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 U02: Long-range or Anisotropic Interactions in Cold Gases |
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Chair: Mingwu Lu, JQI, University of Maryland, College Park and National Institute of Standards and Technology Room: Grand A |
Friday, June 1, 2018 8:00AM - 8:12AM |
U02.00001: Droplet crystal ground states of a dipolar Bose gas P Blair Blakie, Danny Baillie We show that the ground state of a dipolar Bose gas in a cylindrically symmetric harmonic trap has a rich phase diagram, including droplet crystal states in which a set of droplets arrange into a lattice pattern that breaks the rotational symmetry. An analytic model for small droplet crystals is developed and used to obtain a zero temperature phase diagram that is numerically validated. We show that in certain regimes a coherent low-density halo surrounds the droplet crystal giving rise to a novel phase with localized and extended features. [Preview Abstract] |
Friday, June 1, 2018 8:12AM - 8:24AM |
U02.00002: Scissors mode of dipolar quantum droplets Tim Langen, Igor Ferrier-Barbut, Matthias Wenzel, Fabian Boettcher, Mathieu Isoard, Sandro Stringari, Tilman Pfau We report on the observation of the scissors mode of a single dipolar quantum droplet. The existence of this mode is due to the breaking of the rotational symmetry by the dipole-dipole interaction, which is fixed along an external homogeneous magnetic field. By modulating the orientation of this magnetic field, we introduce a new spectroscopic technique for studying dipolar quantum droplets. This provides a precise probe for interactions in the system allowing to extract a background scattering length for ${}^{164}$Dy of $69(4)\,a_0$. Our results establish an analogy between quantum droplets and atomic nuclei, where the existence of the scissors mode is also due only to internal interactions. They further open the possibility to explore physics beyond the available theoretical models for strongly-dipolar quantum gases. [Preview Abstract] |
Friday, June 1, 2018 8:24AM - 8:36AM |
U02.00003: Emergence of striped states in quantum ferrofluids Antun Balaz, Axel Pelster In the recent experiment [1], striped states in a many-body system of tilted dipoles were observed in a quantum ferrofluid of a strongly dipolar BEC of dysprosium, leading to a formation of atomic droplets. In Ref.~[2] it was demonstrated that the stability of such droplets is due to a quantum fluctuation correction of the ground-state energy [3, 4]. Here we extend this previous theoretical description and develop a full Bogoliubov-Popov theory, which also takes into account the condensate depletion due to quantum fluctuations. We apply our novel approach to study in detail the emergence of striped states and their properties. To this end we perform extensive numerical simulations and determine how the critical tilting angle depends on both the atom number and the trap geometry. Our investigations turn out to be relevant for extracting the yet unknown s-wave background scattering length of dysprosium from the experiments of Ref.~[1]. \newline [1] M. Wenzel, et al., Phys. Rev. A {\bf 96}, 053630 (2017).\newline [2] L. Chomaz, et al., Phys. Rev. X {\bf 6}, 041039 (2016).\newline [3] T. D. Lee, et al., Phys. Rev. {\bf 106}, 1135 (1957).\newline [4] A. R. P. Lima and A. Pelster, Phys. Rev. A {\bf 84}, 041604(R) (2011); Phys. Rev. A {\bf 86}, 063609 (2012). [Preview Abstract] |
Friday, June 1, 2018 8:36AM - 8:48AM |
U02.00004: Temperature dependent shape of self-bound dipolar droplets Mehmet Oktel, Enes Aybar Recently observed self-bound droplets of dipolar bosons display a novel form of equilibrium which is stabilized by fluctuations. We investigate the role of thermal fluctuations in addition to the quantum fluctuations in these systems and show that the equilibrium shape of the condensate is strongly affected even at low temperatures where the thermal depletion is of the order of zero temperature depletion and the condensate fraction remains high. As the temperature is raised from zero to $\sim g n_0/k_B$ the droplets become more prolate where $g n_0$ is the mean field short range interaction energy at the center of the droplets. The effect of temperature on the condensate shape can also be observed for stable $\epsilon_{dd}<1$ dipolar trapped gases for $\epsilon_{dd}$ close to one. [Preview Abstract] |
Friday, June 1, 2018 8:48AM - 9:00AM |
U02.00005: The effect of anisotropy of dipolar hopping on localization in three-dimensional lattices Joshua T Cantin, Tianrui Xu, Roman V Krems It has become widely accepted that particles with long-range hopping do not undergo Anderson localization. However, several recent studies demonstrated localization of particles with long-range hopping. In particular, it was recently shown that the effect of long-range hopping in 1D lattices can be mitigated by cooperative shielding, which makes the system behave effectively as one with short-range hopping. Here, we show that cooperative shielding, demonstrated previously for 1D lattices, extends to 3D lattices with \emph{isotropic} long-range $r^{-3}$ hopping, but not to 3D lattices with dipolar \emph{anisotropic} hopping. Since cooperative shielding enables localization, our results suggest (though do not prove) that localization in 3D lattices is possible for particles with isotropic long-range hopping, but not anisotropic long-range hopping. We show that the anisotropy of the dipolar long-range hopping qualitatively changes the energy level statistics, the scaling with the lattice size and the diffusion dynamics of wave packets in disordered 3D lattices. [Preview Abstract] |
Friday, June 1, 2018 9:00AM - 9:12AM |
