Bulletin of the American Physical Society
50th Annual Meeting of the APS Division of Atomic, Molecular and Optical Physics APS Meeting
Volume 64, Number 4
Monday–Friday, May 27–31, 2019; Milwaukee, Wisconsin
Session V07: Out-of-equilibrium trapped gases |
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Chair: John Thomas, North Carolina State University Room: Wisconsin Center 103AB |
Friday, May 31, 2019 8:00AM - 8:12AM |
V07.00001: Finite Temperature Dynamics of the Kondo Model in Ultracold Alkaline-Earth Atoms Shimpei Goto, Ippei Danshita Rapid development in controlling ultracold alkaline-earth-like atoms has paved a new way to realize quantum simulators of multiorbital many-body systems. Specifically, Ono \textit{et al.} has recently reported the observation of the antiferromagnetic interaction between stable and metastable states of $^{171}$Yb atoms [1], which makes it highly possible to simulate the Kondo model, one of the most fundamental models of multiorbital many-body systems. The characteristic feature of the Kondo model is the anomalous temperature dependence of the electric resistivity, namely the Kondo effect. Here, one practical question arises: How can one observe such an effect in atomic gasses, which are electrically neutral? In this study, we numerically simulate quench dynamics at finite temperatures triggered by the shift of a trap center with the use of matrix product states. We find that the center-of-mass velocity, which can be measured in typical experiments, depends significantly on temperature, and such temperature dependence disappears in fully spin-polarized systems. These results indicate that one can use the center-of-mass velocity as a signal of the Kondo effects. \linebreak \linebreak \noindent [1] K. Ono \textit{et al.,} arXiv:1810.00536 [Preview Abstract] |
Friday, May 31, 2019 8:12AM - 8:24AM |
V07.00002: Breathing Mode of a BEC Repulsively Interacting with a Fermionic Reservoir Isabella Fritsche, Bo Huang, Rianne S. Lous, Cosetta Baroni, Jook T. M. Walraven, Emil Kirilov, Rudolf Grimm We investigate the fundamental breathing mode of a small-sized elongated 41K Bose-Einstein condensate coupled to a large 6Li Fermi sea. This two-species system presents a Feshbach resonance at 335 G between the two lowest Zeeman states of the constituents, which we use to tune the interspecies scattering. We observe a signifcant frequency up-shift of the breathing mode when the mixture undergoes phase separation at strong repulsion. The maximum shift, which occurs in the full phase-separation limit, depends essentially on the atom number ratio of the components. Our interpretation of the experimental observations consist of two models that are valid in different regimes of the interaction strength. We describe the weakly interacting regime by assuming an adiabatic response of the Fermi sea, whereas for the fully phase-separated mixture we consider single fermion trajectories. These two complementary models capture the observed features over the full range of interest. [Preview Abstract] |
Friday, May 31, 2019 8:24AM - 8:36AM |
V07.00003: Kibble-Zurek universality in a strongly interacting Fermi superfluid Jee Woo Park, Bumsuk Ko, Kyuhwan Lee, Yong-il Shin Near a continuous phase transition, systems with different microscopic origins display universal dynamics if their underlying symmetries are compatible. In the Kibble-Zurek (KZ) mechanism, a thermally quenched system reveals such dynamics through the creation of topological defects, whose universal nature is encapsulated in a characteristic scaling exponent that describes the dependence of the defect density on the quench rate. Here, we report the observation of the Kibble-Zurek universality in a strongly interacting Fermi superfluid. A linear temperature quench applied to an oblate sample of $^{6}$Li atoms near a Feshbach resonance creates as many as 50 vortices in the superfluid phase, and their counting statistics reveals the characteristic power-law scaling of the KZ mechanism. Importantly, as the systemâ€™s microscopic description is tuned from bosonic to fermionic, the KZ exponent remains constant at a value that is consistent with the inhomogeneous KZ mechanism for a BEC in a harmonic trap, revealing the underlying $U(1)$ gauge symmetry of the system. However, when the quench rate is sufficiently increased, the destructive collisions among vortices limit the vortex density to a value that is inversely proportional to the interaction dependent area of the vortex cores. [Preview Abstract] |
