Bulletin of the American Physical Society
42nd Annual Meeting of the APS Division of Atomic, Molecular and Optical Physics
Volume 56, Number 5
Monday–Friday, June 13–17, 2011; Atlanta, Georgia
Session N5: Dynamic and Out-of-Equilibrium Phenomena in Cold Atoms |
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Chair: Josh Zirbel, University of Illinois at Urbana-Champaign Room: A705 |
Thursday, June 16, 2011 10:30AM - 10:42AM |
N5.00001: Universal Spin Transport in Strongly Interacting Fermi Gases Ariel Sommer, Mark Ku, Martin W. Zwierlein We present measurements of the spin transport properties of strongly-interacting two-component Fermi gases (arXiv:1101.0780v1). Spin transport is generated by spatially separating the two spin components in an external potential, and allowing the system to relax to equilibrium. We find that spin drag is greatest when interactions are resonant, while spin diffusivity is minimized on resonance. Varying the temperature on resonance shows that the spin diffusivity approaches a universal minimum set by Planck's constant and the atomic mass. From the spin transport measurements we determine the spin susceptibility of the unitary Fermi gas as a function of temperature. In highly polarized Fermi gases with resonant interactions, we observe maximal spin drag at finite temperatures, with a reduction at low temperatures due to Pauli blocking. Finally, we observe strong spin drag in superfluid Fermi gases with small spin polarization. [Preview Abstract] |
Thursday, June 16, 2011 10:42AM - 10:54AM |
N5.00002: Non-equilibrium dissipative dynamics and heating of cold atoms in optical lattices Andrew Daley, Hannes Pichler, Johannes Schachenmayer, Matthias Troyer, Peter Zoller We study the dissipative many-body dynamics of cold atoms in optical lattices induced by heating processes, including spontaneous emissions and noise on the lattice potential. The corresponding heating processes are intrinsically non-equilibrium, and a key aspect of the dynamics is the interplay between the form of the dissipation and the many-body physics of the state present in the system. We discuss how different heating mechanisms will differently affect the characteristic correlation functions of different many-body states, and to what extent states in different parameter regimes are able to thermalise in the presence of dissipation. In 1D we compute the dissipative dynamics from a quantum mechanical master equation numerically by combining time- dependent density matrix renormalization group methods with quantum trajectory techniques. [Preview Abstract] |
Thursday, June 16, 2011 10:54AM - 11:06AM |
N5.00003: Non-Equilibrium Dynamics of 1d Bose Gases Studied via Noise Distributions Michael Gring, Maximilian Kuhnert, Tim Langen, David A. Smith, Takuya Kitagawa, Eugene Demler, Joerg Schmiedmayer Understanding the dynamics of non-equilibrium many-body quantum systems is crucial for many areas in physics. However, due to the many degrees of freedom involved, characterising the dynamics is not an easy task. Here we present a first test of the use of noise distributions to analyse the evolution of a non-equilibrium many-body quantum system. The system under investigation is a coherently split 1d Bose gas. Repeated realizations of the experiment give us access to the noise distributions of the shot to shot variation of the interference pattern for different evolution times. By mapping out these distributions at different length scales, we demonstrate that the multimode character and enhanced role of fluctuations in 1d systems play a dramatic role in the resultant non-equilibrium dynamics. [Preview Abstract] |
Thursday, June 16, 2011 11:06AM - 11:18AM |
N5.00004: Adiabaticty timescales in Optical Lattices Stefan Natu, Erich Mueller, Kaden Hazzard We study the timescales for adiabaticity of trapped cold bosons subject to a time-varying lattice potential using a dynamic Gutzwiller mean-field theory. We explain apparently contradictory experimental observations by demonstrating a clear separation of timescales for local dynamics ($\sim$ ms) and global mass redistribution ($\sim 1$s). We provide a simple explanation for the short and fast timescales, finding that while density/energy transport is dominated by low energy phonons, particle-hole excitations dominate the physics for fast ramps. This is particularly relevant to experiments using bandmapping to probe local observables. Furthermore, we show how mass transport shuts off within Mott domains, causing to a chemical potential gradient within the sample that fails to equilibrate on experimental timescales. [Preview Abstract] |
Thursday, June 16, 2011 11:18AM - 11:30AM |
N5.00005: Interaction Driven Interband Tunneling of Bosons in the Triple Well Peter Schmelcher, Yiannis Brouzos, Sascha Zoellner, Lushuai Cao We study the tunneling of an ensemble of bosons in a triple-well potential with strong repulsive interaction. The usual treatment within the single-band approximation suggests suppression of tunneling in the strong interaction regime. However, we show that several windows of enhanced tunneling are opened in this regime. This enhanced tunneling results from higher band contributions, and has the character of interband tunneling. It can give rise to various tunneling processes, such as single-boson tunneling and two-boson correlated tunneling of the ensemble of bosons, and is robust against deformations of the triple well potential. We introduce a basis of number states including all contributing bands to explain the interband tunneling, and demonstrate various patterns of interband tunneling and its robustness by numerically exact calculation. [Preview Abstract] |
