Bulletin of the American Physical Society
48th Annual Meeting of the APS Division of Atomic, Molecular and Optical Physics
Volume 62, Number 8
Monday–Friday, June 5–9, 2017; Sacramento, California
Session G8: Ultracold Gas Dynamics |
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Chair: David Weiss, Pennsylvania State University Room: 314 |
Wednesday, June 7, 2017 8:00AM - 8:12AM |
G8.00001: Imaging transport of ultracold atoms through a quantum wire Samuel Hausler, Martin Lebrat, Dominik Husmann, Laura Corman, Sebastian Krinner, Shuta Nakajima, Jean-Philippe Brantut, Tilman Esslinger We report on a scanning gate technique to experimentally image the transport of fermionic lithium atoms through a quantum wire, similar to what is applied to solid state devices. The gate is created with a tightly focused repulsive laser beam whose aberrations are holographically corrected. By scanning its position over the wire and measuring the subsequent variations of conductance, we spatially map the transport at a resolution close to the transverse wave function of atoms inside the channel. The gate extends on the scale of the Fermi wavelength making it sensitive to quantum tunneling. Furthermore, our knowledge of the optical potential allows a direct comparison with an analytical and a numerical model for non-interacting particles. The flexibility offered by programmable holograms make it relatively simple to imprint more complex structures, such as a one-dimensional lattice inside the wire. This opens the path to study metal-insulator physics with strong attractive interactions. [Preview Abstract] |
Wednesday, June 7, 2017 8:12AM - 8:24AM |
G8.00002: Formation of matter-wave soliton trains by modulational instabillity Jason H. V. Nguyen, De Luo, Randall G. Hulet Matter-wave soliton trains were initially observed following an interaction quench in a condensate of ${^{7}\mathrm{Li}}$ atoms\footnote{K.E. Strecker, G.B. Partridge, A. G. Truscott, \& R. G. Hulet, Nature 417, 150 (2002).}. The solitons in the train were observed to interact repulsively, an indication of a phase difference of $\pi$ between neighboring solitons. Although the formation of soliton trains can be understood as resulting from a modulational instability, an explanation for the observed phase-structure remains elusive. We study the formation of soliton trains by characterizing modulational instability across a wide range of scattering lengths. We find universal scaling laws for the number of solitons created by the quench and for the decay in atom number. Through minimally-destructive imaging, we observe real-time dynamics, and show that soliton trains are created with an alternating phase structure, rather than evolving into one. [Preview Abstract] |
Wednesday, June 7, 2017 8:24AM - 8:36AM |
G8.00003: Quantum Breakup of Higher Order Bright Solitons Lincoln Carr, Christoph Weiss Semiclassical mean field theory in the form of the nonlinear Schrodinger equation (NLS) has had incredible success in modeling the dynamics of repulsive Bose-Einstein condensates (BECs): experimentally observed predictions range from dark solitons to skyrmions. A key prediction for attractive BECs is the bright soliton. An order-two soliton can be produced in a BEC simply by increasing the interaction strength by a factor of four, via a Feshbach resonance. The NLS is exactly solvable in this case and predicts a beautiful time-periodic dynamical pattern. Using matrix-product state methods, we show that such far-from-equilibrium higher order bright solitons exhibit quantum depletion and in fact break up rapidly in the more complete underlying quantum theory. Such break-up presents a smoking gun signal for emergent phenomena in quantum systems that do not have a semiclassical limit, and are therefore truly quantum in nature at macroscopic scales. They also indicate a breakdown of semiclassical integrability at a more fundamental quantum level. [Preview Abstract] |
Wednesday, June 7, 2017 8:36AM - 8:48AM |
G8.00004: Realization of a Tunable Dissipation Scale in a Turbulent Cascade using a Quantum Gas Nir Navon, Christoph Eigen, Jinyi Zhang, Raphael Lopes, Robert Smith, Zoran Hadzibabic Many turbulent flows form so-called cascades, where excitations injected at large length scales, are transported to gradually smaller scales until they reach a dissipation scale. We initiate a turbulent cascade in a dilute Bose fluid by pumping energy at the container scale of an optical box trap using an oscillating magnetic force [1,2]. In contrast to classical fluids where the dissipation scale is set by the viscosity of the fluid, the turbulent cascade of our quantum gas finishes when the particles kinetic energy exceeds the laser-trap depth. This mechanism thus allows us to effectively tune the dissipation scale where particles (and energy) are lost, and measure the particle flux in the cascade at the dissipation scale. We observe a unit power-law decay of the particle-dissipation rate with trap depth, which confirms the surprising prediction that in a wave-turbulent direct energy cascade, the particle flux vanishes in the ideal limit where the dissipation length scale tends to zero. [1] A.L. Gaunt, T.F. Schmidutz, I. Gotlibovych, R.P. Smith, Z. Hadzibabic, Phys. Rev. Lett. 110, 20406 (2013) [2] N. Navon, A.L. Gaunt, R.P. Smith, Z. Hadzibabic, Nature 539, 72 (2016) [Preview Abstract] |
Wednesday, June 7, 2017 8:48AM - 9:00AM |
