preview Abstract] |
Thursday, March 5, 2015 8:12AM - 8:24AM |
S36.00002: Spatio-temporal correlations in the Bose Hubbard model after a quantum quench Matthew Fitzpatrick, Malcolm Kennett The dynamics of the Bose Hubbard model after a quantum quench have attracted much recent attention. Theoretically, it has proven challenging to describe spatio-temporal correlations in dimensions higher than one. We use the Schwinger-Keldysh technique and a strong coupling expansion to develop a two particle irreducible formalism that allows the study of correlations in time and space in both superfluid and Mott insulating regimes after a quantum quench. We obtain equations of motion for two-time correlation functions and relate our results to recent cold-atom experiments. [Preview Abstract] |
Thursday, March 5, 2015 8:24AM - 8:36AM |
S36.00003: Trap-induced scales in non-equilibrium dynamics of strongly interacting bosons Rajdeep Sensarma, Anirban Dutta, Krishnendu Sengupta We use a time-dependent hopping expansion technique to study the non-equilibrium dynamics of strongly interacting bosons in an optical lattice in the presence of a harmonic trap characterized by a force constant K. We show that after a sudden quench of the hopping amplitude $J$ across the superfluid (SF)-Mott insulator(MI) transition, the SF order parameter $\Delta_r(t)$ and the local density fluctuation $\delta n_r(t)$ exhibit sudden decoherence beyond a trap-induced time scale $T_0 \sim K^{-1/2}$. We also show that after a slow linear ramp down of $J$, $ \Delta_r$ and the boson defect density $P_r$ display a novel non-monotonic spatial profile. Both these phenomena can be explained as consequences of trap-induced time and length scales affecting the dynamics and can be tested by concrete experiments. [Preview Abstract] |
(Author Not Attending)
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S36.00004: Critical Dynamics of Spontaneous Symmetry Breaking in a Homogeneous Bose Gas Nir Navon, Alexander Gaunt, Robert Smith, Zoran Hadzibabic We explore the dynamics of spontaneous symmetry breaking in a homogeneous system by thermally quenching an atomic gas with short-range interactions through the Bose-Einstein phase transition. Using homodyne matter-wave interferometry to measure first-order correlation functions, we verify the central quantitative prediction of the Kibble-Zurek theory, namely the homogeneous-system power-law scaling of the coherence length with the quench rate. Moreover, we directly confirm its underlying hypothesis, the freezing of the correlation length near the transition due to critical slowing down. Our measurements agree with beyond mean-field theory, and support the previously unverified expectation that the dynamical critical exponent for this universality class, which includes the $\backslash $lambda-transition of liquid 4He, is z$=$3/2. [Preview Abstract] |
Thursday, March 5, 2015 8:48AM - 9:00AM |
S36.00005: Quench dynamics of a strongly interacting resonant Bose gas Xiao Yin, Leo Radzihovsky We explore the dynamics of a resonant Bose gas following its quench to a strongly interacting regime near a Feshbach resonance. For such deep quenches, we utilize a self-consistent dynamic mean-field approximation and find that after an initial regime of many-body Rabi-like oscillations between the condensate and finite-momentum quasiparticle pairs, at long times, the gas reaches a prethermalized nonequilibrium steady state. We explore the resulting state through its broad stationary momentum distribution function, that exhibits a power-law high momentum tail. We study the associated enhanced depletion, quench-rate dependent excitation energy, Tan's contact, structure function and radio frequency spectroscopy. We find these predictions to be in a qualitative agreement with recent experiments [Preview Abstract] |
Thursday, March 5, 2015 9:00AM - 9:12AM |
S36.00006: Dynamics of a driven quantum gas: Non-hermiticity, pseudo-spectra and phase transitions Konstantinos Makris, Manas Kulkarni, Hakan Tureci System of an optically driven quantum gas coupled to a single mode of a leaky cavity offers a unique platform to study open quantum systems. This system displays two exceptional points and a quantum critical point when the drive strength (equivalently, the light-matter coupling) is tuned. Here, we study [1] the non-normal properties of this system especially near these special points. Adapting the rich mathematics behind the theory of pseudo-spectra, we characterize the open quantum phase transitions in this system by studying the fluctuations. Our method offers a novel way to understand physics near criticality beyond the traditional approach of arriving at a phase diagram using the semi-classical solutions arising from a mean field approach. We further show that the quench dynamics of a driven dissipative quantum gas displays a non-Markovian dynamics featuring substantial transient amplification of the photon flux near the critical point. We also investigate the non-Hermitian physics behind two-operator products thereby shining light on higher order quantum correlations in an open quantum system.\\[4pt] [1] M. Kulkarni, K. G. Makris, H. E. Tureci (2014) [Preview Abstract] |
Thursday, March 5, 2015 9:12AM - 9:48AM |
S36.00007: ABSTRACT WITHDRAWN |
Thursday, March 5, 2015 9:48AM - 10:00AM |
