Bulletin of the American Physical Society
51st Annual Meeting of the APS Division of Atomic, Molecular and Optical Physics
Volume 65, Number 4
Monday–Friday, June 1–5, 2020; Portland, Oregon
Session H08: Disordered SystemsLive

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Chair: Samir Bali, Miami University Room: Portland 255 
Wednesday, June 3, 2020 10:30AM  10:42AM Live 
H08.00001: Out of equilibrium dynamics of the disordered two dimensional Bose Hubbard model in the strong coupling regime Matthew Fitzpatrick, Malcolm Kennett, Ali MokhtariJazi We develop a strongcoupling approach for calculating spatiotemporal correlations in the disordered BoseHubbard model. We derive equations of motion for the disorderaveraged singleparticle Green's function, allowing us to study the relaxation dynamics from highly out of equilibrium initial conditions. We discuss how our formalism can be applied to the study of slow dynamics observed in recent experiments using cold atoms to simulate the two dimensional Bose Hubbard model. [Preview Abstract] 
Wednesday, June 3, 2020 10:42AM  10:54AM Live 
H08.00002: $\mathbb{Z}_2$ Characterization for ThreeDimensional Multiband Hubbard Models Bernhard Irsigler, JunHui Zheng, Fabian Grusdt, Walter Hofstetter We introduce three numerical methods for characterizing the topological phases of threedimensional multiband Hubbard models based on twisted boundary conditions, Wilson loops, as well as the local topological marker. We focus on the halffilled, threedimensional timereversalinvariant Hofstadter model with finite spinorbit coupling. Besides the weak and strong topological insulator phases we find a nodal line semimetal in the parameter regime between the two threedimensional topological insulator phases. Using dynamical meanfield theory combined with the topological Hamiltonian approach we find stabilization of these threedimensional topological states due to the Hubbard interaction. We study surface states which exhibit an asymmetry between left and right surface originating from the broken parity symmetry of the system. Our results set the stage for further research on inhomogeneous threedimensional topological systems, proximity effects, topological Mott insulators and nontrivially linked nodal line semimetals. [Preview Abstract] 
Wednesday, June 3, 2020 10:54AM  11:06AM Live 
H08.00003: Velocitysorting and stochastic resonances in a dissipative optical lattice Alexander Staron, Kefeng Jiang, Ajithamithra Dharmasiri, Anthony Rapp, Samir Bali We present detailed measurements of pumpprobe spectra which reveal evidence for a spontaneous emissionenabled Brownian ratchet capable of spatially sorting a selected velocity class of atoms in a dissipative optical lattice. We show that choosing different incident angles of the probe beam allows us to select different velocityclasses of atoms for directed transport. For the first time via direct pumpprobe spectroscopy, we explore the possibility of observing a classical stochastic resonance in an optical lattice, where environmental fluctuations in the form of random spontaneous emission recoils are resonantly coupled to the atomic intrawell oscillation frequency to yield enhanced ratcheting. We discuss prospects for observing a quantum stochastic resonance in cold atoms by inducing synchronization between a weak, driving frequency and the stochastic quantum tunneling rate between adjacent lattice wells. Funded by Army Research Office (ARO). [Preview Abstract] 
Wednesday, June 3, 2020 11:06AM  11:18AM Live 
H08.00004: Cloud shape of a molecular BoseEinstein condensate in a disordered trap: a case study of the dirty boson problem Milan Radonjic, Benjamin Nagler, Sian Barbosa, Jennifer Koch, Axel Pelster, Artur Widera We study, both experimentally and theoretically, the ground state static geometric properties of a harmonically trapped BoseEinstein condensate of lithium6 molecules in laser speckle potentials by determining the average transverse column density profiles and the corresponding cloud widths [1]. To this end, we use the cumulant expansion method [2] to develop a theory that is nonperturbative with respect to the disorder strength and includes quantum fluctuations. For small disorder strengths we find quantitative agreement with the perturbative approach of Huang and Meng [3]. For strong disorder our theory perfectly reproduces the geometric mean of the measured transverse widths. However, we also observe a systematic deviation of the individual measured widths from the theoretically predicted ones. Moreover, the measured cloud aspect ratio monotonously decreases with increasing disorder strength, while the theory yields a constant ratio. We discuss this discrepancy in light of more exact numerical simulations that support our theoretical findings. [1] B. Nagler et al., arXiv:1911.02626 [2] R. Kubo, J. Phys. Soc. Jpn. 17, 1100 (1962) [3] K. Huang and H. F. Meng, Phys. Rev. Lett. 69, 644 (1992) [Preview Abstract] 
Wednesday, June 3, 2020 11:18AM  11:30AM On Demand 
H08.00005: Controlling vortex lattice structure of binary BoseEinstein condensates via disorder induced vortex pinning. Bishwajyoti Dey We numerically simulate vortex lattice structures in rotating twocomponent BoseEinstein condensates in presence of impurities or disorder. Pinning of vortices by randomly distributed impurities leads to new structures of the vortex lattice. As the ratio of intercomponent to intracomponent couplings increases, the interlocked vortex lattice structure undergo phase transitions from triangular to square, doublecore lattices, and eventually develop “serpentine” vortex sheets. We show that even a single impurity pinning potential changes the vortex lattice structure from triangular to square. Accordingly, single or double impurities significantly change the structure of the vortex lattice in the overlap region having combination of triangular and square lattice. In presence of periodic pinning potential or optical lattice, the vortex lattice structure gets pinned to the optical lattice and acquire its structure. In presence of random pinning potential or disorder, the vortex lattice melts. The melting and loss of longrange order occurs with increasing rotational frequency through two steps. In the first step there is loss of positional order but orientational order is retained and in the second, both positional and orientational orders are lost. [Preview Abstract] 