G8.00005: Exploring extreme nonequilibrium phenomena with trapped atoms Shankari Rajagopal, Ruwan Senaratne, Kevin Singh, Zachary Geiger, Kurt Fujiwara, Peter Dotti, David Weld Trapped ultracold atoms enable direct experimental investigation of nonequilibrium many-body quantum dynamics, including phenomena which are difficult or impossible to investigate in the solid state. We report on progress in two such experiments using ultracold strontium: exploring the excitation structure of phasonic modes in quasicrystals and simulating attosecond-scale electron dynamics. Because phason modes involve long-range rearrangement of atoms, they are typically not dynamical degrees of freedom in solid-state quasicrystals. Uniquely, the cold atom context enables spectroscopic probes of electron-phason coupling. Separately, we discuss quantum emulation of ultrafast physics, which is enabled by equilibration timescales more than ten orders of magnitude slower than those in solids. [Preview Abstract] |
Wednesday, June 7, 2017 9:00AM - 9:12AM |
G8.00006: Quantum memory effects through interaction imbalance in ultracold bosonic and fermonic atoms Chen-Yen Lai, Chih-Chun Chien Memory effects result from history dependent behavior and have board applications. While ground states of noninteracting systems are not expected to exhibit memory effects in dynamic variables such as the mass current, interacting systems can support memory effects which may be measured in novel quantum simulators such as ultracold atoms. Here, we simulate real time dynamics of systems undergo an interaction change only on half of the system using the time-dependent density matrix renormalization group method. The quasi steady state current (QSSC) driven by the interaction imbalance exhibits a plateau lasting for a time period proportional to the system size. By comparing the value of the QSSC from different driving schemes, memory effects can be quantified. Here, two kinds of memory effects induced by interaction imbalance are discussed for both fermionic and boson systems. Starting from different initial states quenched to the same final configurations, memory of the initial quantum state can be observed. Secondly, driving the same initial configuration to the same final configuration linearly with different ramping times further leads to time-dependent memory effects. Those memory effects are from pure quantum origin and we will discuss possible experimental realizations. [Preview Abstract] |
Wednesday, June 7, 2017 9:12AM - 9:24AM |
G8.00007: Observation of quantum-limited spin transport in strongly interacting two-dimensional Fermi gases Ben A. Olsen, Chris Luciuk, Scott Smale, Florian B\"ottcher, Haille Sharum, Stefan Trotzky, Tilman Enss, Joseph H. Thywissen Conjectured quantum bounds on transport appear to be respected in many strongly interacting many-body systems. Since transport occurs as a system relaxes to equilibrium, many such bounds can be recast as an upper bound on the local relaxation rate $k_BT/\hbar$. Systems saturating this ``Planckian'' bound lack well defined quasiparticles promoting transport. We measure the transport properties of 2D ultracold Fermi gases of $^{40}$K during transverse demagnetization in a magnetic field gradient. Using a phase-coherent spin-echo sequence, we distinguish bare spin diffusion from the Leggett-Rice effect, in which demagnetization is slowed by the precession of spin current around the local magnetization. When the 2D scattering length is tuned near an $s$-wave Feshbach resonance to be comparable to the inverse Fermi wave vector $k_F^{-1}$, we find that the bare transverse spin diffusivity reaches a minimum of $1.7(6)\hbar/m$. Demagnetization is also reflected in the growth rate of the $s$-wave contact, observed using time-resolved rf spectroscopy. At unitarity, the contact rises to $0.28(3)k_F^2$ per particle, measuring the breaking of scaling symmetry. Our observations support the conjecture that under strong scattering, the local relaxation rate is bounded from above by $k_BT/\hbar$. [Preview Abstract] |
Wednesday, June 7, 2017 9:24AM - 9:36AM |
G8.00008: Mesoscopic quantum superpositions in bimodal Bose-Einstein condensates: decoherence and strategies to counteract it Krzysztof Pawlowski, Matteo Fadel, Philipp Treutlein, Yvan Castin, Alice Sinatra We study theoretically the interaction-induced generation of small Schrodinger cat states from an initial phase state in bimodal Bose-Einstein condensates. We present a strategy to obtain the cats, despite severe intrinsic and experimental constraints, including particle losses and Poissonian fluctuations of the total particle number. We show that the cat fidelity can be simply deduced from the the subsequent revival. Finally, in a full multimode description, we study the effect of preexisting thermal fluctuations. [Preview Abstract] |
Wednesday, June 7, 2017 9:36AM - 9:48AM |
G8.00009: Quantum Dynamics of Many-Body Systems using Bohmian Trajectories Tarek Elsayed, Klaus Moelmer, Lars Bojer Madsen Several attempts have been made to utilize the Bohmian trajectories as a computational tool to tame the many-body problem in quantum dynamics of large systems. In this work, we develop a new method based on the notion of conditional wavefunctions to solve the time-dependent Schrodinger equation with the help of Bohmian trajctories. This method is used to study the breathing dynamics in a system of bosons. The precision of our method is compared with the Multiconfigurational Time-Dependent Hartree method for Bosons (MCTDHB). [Preview Abstract] |
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