Thursday, June 16, 2011 11:30AM - 11:42AM |
N5.00006: Study of the Bose-Hubbard model by collapse and revival measurements Eite Tiesinga, Philip Johnson We show that collapse and revival experiments with interacting atoms trapped in an optical lattice, based on a suggestion by [1], are a sensitive tool for characterizing its many-body ground state. Collapse and revival experiments involve sudden increases of the lattice depth whereby the system transfers from an initial superfluid ground state to a non-stationary state for a lattice depth where tunneling between sites is negligible. The state then evolves independently in each site for a variable amount of time, after which the momentum distribution is measured. The time evolution of momentum states are then sensitive to the amplitude of the initial atom-number Fock states. We show that for superfluid states away from the Mott insulator phase boundary the evolution has many more frequency components than superfluid states close to this boundary.\\[4pt] [1] S. Will {\it et al.}, Nature {\bf 465}, 7295 (2010). [Preview Abstract] |
Thursday, June 16, 2011 11:42AM - 11:54AM |
N5.00007: Spin wave induced coherence dynamics in an ultracold gas Jeffrey McGuirk, Lydia Zajiczek We demonstrate a technique for driving spin waves with arbitrary spatial modes in a trapped gas of $^{87}$Rb atoms. We study the highly nonlinear nature of these spin waves and show that they can lead to collapse and revival of coherence. In particular, we observe spatially localized collapse and revival of Ramsey fringe contrast and show how the pattern of coherence depends on the strength of the spin-wave excitation. The spatial character of the coherence dynamics is incompatible with a simple model based only on position-space overlap of wave functions, requiring a full phase-space description of the atomic spin using a quantum Boltzmann transport equation. [Preview Abstract] |
Thursday, June 16, 2011 11:54AM - 12:06PM |
N5.00008: Dynamic Scaling Behavior of the Hysteresis Loop Area in a Periodically Modulated Cold Atomic System under Oscillating Bias Field Yonghee Kim, Myoung-Sun Heo, Geol Moon, Ji-Hyoun Kim, Wonho Jhe Measuring the system response to the oscillating bias field is fundamental tool to investigate the dynamic properties of nonequilibrium systems. We demonstrate the dynamic bi-stable states which show mean-field type phase transition using the parametrically modulated magneto-optically trapped Rb atoms. And we realize the bias field in this system by adding the weak additional modulation to the parametric modulation. We measure the system response to the oscillating bias field varying the amplitude and frequency of the bias field. The system shows hysteresis phenomena, and the area of the hysteresis loop shows the dynamic scaling behaviors. The experimental results show that the scaling exponents depend on the total number of atoms. And we observed that the period averaged order parameter shows nonequilibrium criticality called dynamic phase transition. [Preview Abstract] |
Thursday, June 16, 2011 12:06PM - 12:18PM |
N5.00009: Kinetic Phase Transition in a Periodically Perturbed Magneto-Optically Trapped Atoms Far From Equilibrium Geol Moon, Yonghee Kim, Ji-Hyoun Kim, Heung-Ryoul Noh, Wonho Jhe Over the past few decades, the behavior of far from equilibrium systems and role of the fluctuation in nonequilibrium systems have been brought to attention and a considerable number of studies have been conducted in physics, chemistry, and biology. We use the periodically perturbed magneto-optical trapped $^85$Rb atoms to investigate a noise-induced transition in nonlinear dynamical system, especially kinetic phase transition (KPT) which is similar behavior to first-order phase transition in equilibrium systems. The system is described by Duffing oscillation, and it is well-known that the Duffing oscillator undergoes the hysteresis. Within the particular range in frequency of the external driving, there is the bi-stable region which the large and small vibration amplitude coexists. We measure the occupation probability of bi-stable states directly because our system consists of many atoms in contrast to many trials for the measurement for single particle system. A critical region is shown to arise in the vicinity of the KPT point, at which the populations of two stable states are equal, including an appearance of a supernarrow peak in the spectral density of the fluctuations. [Preview Abstract] |
Thursday, June 16, 2011 12:18PM - 12:30PM |
N5.00010: Quantum chaos experiments using interacting atoms in a BEC Rajendra Shrestha, Gil Summy The delta-kicked rotor has been one of the workhorses of both theoretical and experimental studies of quantum chaos. Most experimental work has been accomplished using cold atoms exposed to pulses from standing wave optical potentials. Atoms in these systems are assumed to be independent particles even in experiments done with dilute gasses of Bose-Einstein condensates where atomic collisional interactions can be ignored. Nevertheless, theoretical work has suggested that interactions can play a significant role in modifying the behavior of this system. The presence of atomic collisions adds non-linearity to the Schrodinger equation, making it more reminiscent of classical chaos. We will present results from experiments carried out using Rb87 BECs which have had the atomic interactions manipulated using a Feshbach resonance. [Preview Abstract] |
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