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 H04: FOCUS: Quantum gases with long range interactions |
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Chair: Hossein Sadeghpour, Harvard Room: Wisconsin Center 102AB |
Wednesday, May 29, 2019 8:00AM - 8:30AM |
H04.00001: Controlling Quantum Spin Dynamics with Light Invited Speaker: Monika Schleier-Smith Coupling many atoms to a single mode of light provides an efficient means of generating quantum correlations in an extended many-body system. I will report on experiments in which we harness photons in an optical cavity to mediate “flip-flop” interactions among distant spins in a millimeter-long cloud of atoms, as we directly observe by real-space imaging of quench dynamics. In our spin-1 system, the exchange interaction enables correlated pair creation in the $m = \pm 1$ Zeeman states, a process analogous to spontaneous parametric down-conversion or to collisional spin mixing in Bose-Einstein condensates. In contrast to direct collisional interactions, non-local light-mediated interactions offer unprecedented opportunities for engineering the spatial structure of spin-spin couplings and correlations. I will describe progress and prospects in tailoring atom-light interactions to enable new directions in quantum simulation and to generate new resources for quantum-enhanced sensing. [Preview Abstract] |
Wednesday, May 29, 2019 8:30AM - 9:00AM |
H04.00002: The quantum phases of ultracold dipolar gases near a Roton excitation Invited Speaker: Francesca Ferlaino Discovered in liquid helium about 80 years ago, superfluidity is a counterintuitive phenomenon, in which quantum physics and particle-wave duality manifest at the macroscopic level. Since then, it has yielded many advances in understanding quantum matter, yet leaving mysterious some of its features. A hallmark of superfluidity is the existence of so-called “quasi-particles”, i.e. elementary excitations dressed by interactions. Laudau predicted two type of quasi-particles, the first ones being the well-known phonon mode. The second ones, much more bizarre and intriguing, are massive quasi-particles named rotons. They have large momenta, and, contrarily to ordinary (quasi)particles with energy increasing with the momentum, the roton dispersion relation exhibits a minimum at a finite momentum. This unusual behavior expresses the tendency of the fluids to build up short-wavelength density modulation in space, precursor of a crystallization instability and eventually to the elusive and highly-debated supersolid quantum phase. In 2003, theoreticians suggested that a similar rotonic excitation might also occur in dipolar Bose- Einstein condensates because of the special properties of the long-rang and anisotropic dipole- dipole interaction. We here report on the observation of roton quasiparticles in a dipolar gas of high magnetic Er atoms and first studies, demonstrating hallmarks of long-lived supersolid behavior, using a Bose-Einstein condensate of Dy atoms. [Preview Abstract] |
Wednesday, May 29, 2019 9:00AM - 9:12AM |
H04.00003: Excitations of a vortex line in an elongated dipolar condensate P. Blair Blakie, Au-Chen Lee, Danny Baillie, Russell Bisset We characterize the properties of a vortex line in an elongated dipolar Bose–Einstein condensate. Increasing the strength of the dipole-dipole interactions (DDIs) relative to the short-ranged contact interactions we find that the system crosses over to a self-bound vortex droplet stabilized from collapse by quantum fluctuations. We calculate the quasiparticle excitation spectrum of the vortex state, which is important in characterizing the vortex response and assessing its stability. When the DDIs are sufficiently strong we find that the vortex is dynamically unstable to quadrupolar modes. [Preview Abstract] |
Wednesday, May 29, 2019 9:12AM - 9:24AM |
H04.00004: Disorderless localization of polar gases in one-dimensional lattice Arya Dhar, Wei-Han Li, Xiaolong Deng, Luca Barbiero, Luis Santos One-dimensional polar gases in deep optical lattices present a severely constrained dynamics due to the interplay between dipolar interactions, energy conservation, and finite bandwidth. The appearance of dynamically-bound nearest-neighbor dimers results, due to the surprisingly relevant role of the $1/r^3$ tail of the dipolar interactions, in localization via dimer clusterization for very low densities, even for moderate dipole strengths. Furthermore, even weak dipoles, allow for self-bound superfluid or metallic lattice droplets with a finite doping of mobile, but confined, holons. Our results, which can be extrapolated to other power-law interactions, are directly relevant for current and future lattice experiments with magnetic atoms and polar molecules. [Preview Abstract] |
Wednesday, May 29, 2019 9:24AM - 9:36AM |
H04.00005: Stability diagrams and dynamics of quantum degenerate Fermi gases of polar molecules Antun Balaz, Vladimir Veljic, Axel Pelster A recent experimental realization of ultracold quantum degenerate gas of $^{40}$K$^{87}$Rb molecules opens up a new chapter in exploring strongly dipolar Fermi gases and many-body phenomena arising in that regime. This includes the deformation of the Fermi surface for polarized systems, where the electric dipoles have a preferential orientation, which can be achieved using an external field. Compared to atomic magnetic species, this effect will be significantly increased in ultracold gases of polar molecules, and the stability of the system is expected to strongly depend on its geometry. Using a mean-field variational approach based on the Wigner function, we show here that the stability of dipolar fermions depends only on the trap aspect ratios and orientation of the dipoles, thus exhibiting a universal behavior. We calculate the stability diagrams and the Fermi surface deformation, which is experimentally probed by time-of-flight expansions. Furthermore, we demonstrate how to take into account the dipole-dipole interaction in the system dynamics and that nonballistic effects during the time-of-flight expansion have to be considered for polar molecules. Our results are important for designing future experiments with dipolar fermions and for interpreting measurement data. [Preview Abstract] |
Wednesday, May 29, 2019 9:36AM - 9:48AM |
H04.00006: Phase diagram of lattice bosons with cavity-mediated long-range interactions with uncorrelated disorder Chao Zhang, Heiko Rieger Recent experiments with ultra-cold atoms in an optical lattice have realized cavity-mediated global range and observed the emergence of a supersolid and a density wave phase in addition to Mott insulator and superfluid phases. Here we consider theoretically the effect of uncorrelated disorder on the phase diagram of this system and study the two-dimensional Bose-Hubbard model with global range interactions and uncorrelated diagonal disorder. With the help of quantum Monte Carlo simulations using the Worm algorithm we determine the phase diagram of this model. We show that two kinds of Bose glass phases exist: one with and one without density wave order and discuss the nature of the various phase transitions that occur. [Preview Abstract] |
Wednesday, May 29, 2019 9:48AM - 10:00AM |
H04.00007: Scattering from the dark and adversarial modes: new self-organisation phases Davide Dreon, Andrea Morales, Philip Zupancic, Xiangliang Li, Alexander Baumgärtner, Tilman Esslinger, Tobias Donner A Bose-Einstein Condensate (BEC) inside an optical resonator can undergo a phase transition to a self-organised state when illuminated with a red-detuned pump beam. In our recent experiment, we study the interaction of the BEC with two non-degenerate polarisation modes of a cavity. I will show how the couplings to the two modes, which are independently tuned via the scalar and the vectorial part of the atomic polarisability, give rise to competing self-organisation phases. In a second experiment, we explore the blue side of the atomic resonance. We observe that self-organisation is still possible despite the atoms being expelled from the light fields, suppressing photon scattering. Moreover, the repulsive lattices induce non-trivial modifications of the band structure and the dispersive shift triggers dynamics of the order parameter, both effects leading to richer phase diagrams. [Preview Abstract] |
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