Bulletin of the American Physical Society
APS March Meeting 2011
Volume 56, Number 1
Monday–Friday, March 21–25, 2011; Dallas, Texas
Session Q45: Non-equilibrium Physics with Cold Quantum Gases II |
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Sponsoring Units: DAMOP Chair: Eite Tiesinga, National Institute of Standards and Technology Room: A310 |
Wednesday, March 23, 2011 11:15AM - 11:27AM |
Q45.00001: Quenched dynamics in interacting one-dimensional systems: Appearance of current carrying steady states from initial domain wall density profiles Jarrett Lancaster, Emanuel Gull, Aditi Mitra Dynamics arising after an interaction quench in the quantum sine-Gordon model is studied for the case of a system initially prepared in a spatially inhomogeneous domain wall state. The time-evolution of the density, current and equal time correlation functions are studied using the truncated Wigner approximation (TWA) to which quantum corrections are added in order to set the limits on its validity. For weak to moderate strengths of the back-scattering interaction, the domain wall is found to spread out ballistically with the system within the light cone reaching a non-equilibrium steady-state characterized by a net current flow. A steady state current is also found to exist for a quench at the exactly solvable Luther-Emery point. The magnitude of the current decreases with increasing strength of the back-scattering interaction. The two-point correlation function of the variable canonically conjugate to the density reaches a steady state which is spatially oscillating at a wavelength which is inversely related to the current. [Preview Abstract] |
Wednesday, March 23, 2011 11:27AM - 11:39AM |
Q45.00002: Quantum quenches and off-equilibrium dynamical transition in the infinite dimensional Bose Hubbard model Giulio Biroli, Bruno Sciolla We study the off-equilibrium dynamics of the infinite dimensional Bose Hubbard Model after a quantum quench. The dynamics can be analyzed exactly by mapping it to an effective Newtonian evolution. For integer filling, we find a dynamical transition separating regimes of small and large quantum quenches starting from the superfluid state. This transition is very similar to the one found for the fermionic Hubbard model by mean field approximations. [Preview Abstract] |
Wednesday, March 23, 2011 11:39AM - 11:51AM |
Q45.00003: Optimal control for unitary preparation of many-body states: application to Luttinger liquids Armin Rahmani, Claudio Chamon Many-body ground states of local Hamiltonians can be prepared via unitary evolution in cold atomic systems. Given the initial state and a fixed time for the evolution, how close can we get to a desired ground state if we can tune the Hamiltonian in time? Here we study this optimal control problem focusing on Luttinger liquids with tunable interactions. We show that the optimal protocol can be obtained using the simulated annealing method. Rather surprisingly, we find that in the Luttinger liquid case the interaction strength in the optimal protocol can have a \textit{non-monotonic} time-dependence. We find a marked difference in the behavior of the system when the ratio $\tau/L$ of the preparation time to the system size exceeds a critical value around 1/8. In this regime, the optimal protocol can prepare the states with almost perfect accuracy. Finally, we argue that the time-scale of the optimal evolution defines a dynamical measure of distance between quantum states. [Preview Abstract] |
Wednesday, March 23, 2011 11:51AM - 12:03PM |
Q45.00004: Dissipative Transport of Trapped Bose-Einstein Condensates through Disorder Satyan Bhongale, Paata Kakashvili, Carlos Bolech, Han Pu After almost half a century since the work of Anderson [Phys. Rev. {\bf 109}, 1492 (1958)], at present there is no well established theoretical framework for understanding the dynamics of interacting particles in the presence of disorder. Here, we address this problem for interacting bosons near $T=0$, a situation that has been realized in trapped atomic experiments with an optical speckle disorder. We develop a theoretical model for understanding the hydrodynamic transport of \emph{finite-size} Bose-Einstein condensates through disorder potentials. The goal has been to set up a simple model that will retain all the richness of the system, yet provide analytic expressions, allowing deeper insight into the physical mechanism. Comparison of our theoretical predictions with the experimental data on large-amplitude dipole oscillations of a condensate in an optical-speckle disorder shows striking agreement. We are able to quantify various dissipative regimes of slow and fast damping. Our calculations provide a clear evidence of reduction in disorder strength due to interactions. The analytic treatment presented here allows us to predict the power law governing the interaction dependance of damping. The corresponding exponents are found to depend sensitively on the dimensionality and are in excellent agreement with experimental observations. [Preview Abstract] |
