Bulletin of the American Physical Society
APS March Meeting 2017
Volume 62, Number 4
Monday–Friday, March 13–17, 2017; New Orleans, Louisiana
Session X27: Dipolar Interactions in Ultracold GasesFocus

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Sponsoring Units: DAMOP Chair: Rick Mukherjee, Rice University Room: 290 
Friday, March 17, 2017 8:00AM  8:36AM 
X27.00001: Extended BoseHubbard models with ultracold magnetic atoms. Invited Speaker: Francesca Ferlaino 
Friday, March 17, 2017 8:36AM  8:48AM 
X27.00002: Pairing superfluidty in a Weyl semimetal with dipolar interaction Long Zhang, XiongJun Liu We study the topological superfluid phase of a threedimensional Weyl semimetal realized in a singlecomponent dipolar Fermi gas. The system is constructed by employing both the nearest and secondnearest hopping, and generating periodic gauge potentials in an anisotropic cubic lattice. By calculating the superfluid pairing induced by dipoledipole interaction, we determine the phase diagram of this system and obtained many novel properties. [Preview Abstract] 
Friday, March 17, 2017 8:48AM  9:00AM 
X27.00003: Dipolar lattice bosons in the presence of longrange hopping Chao Zhang, Arghavan SafaviNaini, Barbara CapogrossoSansone We report on numerical results based on quantum Monte Carlo simulations of a system of twodimensional hardcore lattice bosons in the presence of longrange hopping and longrange twobody interactions resulting from dipoledipole interactions. This is equivalent to the XXZ model in the presence of dipolar interactions which can be realized by a lattice gas of polar molecules, creating a flexible platform for the study of quantum magnetism. The system features three phases: a superfluid, a supersolid, and a checkerboard solid. Next we mimic the current experimental conditions, that is a lattice of polar molecules away from unit filling, by adding static disorder. Under these conditions we study the localization of particles and the stabilization of a disorderinduced insulating phase. [Preview Abstract] 
Friday, March 17, 2017 9:00AM  9:12AM 
X27.00004: Developments in driving atomic transitions using the ponderomotive interaction Kaitlin Moore, Georg Raithel We describe recent developments in a novel spectroscopic method that couples Rydberg states using an intensitymodulated optical lattice. The method is fundamentally different from traditional microwave spectroscopy: it engages the $\mathbf{A} \cdot \mathbf{A}$ (ponderomotive) term rather than the $\mathbf{A} \cdot \mathbf{p}$ term of the atomfield interaction Hamiltonian. The method allows us to drive GHzfrequency transitions between Rydberg states with optical spatial resolution and is not subject to the usual electricdipole selection rules (i.e., higherorder multipole transitions are driven in firstorder timedependent perturbation)\footnote{K.R. Moore, S.E. Anderson, and G. Raithel, \textbf{Nat. Comm.} 6, 6090 (2015)},\footnote{K.R. Moore and G. Raithel, \textbf{Phys. Rev. Lett.}, 115, 163003 (2015)},\footnote{B. Knuffman and G. Raithel, \textbf{Phys. Rev. A}, 75, 053401, (2007)}. We review our previous experimental results using cold atoms, including an extension of this method into the nearsubTHz regime via modulation harmonics. We present new theoretical results showing extensions of this method to oddparity transitions. Finally, we discuss the proposed application of this method to a precision measurement of the Rydberg constant using circularstate Rydberg atoms. [Preview Abstract] 
Friday, March 17, 2017 9:12AM  9:24AM 
X27.00005: Heat Transfer Through Dipolar Coupling: Sympathetic cooling without contact Mehmet Oktel, Basak Renklioglu, Bilal Tanatar We consider two parallel layers of dipolar ultracold gases at different temperatures and calculate the heat transfer through dipolar coupling. As the simplest model we consider a system in which both of the layers contain twodimensional spinpolarized Fermi gases. The effective interactions describing the correlation effects and screening between the dipoles are obtained by the EulerLagrange Fermihypernettedchain approximation in a single layer. We use the randomphase approximation (RPA) for the interactions across the layers. We find that heat transfer through dipolar coupling becomes efficient when the layer separation is comparable to dipolar interaction length scale. We characterize the heat transfer by calculating the time constant for temperature equilibration between the layers and find that for the typical experimental parameter regime of dipolar molecules this is on the order of milliseconds. We generalize the initial model to BosonBoson and FermionBoson layers and suggest that contactless sympathetic cooling may be used for ultracold dipolar molecules. [Preview Abstract] 
Friday, March 17, 2017 9:24AM  9:36AM 
X27.00006: Finite Temperature RPA Calculations of 2D Dipolar Bosons at Arbitrary Tilt Angles Pengtao Shen, Khandker Quader We present finiteT Random Phase Approximation (RPA) calculations on a system of 2D dipolar bosons, with dipoles oriented at an angle to the direction perpendicular to the confining 2D plane. Our calculations are done over a wide range of density, temperature, and dipolar strength, for various dipolar tilt angles. For a given temperature, we find the system to be in a quasicondensate phase, which undergoes a collapse transition at large tilt angles, and a finite momentum instability, signaling a striped phase, at sufficiently large values of dipolar coupling strength. Within RPA, we also consider the effect of additional repulsive and attractive contact interactions. Finally, we explore the effect of a trap on the 2D system. We construct phase diagrams depicting the phases and instabilities. We discuss how our results may apply to ultracold dense Bose gas of polar molecules, such as $^{41}$K$^{87}$Rb, that has been realized experimentally. [Preview Abstract] 
Friday, March 17, 2017 9:36AM  9:48AM 