Friday, May 31, 2019 8:36AM - 8:48AM |
V07.00004: Observing hydrodynamic linear response in a uniform Fermi gas Lorin Baird, Xin Wang, Stetson Roof, John Thomas We create a nearly uniform Fermi gas in a box-shaped repulsive optical potential. A spatially periodic optical potential of chosen wavelength is moved through the gas with a selected speed between subsonic and supersonic. We measure the linear hydrodynamic response of the density and numerically simulate the spatial profile to determine the relative contributions of shear viscosity and thermal conductivity. [Preview Abstract] |
Friday, May 31, 2019 8:48AM - 9:00AM |
V07.00005: Spiral Bose Fireworks: parametric amplification of vortex states Han Fu, Jooheon Yoo, Lei Feng, Cheng Chin, Kathryn Levin Periodic modulation of the two-body interaction in a Bose condensate has led to the interesting observation of ``Bose fireworks'' [Nature 551, 356 (2017)]; these were later shown to be well captured by our time-dependent Gross-Pitaevskii simulations [Phys. Rev. Lett. 121, 243001 (2018)]. The goal of these experiments is to unravel the structure of an unknown condensate through parametric amplification. To fulfill this, we discuss simulated emission patterns of complex initial states and find intriguing jet trajectories. Spiral jets are seen when vortices are imprinted into the initial condensate. This story, interestingly, can serve as a quantum version of the water beam emission by a sprinkler. We show how one can extract from the spiral pattern information such as the vortex winding number and condensate size. Using this ``phase-tomography'' philosophy, we also study other cases such as divided condensates so that one half is phase-shifted relative to the other. We present a general analytical formalism to describe this amplification process, which in some sense is reminiscent of established procedures in particle physics. [Preview Abstract] |
Friday, May 31, 2019 9:00AM - 9:12AM |
V07.00006: Turbulent cascades in a homogeneous Bose gas with tuneable interactions Jake Glidden, Lena Bartha, Christoph Eigen, Timon Hilker, Robert Smith, Zoran Hadzibabic Turbulence is a complex phenomenon manifest in a myriad of systems, ranging from ocean waves to supernovae. A ubiquitous concept within turbulence is the cascade of excitations through momentum space, between energy-injection and dissipation lengthscales. Over this range, various quantities (e.g. the wave energy) exhibit steady-state power-law distributions in momentum space. Over the past few years ultracold atomic gases have become a novel platform for studies of turbulence. Recent work showed the development of a power-law cascade with an exponent consistent with mean-field predictions. However, so far little is known about the dependence of steady-state properties on the strength of the interactions that are needed to establish the cascade in the first place. Here we explore the effects of inter-particle interactions on the turbulent-cascade dynamics using a homogeneous ${}^{39}\textrm{K}$ Bose gas, which offers tuneable interaction strength via a Feshbach resonance. We find universal behaviour of the turbulent cascade dynamics across a range of different scattering lengths. [Preview Abstract] |
Friday, May 31, 2019 9:12AM - 9:24AM |
V07.00007: Dicke time crystals in driven-dissipative quantum many-body systems Bihui Zhu, Jamir Marino, Norman Yao, Mikhail Lukin, Eugene Demler Recent experimental progress has opened up an opportunity to explore nonequilibrium phenomena in AMO systems, which can exhibit interesting behavior absent in equilibrium, with time crystals---phases of quantum matter that spontaneously break time translational symmetry---as an example. In particular, the paradigmatic Dicke model, which describes an ensemble of atoms collectively coupled to a leaky cavity mode, has recently been shown to host time-crystalline-like behavior of the collective spin in the presence of periodic driving [1]. Here, we investigate the situation where the mean-field solvability of the conventional Dicke model is explicitly broken by the addition of short-range interactions between the atoms. In this context, the interplay between driving, dissipation and interactions yields a rich set of dynamical responses including long-lived and metastable Dicke time crystals. Interestingly, when the additional short-range interactions are ferromagnetic, we observe time crystalline behavior at non-perturbative values of the interaction strength, suggesting the possible existence of stable order in a driven-dissipative quantum many-body system. [1] Z. Gong, R. Hamazaki, and M. Ueda, Phys. Rev. Lett. 120, 040404 (2018) [Preview Abstract] |
