Bulletin of the American Physical Society
49th Annual Meeting of the APS Division of Atomic, Molecular and Optical Physics APS Meeting
Volume 63, Number 5
Monday–Friday, May 28–June 1 2018; Ft. Lauderdale, Florida
Session D09: Transport in Optical Lattices |
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Chair: Ulrich Schneider, University of Cambridge Room: Grand H |
Tuesday, May 29, 2018 2:00PM - 2:12PM |
D09.00001: Bad Metallic Transport in a Cold Atom Fermi-Hubbard System Peter Brown, Debayan Mitra, Elmer Guardado-Sanchez, Peter Schauss, Waseem Bakr Probing the charge transport properties of quantum materials can reveal their unique microscopic properties. Weakly interacting systems such as Fermi liquids are well described by semiclassical Boltzmann transport, but strong interactions blur the particle-like behavior of charge carriers causing this picture to break down. Transport in strongly interacting quantum systems is poorly understood, but exhibits interesting phenomenology in many real materials. In our work, we experimentally study charge conductivity in the Fermi-Hubbard model. Using a quantum gas microscope, we impose a density modulation on a uniform system of ultracold $^6$Li in a 2D optical lattice and observe this modulation decay due to charge diffusion. We find that the decay can be described by a hydrodynamic model and extract the momentum relaxation rate and diffusion constant for a range of temperatures. We determine the conductivity from the diffusion constant using the Nernst-Einstein relation. We observe that the resistivity scales linearly with temperature and shows no sign of saturation for temperatures ranging from near the super-exchange energy scale to the bandwidth. These anomalous behaviors are characteristic of bad metals. [Preview Abstract] |
Tuesday, May 29, 2018 2:12PM - 2:24PM |
D09.00002: Observation of Spin Diffusion in the 2D Fermi-Hubbard Model Matthew Nichols, Melih Okan, Lawrence Cheuk, Enrique Mendez, Thomas Hartke, Hao Zhang, Ehsan Khatami, Martin Zwierlein Quantum gas microscopy of Fermionic systems has allowed for rapid advances in the study of equilibrium properties of the 2D Fermi-Hubbard model. For example, site-resolved measurements have enabled investigations of spatial correlations at variable doping strengths, revealing the intricate interplay between the spin and charge degrees of freedom in these systems. In this talk, we report on a study of spin transport in the Hubbard model using a Fermi gas microscope of ultracold $^{\mathrm{40}}$K atoms trapped in a square optical lattice. Specifically, by preparing a homogeneous Mott-insulating sample at half-filling in the presence of a magnetic gradient, we are able to observe spin dynamics in this strongly correlated regime. By varying the relative strength of the on-site interactions, we explore how they can affect the transport of spin in the system. For a wide range of experimental parameters, we find that the spin dynamics are diffusive in nature, and we can extract the spin diffusion coefficient. These findings are compared with novel numerical linked-cluster expansion (NLCE) calculations. [Preview Abstract] |
Tuesday, May 29, 2018 2:24PM - 2:36PM |
D09.00003: Effect of collisions on the conductivity of fermions in an optical lattice Rhys Anderson, Fudong Wang, Peihang Xu, Vijin Venu, Stefan Trotzky, Frederic Chevy, Joseph Thywissen We explore the effect of varying the interaction strength on the conductivity of fermions in an optical lattice. As described elsewhere [1], we realize the proposal of Wu et al. [2], to determine the global conductivity from in-situ imaging of the displacement of a sample subject to an external periodic forcing. Quantities extracted from such a conductivity measurement include the total spectral weight, given by the integral over the real part of the conductivity spectrum, and the transport lifetime, as determined from the width of the resonance peak. As the scattering length increases near a Feshbach resonance, we find that the conductivity spectrum broadens, as increased rates of collisions between the particles speed the decay of the induced currents. Our data is suggestive of a transport time that scales as $1/U^2$ for small $U$, consistent with a perturbative calculation based on Fermi's golden rule. However, the measured f-sum reveals that spectral weight is not lost: interactions merely redistribute conductivity among other frequencies in the optical conductivity spectrum. \\ ${}^{1}$R. Anderson \textit{et al}., arXiv:1712.09965 (2017).\\ ${}^{2}$Z. Wu, E. Taylor, and E. Zaremba, Europhys. Lett. \textbf{110}, 26002 (2015). [Preview Abstract] |
Tuesday, May 29, 2018 2:36PM - 2:48PM |