Wednesday, March 23, 2011 12:03PM - 12:15PM |
Q45.00005: Mesoscopic Transport of Ultracold Atoms in Optical Lattices Martin Bruderer, Wolfgang Belzig Transport of quantum gases is attracting considerable attention, both on a theoretical and experimental level, in part because ultracold atoms confined to optical lattices can be coherently manipulated and detected on microscopic scales. In particular, substantial technological progress has opened the way for a bottom-up approach to mesoscopic transport in optical lattices, in which case the coherence in certain parts of the system is deliberately destroyed. We show based on a specific setup, namely two incoherent atomic reservoirs connected by a short optical lattice, that mesoscopic phenomena such as, e.g., phonon assisted transport, coherent suppression of tunneling and non-adiabatic quantum pumping can be realized with ultracold atoms. For our analysis in the tight-binding regime we use the non-equilibrium Green's functions formalism extended to include the time dependence of the reservoirs. [Preview Abstract] |
Wednesday, March 23, 2011 12:15PM - 12:27PM |
Q45.00006: Detecting Paired and Counterflow superfluidity via dipole ocsillations Anzi Hu, Ludwig Mathey, Ippei Danshita, Carl Williams, Charles Clark We study the dynamic response of the paired superfluid (PSF) and counterflow superfluid (CFSF) states in a binary mixture of ultra-cold bosonic atoms following an abrupt displacement of the trapping potential. In the PSF and CFSF states, the pairing and anti-pairing orders lead to novel transport properties and distinctive dynamic responses to the abrupt displacement. The findings provide a clear experimental procedure to detect these orders and give an intuitive insight into the dynamics of paired and counterflow superfluidity. [Preview Abstract] |
Wednesday, March 23, 2011 12:27PM - 12:39PM |
Q45.00007: ABSTRACT WITHDRAWN |
Wednesday, March 23, 2011 12:39PM - 12:51PM |
Q45.00008: Adiabatic Quantum Transport of Bosonic Atoms in Double Well Optical Lattices Yinyin Qian, Chuanwei Zhang Quantum charge pump, where the amount of pumped charges is controlled precisely through the quantized adiabatic charge transport in periodic crystals, has many important applications in electronics. The quantum pump of cold neutral atoms may play a similar significant role in atomtronics. Neutral atoms can be bosons, and their transport properties can be very different from electrons (fermions). We study the adiabatic quantum transport of bosonic atoms in double well optical lattices where the lattice parameters are adiabatically and periodically tuned. The effects of the interaction between atoms on the transport properties are characterized. In the strong interacting regime, the bosonic atoms behave similarly as fermions with quantized atom transport. In the weak interacting regime, the atom transport depends strongly on the paths in the lattice parameter space and the quantized transport may be destroyed. The effects of harmonic traps and disorder potentials are also studied. The investigation is based on the numerical simulation of the exact quantum dynamics of cold atoms in double well optical lattices using the time evolving block decimation algorithm. [Preview Abstract] |
Wednesday, March 23, 2011 12:51PM - 1:03PM |
Q45.00009: Schwinger-Keldysh approach to the Bose-Hubbard model with time varying hopping Malcolm P. Kennett, Denis Dalidovich Cold bosonic atoms confined in an optical lattice potential give a realization of the Bose Hubbard model, and it is possible to study the phase transition between a superfluid and a Mott insulator as the depth of the optical lattice is varied. We study the real time dynamics of the Bose Hubbard model at zero and finite temperature in the presence of time-dependent hopping using the Schwinger-Keldysh technique. Using a strong-coupling approach, we determine the effective action in the vicinity of the zero-temperature transition between superfluid and Mott insulating phases. We then study the solutions of the resulting saddle-point dynamical equations as the hopping is varied to sweep across the phase transition from the superfluid to insulating phase. [Preview Abstract] |
Wednesday, March 23, 2011 1:03PM - 1:15PM |
Q45.00010: Optimal loading for a Tonks-Girardeau gas Claudia De Grandi, Anatoli Polkovnikov We analyze the process of loading a one-dimensional system of hard-core bosons, i.e. a Tonks-Girardeau gas, into a commensurate optical lattice. We consider different loading protocols (e.g. linear, quadratic or sudden ramp in time, or cyclic loading). We discuss possible ways of optimization to minimize the heating and the excitations rate of the system due to the loading process. Combining analytical and numerical methods we analyze the problem under experimentally realistic conditions and we compare the results with earlier scaling predictions. [Preview Abstract] |
Wednesday, March 23, 2011 1:15PM - 1:27PM |