U02.00006: Thermalization near integrability in a dipolar quantum Newton's cradle Wil Kao, Yijun Tang, Kuan-Yu Li, Sangwon Seo, Krishnanand Mallayya, Marcos Rigol, Sarang Gopalakrishnan, Benjamin Lev Isolated quantum many-body systems with integrable dynamics do not thermalize starting from generic initial states. As one perturbs such systems away from integrability, thermalization sets in, but the nature of the crossover from integrable to thermalizing behavior remains unclear. We investigate this problem by studying the dynamics of the momentum distribution in a dipolar quantum Newton's cradle consisting of highly magnetic dysprosium atoms -- the first one-dimensional Bose gas with strong, tuneable magnetic dipole-dipole interactions. We provide the first experimental evidence that thermalization close to integrability exhibits a fast dephasing followed by near-exponential thermalization, and the measured thermalization rate is consistent with a parameter-free theoretical estimate. By providing tunability between regimes of integrable and nonintegrable dynamics, our work sheds light on the temporal structure by which isolated quantum many-body systems approach thermalization. [Preview Abstract] |
Friday, June 1, 2018 9:12AM - 9:24AM |
U02.00007: Progress toward a dipolar quantum gas microscope with a reflective objective. Aaron Krahn, Greg Phelps, Anne Hebert, Sepehr Ebadi, Susannah Dickerson, Markus Greiner Dipolar atoms present an exciting opportunity to extend previous quantum gas microscope (QGM) experiments to more complex systems influenced by long range, anisotropic interactions. We present on current progress toward the construction of a QGM for ultracold Erbium atoms in an optical lattice, including the development of a novel imaging system for single-site resolution. While most QGMs until now have typically utilized a high numerical aperture microscope objective, we discuss a reflective mirror alternative that offers an equally high NA, a comparable field of view, and a larger working distance that keeps the atoms far from any surfaces. By operating in a Schmidt telescope configuration, this imaging system is well-suited both for collecting 401 nm imaging fluorescence and for the creation of an expandable lattice. [Preview Abstract] |
Friday, June 1, 2018 9:24AM - 9:36AM |
U02.00008: Quantum spinor gases of dipolar fermions. Lauriane Chomaz, Simon Baier, Daniel Petter, Alexander Patscheider, Jan Hendrick Becher, Gabriele Natale, Manfred Mark, Francesca Ferlaino Ultracold gases of highly magnetic atoms such as erbium offer an ideal platform for investigating novel aspects of many-body quantum phenomena in the presence of dipole-dipole interactions. We have realized and studied tunable~spin mixtures of~fermionic erbium 167. Our achievements rely on a lattice protection technics. In a first set of experiments, we explore the scattering properties of the two lowest spin states. We perform high resolution Feshbach spectroscopy and identify a comparatively broad interspin resonance in the vicinity of which, we precisely map the interspin scattering length as a function of the magnetic field via lattice modulation spectroscopy. This system paves the way for studying a broad range of physical phenomena from BEC-BCS crossover physics to lattice spin physics. In a second set of experiments, we prepare high-filling and pure samples of high spin states in a deep lattice and study the spin dynamics driven by off-site spin-changing dipolar interactions. A magnetization-conserving flip-flop dynamics shows a resonant behavior with the relative detuning of the neighboring spin states. We investigate the characteristic dependences of the dynamics on resonance, in particular with the spin state quantum number and with the quantization axis. [Preview Abstract] |
Friday, June 1, 2018 9:36AM - 9:48AM |
U02.00009: Many-body dipolar dynamics in 3D lattice clocks Chunlei Qu, Ana Maria Rey Alkaline-earth-metal atoms have recently attracted an intensive research interest in the cold-atom community as they can be used for the development of atomic clocks with unprecedented stability and accuracy. Typical 1D optical lattice clocks (OLCs) suffer from clock shifts induced by the atomic collisions and this has stimulated the built up of next-generation OLCs in a 3D lattice operating in the regime where there is at most one atom per site and thus the clock becomes immune to atomic collisions. In these 3D lattice clocks, however, atoms can still interact via long-range dipolar interactions which can impact the performance of the clock. At the same time, the state-of-the-art spectral sensitivity of these clocks can open a promising platform for studying dipolar many-body quantum physics. In this talk, we will present our systematical investigation of the role of both elastic and dissipative long-range interactions in clock interrogation. We will report the observation of intriguing dynamics and phases depending on the lattice geometry and dipole orientation. Our results not only will aid in the design of the future generation of ultra-precise atomic clocks but also illuminates the rich physics that emerges in driven-dissipative open quantum many-body systems. [Preview Abstract] |
Friday, June 1, 2018 9:48AM - 10:00AM |
U02.00010: Quantum paramagnetism in dipolar Heisenberg models Ahmet Keles, Erhai Zhao We present the theoretical phase diagrams for two dimensional spin one-half Heisenberg models with long range, anisotropic dipole-dipole interactions motivated by recent experiments on ultracold polar molecules in optical lattices. We consider localized dipolar molecules aligned along the direction of external electric field, and analyze the competing instabilities towards long range orders using non-perturbative functional renormalization group theory. We identify three long range ordered phases, the antiferromagnetic NĂ©el, the stripe and the spiral phases. Surprisingly, we also find a wide region of the parameter space where strong quantum fluctuations lead to paramagnetic behavior down to lowest numerical renormalization scales. Our findings provide further evidence that ultracold dipolar gases constitute a promising route to emulate frustrated quantum magnetism and search for quantum spin liquids. [Preview Abstract] |
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