D09.00004: Non-Equilibrium Mass Transport in the 1D Fermi-Hubbard Model Sebastian Scherg, Thomas Kohlert, Henrik Lüschen, Pranjal Bordia, Jan Stolpp, Jacek Herbrych, Fabian Heidrich-Meisner, Ulrich Schneider, Monika Aidelsburger, Immanuel Bloch We experimentally and numerically investigate the sudden expansion of interacting Fermions in a homogeneous one-dimensional lattice. Focusing on initial states with more than half filling, we observe a phase separation of singlons (quickly expanding particles on singly occupied lattice sites) and doublons (slow particles on doubly occupied lattice sites). We discuss evidence of quantum distillation in the limit of large interactions, which occurs if singlons distill out of the doublon cloud, leading to a contraction of the doublon region in the center of the cloud. For initial states with less than half filling, we find a phase of singlons expanding nearly independently of the interaction strength, which is in stark contrast to the behavior of Bosons. We attribute the weak effect of interactions to a less efficient generation of dynamical doublons due to the Pauli principle and discuss the role of the integrability of the 1D Fermi-Hubbard model. [Preview Abstract] |
Tuesday, May 29, 2018 2:48PM - 3:00PM |
D09.00005: Probing the quench dynamics of antiferromagnetic correlations in a 2D quantum Ising spin system Elmer Guardado-Sanchez, Peter T. Brown, Debayan Mitra, Trithep Devakul, David A. Huse, Peter Schau\ss, Waseem S. Bakr Simulating the real-time evolution of quantum spin systems far out of equilibrium poses a major theoretical challenge, especially in more than one dimension. We experimentally explore quench dynamics in a two-dimensional Ising spin system with transverse and longitudinal fields. We realize the system with a near unit-occupancy atomic array of over 200 atoms obtained by loading a spin-polarized band insulator of fermionic lithium into an optical lattice and induce short-range interactions by direct excitation to a low-lying Rydberg state. Using site-resolved microscopy, we probe antiferromagnetic correlations in the system after a sudden quench from a paramagnetic state and compare our measurements to exact calculations in the regime where it is possible. We achieve many-body states with longer-range antiferromagnetic correlations by implementing a near-adiabatic quench of the longitudinal field and study the buildup of correlations as we vary the speed with which we change the field. [Preview Abstract] |
Tuesday, May 29, 2018 3:00PM - 3:12PM |
D09.00006: Abstract Withdrawn
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Tuesday, May 29, 2018 3:12PM - 3:24PM |
D09.00007: ABSTRACT WITHDRAWN |
Tuesday, May 29, 2018 3:24PM - 3:36PM |
D09.00008: A coherent perfect absorber for matter waves Christian Baals, Andreas M\"ullers, Bodhaditya Santra, Jian Jiang, Jens Benary, Ralf Labouvie, Dmitry A. Zezyulin, Vladimir V. Konotop, Herwig Ott Coherent perfect absorption (CPA), i.e. the complete extinction of bidirectional incoming radiation by a complex potential in a wave- guiding medium, is an effect that relies on the destructive interference of reflected and transmitted waves. It has been observed in many different linear systems like for example for light interacting with absorbing scatterers or for sound waves. Extending the concept of CPA to non-linear systems we find that the conditions for CPA can be achieved easier than in the linear case since localised absorption in a non-linear medium stabilises the system. We experimentally demonstrate CPA for matter waves with an atomic Bose-Einstein condensate in a one-dimensional optical lattice with an absorptive site where the absorption is introduced by an electron beam. [Preview Abstract] |
Tuesday, May 29, 2018 3:36PM - 3:48PM |
D09.00009: Measuring Optical Conductivity of Atoms in a Lattice Vijin Venu, Rhys Anderson, Fudong Wang, Peihang Xu, Stefan Trotzky, Frederic Chevy, Joseph H. Thywissen We discuss how to measure the global conductivity of ultracold atoms through center-of-mass dynamics [1]. The system under study is a quantum degenerate gas of fermionic potassium in a cubic optical lattice. We realize the proposal of Wu et al. [2], wherein a periodic force is applied to the cloud by dynamic displacement of the trapping beam. The steady state bulk current due to the periodic modulation is deduced from the center of mass position of the cloud, measured in-situ with high-resolution fluorescence imaging. A complex conductivity $\sigma(\omega)$ is measured as the ratio of particle current to the applied force as a function of the drive frequency $\omega$. The observed response differs from the Kohn response of a gas because of the presence of a lattice. The breaking of translational invariance manifests as a shift in the peak response, a loss of spectral weight and a broadening. Comparing the response to force applied along two in-plane axes, we determine both on-axis and off-axis conductivity, which allows a direct measure of the Hall conductivity.\\ $^1$R. Anderson \textit{et. al}., arXiv:1712.09965 (2017).\\ $^2$Z. Wu, E. Taylor, and E. Zaremba, Europhys. Lett. \textbf{110}, 26002 (2015). [Preview Abstract] |
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