S36.00008: Quantum phase transition in shaken optical lattices Jiao Miao, Boyang Liu, Wei Zheng Lattice shaking technique generates phonon modes coupling different Bloch bands resonantly. For 1D case, in which shaking is along only one direction, experimental observation of effective ferromagnetic domain has been explained by Ising transition. Inspired by these, we generalize to 2D case, in which shaking is along two orthogonal directions. Analogy to 1D case, we find quantum phase transition from normal superfluid(NSF) phase to $D_{4} $ symmetry breaking superfluid($D_{4} $SF) phase. And interaction effect is confirmed to be one factor responsible for modified critical shaking amplitude. We demonstrate, unlike 1D case, shaking types can modify critical shaking amplitude. We introduce a low-energy effective field theory to study quantum criticality of bosons near the tri-critical point between NSF, $D_{4} $SF and MI phases. Furthermore, we show Bose-Einstein condensation can be turned into non-condensed Bose gases by tuning shaking amplitude to the critical value. [Preview Abstract] |
Thursday, March 5, 2015 10:00AM - 10:12AM |
S36.00009: Emergence of dynamical edge-state instabilities in 2D interacting bosonic systems Bogdan Galilo, Ryan Barnett, Derek Lee The emergence of dynamical (edge) instabilities in two-dimensional interacting Boson systems which exhibit edge-states is proposed. In particular, with the Hofstadter model it is shown that a bosonic system can be prepared to have unstable edge states while having stable bulk states. This leads to a fast population of edge-states, a likely observable effect in optical lattice experiments of ultra cold atoms. The presence of a non-trivial topological band structure suggests that the effect might to be robust. [Preview Abstract] |
Thursday, March 5, 2015 10:12AM - 10:24AM |
S36.00010: Controlling the condensate in driven optical lattices Alberto Nocera, Adrian Feiguin We study the one-dimensional attractive Hubbard model under the influence of a periodic driving potential with the time-dependent density matrix renormalization group showing that the system can be driven in an unconventional paired state characterized by a condensate made of Cooper-pairs with a finite center-of-mass momentum similar to a Fulde-Ferrell state. We obtain results both in the laboratory and the rotating reference frames demonstrating that the momentum of the condensate can be finely tuned by changing the ratio between the amplitude and the frequency of the driving. In particular, by quenching the above ratio to the value giving suppression of the tunneling and putting the Coulomb interaction strength to zero, we are able to ``freeze'' the condensate. We finally study the effects of different initial conditions, and compare our numerical results to those obtained from a time-independent Floquet theory in the large frequency regime. Our work offers the possibility of engineering and controlling unconventional paired states in fermionic condensates. [Preview Abstract] |
Thursday, March 5, 2015 10:24AM - 10:36AM |
S36.00011: Dissipative effects in dipolar, quantum many-body systems Arghavan Safavi-Naini, Barbara Capogrosso-Sansone, Ana Maria Rey We use Quantum Monte Carlo simulations, by the Worm algorithm, to study the ground state phase diagram of two-dimensional, dipolar lattice bosons where each site is coupled, via density operators, to an external reservoir. A recent related study of the XXZ model with ohmic coupling to an external reservoir reported the existence of a bath-induced Bose metal phase in the ground state phase diagram away from half filling, and a Luttinger liquid and a charge density wave at half-filling [1]. Our work extends this methodology to higher dimensional systems with long-range interactions. In the case of hard-core bosons, our method can be applied to experimental systems featuring dipolar fermionic molecules in the presence of losses. This work utilized the Janus supercomputer, which is supported by the NSF (award number CNS-0821794) and the University of Colorado Boulder, and is a joint effort with the University of Colorado Denver and the National Center for Atmospheric Research, as well as OU Supercomputing Center for Education and Research (OSCER) at the University of Oklahoma.\\[4pt] [1] Zi Cai, Ulrich Schollwock, Lode Pollet, arXiv:1409.0142 [Preview Abstract] |
Thursday, March 5, 2015 10:36AM - 10:48AM |
S36.00012: ABSTRACT WITHDRAWN |
Thursday, March 5, 2015 10:48AM - 11:00AM |
S36.00013: Evolutionary games of condensates in driven and dissipative bosonic systems Johannes Knebel, Markus F. Weber, Torben Kr\"uger, Erwin Frey Condensation is a collective behavior of particles observed in both classical and quantum physics. For example, when an equilibrated, dilute gas of bosonic particles is cooled to a temperature near absolute zero, the ground state becomes macroscopically occupied (Bose-Einstein condensation). Whether novel condensation phenomena occur far from equilibrium is a topic of vivid research. Only recently has it been proposed that a driven and dissipative gas of bosons can condense not only into a single, but also into multiple non-degenerate states. This phenomenon may occur when a system of non-interacting bosons is weakly coupled to a reservoir and is driven by an external time-periodic force (Floquet system). Coherence becomes negligible and the condensation is described by a Pauli master equation, which also arises in the evolutionary dynamics of classical agents. In our work, we apply concepts from evolutionary dynamics to determine the states that become condensates. This condensate selection is guided by the vanishing of relative entropy production. We find that the system of condensates never comes to rest: The occupation numbers of condensates oscillate, which we demonstrate for a rock-paper-scissors game of condensates. [Preview Abstract] |
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