X27.00007: Dynamics of correlations in longrange quantum systems follwing a quantum quench Lorenzo Cevolani, Giuseppe Carleo, Laurent SanchezPalencia We study how and how fast correlations can spread in a quantum system abruptly driven out of equilibrium by a quantum quench. This protocol can be experimentally realized and it allow to address fundamental questions concerning the quasilocality principle in isolated quantum systems with both short and longrange interactions. We focus on two different models describing, respectively, lattice bosons, and spins. Our study is based on a combined approach, based on one hand on accurate manybody numerical calculations and on the other hand on a quasiparticle microscopic theory. We find that, for sufficiently fast decaying interaction potential the propagation is ballistic and the LiebRobinson bounds for longrange interactions are never attained. When the interactions are really longrange, the scenario is completely different in the two cases. In the bosonic system the locality is preserved and a ballistic propagation is still present while in the spin system an instantaneous propagation of correlations completely destroys locality. Using the microscopic point of view we can quantitatively describe all the different regimes, from instantaneous to ballistic, found in the spin model and we explain how locality is protected in the bosonic model leading to a ballistic propagation. [Preview Abstract] 
Friday, March 17, 2017 9:48AM  10:00AM 
X27.00008: Assessing approximations to spin dynamics using a geometric representation of spin correlations Rick Mukherjee, Kenneth Wang, Tony Mirasola, Kaden Hazzard We have developed a geometric way to visualize spin correlations, including their dynamical evolution. Phenomena that look complicated and mysterious when analyzed by the components of their correlations become simple and intuitive when described geometrically. We will describe how this geometric representation provides insight into the accuracy of various approximations to the dynamics, such as truncated Wigner approximations. [Preview Abstract] 
Friday, March 17, 2017 10:00AM  10:12AM 
X27.00009: Geometric interpretation of spin correlations and applications to ultracold physics Tony Mirasola, Kenneth Wang, Ian G. White, Jacob Hollingsworth, Rick Mukherjee, Kaden R.A. Hazzard Abstract: We develop a general method to visualize spin correlations and demonstrate its broad usefulness for different models realized in ultracold matter, from fermions in lattices to trapped ions and ultracold molecules. We provide a onetoone map between the spin correlations and certain threedimensional objects, analogous to the map between single spins and Bloch vectors. This makes the geometric structure of the correlations manifest. Moreover, much as one can reason geometrically about dynamics using a Bloch vector  e.g. a magnetic field causes it to precess and dephasing causes it to shrink  we show that analogous reasoning holds for our visualization of correlations for real physical spin models. Applying this to ultracold matter, we find that seemingly mysterious and complicated dynamics becomes straightforward to understand in this representation. [Preview Abstract] 
(Author Not Attending)

X27.00010: Enhanced fractal dynamics of a BEC induced by dipolar interactions Jessica Taylor, Boaz Ilan, Kevin Mitchell The escape dynamics of a BoseEinstein condensate (BEC) from a potential well are studied computationally. Previous studies based on the Nonlinear Schr\"{o}dinger / GrossPitaevskii (NLSGP) equation have predicted the fractal nature of the escaping flux. In attractive BECs (focusing NLS), the wave packet can undergo collapse. The effects of dipolar interactions suppress this collapse while also mitigating the wave packet's dispersion, resulting in enhanced fractal dynamics. This is joint work with Boaz Ilan and Kevin Mitchell. [Preview Abstract] 
Friday, March 17, 2017 10:24AM  10:36AM 
X27.00011: Casimir forces between two impurities in a lattice Andrei Pavlov, Dmitri Efremov, Jeroen van den Brink One of the fundamental properties of matter is the Casimir force, i.e. interaction of classical objects via quantum fluctuations. It appears in various field, including optics, Bosecondensates, microstructure geometry compounds, etc. The usual wisdom is that the Casimir force between two atoms decays as $r^{(2D+1)}$, which is originated from the two boson exchange in the lowest order of the perturbation theory. Stimulated by the recent experiments on the high temperature superconductor H$_3$S under high pressure, we reconsider the Casimir forces between two impurities in solid state physics via virtual phonons at long and short distances. We found strong deviation from the standard law at short distances which depends on the masses of impurities atoms. At long distances it comes to the standard $r$dependence, but the value of the prefactor is much larger than it's expected from the lowest orders of the perturbation theory. These differences become important when the impurity masses differ from the lattice atoms more than twice. Finally we apply our results to impurity atoms of deuterium and tritium in H$_3$S. [Preview Abstract] 
Friday, March 17, 2017 10:36AM  10:48AM 
X27.00012: Spectroscopic Probe of the van der Waals Interaction between Polar Molecules and a Curved Surface Thorsten Emig, Giuseppe Bimonte, Robert Jaffe, Mehran Kardar Fluctuation induced interactions become most prominent in close to proximity to surfaces. Examples include van der Waals and Casimir forces. In this talk, we consider the shift of rotational levels of a diatomic polar molecule due to its van der Waals (vdW) interaction with a gently curved dielectric surface at submicron separations. The molecule is assumed to be in its electronic and vibrational ground state, and the rotational degrees are described by a rigid rotor model. We show that under these conditions retardation effects and surface dispersion can be neglected. The level shifts are found to be independent of temperature, and given by the quantum state averaged classical electrostatic interaction of the dipole with its image on the surface. We argue that the curvature induced line splitting is experimentally observable, and not obscured by natural line widths and thermal broadening. [Preview Abstract] 
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