Friday, May 31, 2019 9:24AM - 9:36AM |
V07.00008: Routes to maximize the lifetime of discrete time crystals Sayan Choudhury, Qi Zhou Motivated by the recent observation of time crystals in the absence of disorder, we propose schemes to extend the lifetime of a discrete time crystal in a translation invariant Ising spin chain. We derive an analytical framework to show that by appropriately tuning the interactions, it is always possible to observe time crystal signatures in a finite size chain. We also obtain an expression for the optimal value of the Ising interaction that maximizes the lifetime of the time crystal. Our results hold for both short and long range interacting systems. Furthermore, we find that in the thermodynamic limit, only an infinite range interaction can lead to a time crystal in the absence of disorder. Our work elucidates the crucial role of interactions in realizing a time crystal. [Preview Abstract] |
Friday, May 31, 2019 9:36AM - 9:48AM |
V07.00009: Local spin manipulation of quantized atomic currents Laura Corman, Martin Lebrat, Samuel H\"{a}usler, Philipp Fabritius, Dominik Husmann, Tilman Esslinger Controlling the internal state of a particle in an ultracold atom experiment is instrumental for studying spinor phases and most prominently to emulate spin transport and artificial gauge fields. This control can be implemented using magnetic fields --- acting on the full cloud --- or using light fields --- which can be spatially varied. The latter method was successfully used in several experiments to couple the spin and motional degrees of freedom of quantum gases, although the experiment time was strongly constrained by the heating induced by the laser beams. \newline Here, we report on the control of spin transport of fermionic lithium atoms at a quantum point contact thanks to the spatial shaping of a near-resonant laser. Spin-dependent transport was observed over several seconds with reduced heating thanks to the localized spin potential. We were able to lift the spin degeneracy for weak interactions while retaining conductance plateaus. The observed conductances match a Landauer theory adapted to take losses into account. We were finally able to distinguish small changes in the interaction strength by monitoring the separation between the two spin conductance curves. [Preview Abstract] |
Friday, May 31, 2019 9:48AM - 10:00AM |
V07.00010: Spin- and atom-interactions in multimode cavity QED Ronen Kroeze, Yudan Guo, Jonathan Keeling, Benjamin Lev Optical cavity QED provides a versatile platform with which to explore quantum many-body physics in driven-dissipative systems. Multimode cavities are particularly apt for exploring beyond mean-field physics. After previously having demonstrated strong, tunable range, photon-mediated, atom-atom interactions, we now present three other recent experimental advances. Firstly, we have endowed these interactions with a sign-changing feature. In a confocal cavity, Gouy phase effects result in non-local, sign-changing interactions, and enriched symmetries. We demonstrate this using holographic detection of the cavity emission, after crossing a superradiant, self-organization phase transition. In the same context of a non-equilibrium Dicke-like phase transition, we realize joint spin-spatial (spinor) organization of a two-component Bose-Einstein condensate, as driven by spinor-spinor interactions. Lastly, we present results on dynamical spin-orbit coupling, where a chiral spin spiral emerges. Uniquely, it is quantum fluctuations that drive this spin-orbit coupling, enabling studies of dynamical gauge fields. Together, these advances enable us to explore exotic, strongly correlated systems such as quantum liquid crystals, driven-dissipative spin glasses, and quantum neural networks. [Preview Abstract] |
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