Q45.00011: Weakly interacting bosons in a periodic optical lattice Qinqin Lu, Kelly R. Patton, Daniel E. Sheehy We study an interacting boson gas in a periodic optical potential, with the goal of understanding the properties of such a gas away from the Mott insulating regime at large optical lattice depth. In particular, we analyze the density dependence of the transition temperature as a function of optical lattice depth and the response to a dynamical modulation of the optical lattice. [Preview Abstract] |
Wednesday, March 23, 2011 1:27PM - 1:39PM |
Q45.00012: Pairsuperfluid in Dynamically Constraint Bose-Hubbard Models Lars Bonnes, Stefan Wessel We consider ultra-cold atoms loaded into a two-dimensional optical lattice with strong three-body losses, i.e. three bosons sharing one lattice site scatter inelastically and dissipate from the system. This process dynamically stabilizes a three-body on-site repulsion in analogy to the quantum Zeno effect. The system studied here is described by a Bose-Hubbard model on a square lattice with on- site attraction. The maximal number of particles per lattice site is restricted to two in order to take the three-body repulsion into account. Field theoretical considerations and numerical simulations using Matrix Product States in one dimension suggest the existence of a dimer superfluid phase for small tunneling rates that is effectively described by the condensation of boson pairs and the absence of an atomic condensate. In this work we explore the ground state and finite-temperature phase diagram for our model using large-scale quantum Monte- Carlo simulations. Our main emphasis is the detection of the dimer superfluid phase and we address the issue of extrapolating our finite-temperature data to the thermodyanmic limit at $T = 0$. Furthermore, we explore the possibility of adding an explicit dimer hopping term that drastically changes the behavior of our system. [Preview Abstract] |
Wednesday, March 23, 2011 1:39PM - 1:51PM |
Q45.00013: Beyond mean-field dynamics in open Bose-Hubbard chains Holger Hennig, Dirk Witthaut, Friederike Trimborn, Georgios Kordas, Theo Geisel, Sandro Wimberger We investigate the effects of phase noise and particle loss on the dynamics of a Bose-Einstein condensate in an optical lattice. Starting from the many-body master equation, we discuss the applicability of generalized mean-field approximations in the presence of dissipation and methods to simulate quantum effects beyond mean-field by including higher-order correlation functions. It is shown that localized particle dissipation leads to surprising dynamics, as it can suppress decay and restore the coherence of a Bose-Einstein condensate. These effects can be applied to engineer coherent structures such as stable discrete breathers and dark solitons. [Preview Abstract] |
Wednesday, March 23, 2011 1:51PM - 2:03PM |
Q45.00014: Strong local-field effect on dynamics of a dilute atomic cloud irradiated by two counterpropagating optical fields: beyond standard optical lattices Guangjiong Dong, Jiang Zhu, Weiping Zhang, Mikhail Shneider We study a recent experiment (K. Li et al., Phys. Rev. Lett. 101, 250401 (2008)) on diffracting a Bose-Einstein condensate by two counterpropagating optical fields. Including the local field effect, we explain asymmetric momentum distribution and self-imaging of the BEC in a self-consistent way, and find that the self-imaging is not dependent on the intensity difference of the two optical fields, but on the light-condensate interaction time. We show further that the local field effect leads to deformation of an optical lattice, and thus is essential for getting better quantitative analysis of other current optical lattice experiments of cold atoms. Moreover, intensity imbalance of the two optical fields could be applied as a new means to tailor both cold atom dynamics and optical propagation. [Preview Abstract] |
Wednesday, March 23, 2011 2:03PM - 2:15PM |
Q45.00015: Quenched dynamics in a spin-1/2 chain prepared in a sharp domain wall state Lea Santos, Aditi Mitra, Emil Prodan Using exact diagonalization and Expokit, we study the time evolution of current, magnetization and correlation functions in an isolated spin-1/2 chain initially prepared in a domain wall state. The domain wall consists of spins pointing up in the first half of the chain and down in the other half. Integrable and nonintegrable regimes are reached by adjusting the parameters of the Hamiltonian, which allows for the comparison of behaviors in both limits. In a chain with nearest- neighbor couplings, chaos is induced by adding on-site disorder or by adding next-nearest-neighbor couplings. The magnitude of the current decreases with interaction for the clean integrable system and for the chaotic disordered case. For the chaotic clean system with next-nearest-neighbor couplings, a non- monotonic behavior in the current is found as the interaction strength is increased. [Preview Abstract] |
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