Wednesday, June 3, 2020 11:30AM  11:42AM On Demand 
H08.00006: Disorderinduced transition in a HarperHofstadter system QiYu Liang, Dimitrios Trypogeorgos, Ana ValdésCuriel, Mingshu Zhao, Junheng Tao, Ian Spielman The HarperHofstadter model describes particles in twodimensional (2D) lattices subjected to a uniform magnetic field. Ultracold atomic gases in optical lattices are an ideal platform to study this model, thanks to their capability for realizing large and tunable magnetic fluxes per lattice plaquette. We experimentally assembled such a 2D lattice rolled into a long tube, just 3site around, thereby realizing periodic boundary conditions. These three sites were constructed from a synthetic dimension built from the atoms' internal degrees of freedom. We inserted an additional longitudinal flux through the long axis of the cylinder, a process which has no analogy in a planar geometry. We observed an unexpected disorderinduced transition. Counterintuitively, the dynamic evolution of the system is exquisitely phase sensitive without disorder, and the sensitivity can be suppressed by introducing disorder. This phenomenon can be understood in two ways: (1) a spatial selfaveraging effect and (2) interference between different matterwave momentum states. Future prospects include characterizing exotic phases and phase transitions and realizing topological fractional charge pumping in strongly correlated regimes. [Preview Abstract] 
Wednesday, June 3, 2020 11:42AM  11:54AM 
H08.00007: Complex network description of phase transitions in the classical and quantum disordered Ising Model Mina Fasihi, Haley Cole, Lincoln Carr, Guillermo Garcia Perez, Sabrina Maniscalco Complex~network analysis is a powerful tool to describe and characterize classical systems such as~the~Ising model in a transverse magnetic field. Measuring spinspin correlations gives~rise to the adjacency matrix, representing a weighted network. In this study, the spinspin correlations at different temperatures~are~analytically calculated, yielding~phasedependent~complex~networks,~from simple networks in the low temperature ferromagnetic limit to random ones at high temperature.~ The network structure varies as the transverse field and temperature~change,~recovering the phase diagram and providing initial insight into correlations in the critical region.~Analyzing the resulting complex network using a variety of network measures such as the degree histogram, average clustering, betweenness centrality and the graph entropy, the complexity is characterized.~ This method is applied for both the disordered classical Ising and quantum Ising lattice, demonstrating the role of finite temperature and disorder in generation of complexity. [Preview Abstract] 
Wednesday, June 3, 2020 11:54AM  12:06PM 
H08.00008: Logarithmic entanglement growth in twodimensional disordered fermionic systems Jesko Sirker, Yang Zhao We investigate the growth of the entanglement entropy $S_{\textrm{ent}}$ following global quenches in twodimensional free fermion models with potential and bond disorder. For the potential disorder case, we show that an intermediate weak localization regime exists in which $S_{\textrm{ent}}(t)$ grows logarithmically in time $t$ before Anderson localization sets in. For the case of binary bond disorder near the percolation transition, we find additive logarithmic corrections to area and volume laws as well as a scaling at long times, which is consistent with an infinite randomness fixed point. [Preview Abstract] 
Wednesday, June 3, 2020 12:06PM  12:18PM Not Participating 
H08.00009: Fluctuation theorems and an arrow of time for weak spin measurements of an ultracold gas Maitreyi Jayaseelan, Sreenath K. Manikandan, Andrew N. Jordan, Nicholas P. Bigelow When a quantum system undergoes not projective but weak measurements, the dynamics followed by the system are in general symmetric under timereversal. Yet, as the quantum system is monitored and information about its state is obtained, the quantum mechanical wavefunction is seen to undergo irreversible collapse to one of the eigenstates of the observable being measured. Fluctuation theorems quantify the emergence of irreversibility from microscopically reversible dynamics such as when quantum systems are weakly measured. Here we show the emergence of irreversibility in weak measurements of spin state performed on an ultracold atomic cloud. A coherent twophoton Raman process prepares the atoms in a superposition of spin states in a pseudospin$1/2$ system. A timeofflight SternGerlach process with variable strength subsequently correlates atomic spin state (our observable) with spatial position (our readout). The spatial distribution of the coherent atomic cloud thus serves to provide an ensemble average of weak spin measurements on the cloud in a single shot. We demonstrate the existence of a strictly positive average arrow of time that emerges as our measurement strength is varied, and we characterise the irreversibility of such spinstate measurements in our system. [Preview Abstract] 
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