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 K02: Elementary Excitations of Degenerate Gases |
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Chair: Gretchen Campbell, National Institute of Standards and Technology Room: Grand A |
Wednesday, May 30, 2018 2:00PM - 2:12PM |
K02.00001: Critical velocity for vortex shedding in a Fermi superfluid Bumsuk Ko, Jee Woo Park, Yong-il Shin The defining character of a superfluid is the existence of a critical velocity, below which a superfluid can flow through obstacles without dissipation. According to the Landau criterion, for a strongly interacting Fermi superfluid in the BEC-BCS crossover, the critical velocity is determined by the interplay between phonon and pair breaking excitations. Here, we explore the critical velocity for vortex dipole excitations in a strongly interacting Fermi superfluid of $^6$Li. This is done by translating a repulsive optical obstacle through the condensate and directly imaging the vortices after time of flight. The critical velocity is examined for a range of interaction parameters 1/$k_F a$ and obstacle travel distances $L$. In the two limits of $L$, we observe markedly different behaviors of the critical velocity: for short $L$, it shows a pronounced peak near unitarity, whereas for long $L$, the peak is strongly suppressed, implying that the onset of drag force occurs at a lower velocity and that the increase of the drag force with velocity is slow near unitarity. Further comparison of the measured critical velocity to the speed of sound and the pair breaking velocity, and the application of the periodic shedding model to determine the onset of the drag force will be discussed. [Preview Abstract] |
Wednesday, May 30, 2018 2:12PM - 2:24PM |
K02.00002: Abstract Withdrawn
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Wednesday, May 30, 2018 2:24PM - 2:36PM |
K02.00003: Experimental Investigation of Three-Component Solitons in F = 1 Bose-Einstein Condensates Thomas Bersano, Vandna Gokhroo, Peter Engels Dilute-Gas Bose-Einstein condensates are an exceptionally versatile test bed for the investigation of novel solitonic structures. While matter-wave solitons in one- and two-component systems have been the focus of intense research efforts, here we provide an extension to three-component systems. We demonstrate the existence of robust dark-bright-bright (DBB) and dark-dark-bright solitons in a multicomponent $F=1$ condensate. We observe lifetimes on the order of hundreds of milliseconds for these structures. Our experimental findings are corroborated by direct numerical simulations highlighting the persistence of, e.g., the DBB solitons states, as well as their robust oscillation in the trap. [Preview Abstract] |
Wednesday, May 30, 2018 2:36PM - 2:48PM |
K02.00004: Detecting Entrainment in Fermi-Bose mixtures. Khalid Hossain, Subhadeep Gupta, Michael Forbes The defining property of superfluids is that they flow without resistance. Entrainment -- where one superfluid drags along another as it flows -- may thus seem counter-intuitive, yet it is perfectly consistent with the Galilean covariance and absence of dissipation in superfluid mixtures, and may play a critical role in neutron stars where proton and neutron entrainment may underlie the puzzeling occurance of pulsar glitches. Although predicted by Andreev and Bashkin in 1975 for superfluid $^{3}$He and $^{4}$He mixtures, entrainment remains to be detected experimentally in cold atomic gases since it is a small effect, appearing at second order in the inter-particle interaction. In this talk I shall present an experimental proposal for detecting entrainment in $^{6}$Li-$^{174}$Yb Fermi-Bose mixture, taking advantage of the large mass ratio and carefully suppressing mean-field effects. [Preview Abstract] |
Wednesday, May 30, 2018 2:48PM - 3:00PM |
K02.00005: Designer Spatial Control of Interactions in Ultracold Gases Nithya Arunkumar, Arunkumar Jagannathan, John Thomas Optical control of scattering interactions can achieve high-resolution spatial and ultrafast temporal control of interactions in ultracold gases. We report on experiments that uses electromagnetically induced transparency near the energy-dependent narrow Feshbach resonance in $^6$Li Fermi gas to tune the interactions by 12 background scattering lengths. We achieve this tunability by changing the frequency of the laser light by merely a few MHz, thereby not altering the effective potential experienced by the atoms. By measuring mean field shifts from radio frequency spectra, we show that our method achieves the same level of tunability as magnetically tuning the scattering length. We further illustrate the versatility of our technique by creating spatially dependent interactions, where the central interacting region of the atomic cloud is ``sandwiched" between two weakly interacting regions or vice versa. [Preview Abstract] |
Wednesday, May 30, 2018 3:00PM - 3:12PM |
K02.00006: Yang monopoles and emergent three-dimensional topological defects in interacting bosons Yangqian Yan, Qi Zhou Yang monopole as a zero-dimensional topological defect has been well established in multiple fields in physics. However, it remains an intriguing question to understand interaction effects on Yang monopoles. Here, we show that collective motions of many interacting bosons give rise to exotic topological defects that are distinct from Yang monopoles seen by a single particle. Whereas interactions may distribute Yang monopoles in the parameter space or glue them to a single giant one of multiple charges, three-dimensional topological defects also arise from continuous manifolds of degenerate many-body eigenstates. Their projections in lower dimensions lead to knotted nodal lines and nodal rings. Our results suggest that ultracold bosonic atoms can be used to create emergent topological defects and directly measure topological invariant that are not easy to access in solids. [Preview Abstract] |
Wednesday, May 30, 2018 3:12PM - 3:24PM |
K02.00007: Atom Pairing in Optical Superlattices Jayampathi Kangara, Chingyun Cheng, Saeed Pegahan, Ilya Arakelyan, John Thomas We study the pairing of fermions in a one-dimensional optical superlattice of double-well potentials with tunable asymmetry. Radio frequency spectroscopy reveals the coexistence of two types of atom pairs with different symmetries for their center of mass wave functions. Our measurements are in excellent quantitative agreement with a multi-band model of the spectra, comprising hundreds of discrete transitions, with symmetry-dependent initial state populations and transition strengths. Our work provides an understanding of the elementary pairing states in a superlattice, paving the way for new studies of strongly interacting many-body systems. [Preview Abstract] |
Wednesday, May 30, 2018 3:24PM - 3:36PM |
K02.00008: Topology, edge states, and zero-energy states of ultracold fermionic atoms in 1D optical superlattices Chih-Chun Chien, Yan He, Kevin Wright, Said Kouachi Recent advance in generating optical superlattices offers opportunities for exploring interesting band structures. The simplest, dimerized superlattice is known to be a topological insulator when modeled as the Su-Schrieffer-Heeger model. By generalizing the modulation of onsite potential and hopping coefficient to higher periods, more topological and geometrical properties can emerge in superlattices. We show that a 1D optical superlattice with modulating onsite potentials can have nonzero Chern numbers, and the bulk-boundary correspondence leads to localized edge states. We show possibilities of assembling two superlattices with different topologies into a ring, and two internal boundaries with localized edge states can be generated. In the presence of modulating hopping coefficients, there are symmetry-related modes showing localization or zero-energy. Selected schemes for measuring those special states by depleting the mobile particles away from the boundary or probing the local density of states will also be discussed. Reference: Y. He, K. Wright, S. Kouachi, and C. C. Chien, arXiv: 1712.06538. [Preview Abstract] |
Wednesday, May 30, 2018 3:36PM - 3:48PM |
K02.00009: Abstract Withdrawn
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Wednesday, May 30, 2018 3:48PM - 4:00PM |
K02.00010: Probing spin charge separation with ultracold atoms Xiwen Guan, Feng He The spin charge separation is the hall mark of the low energy physics in one dimension (1D). However, such a unique 1D phenomenon still lacks a comprehensive understanding in experiment. In this talk, we will discuss this novel quantum separation with quantum criticality of ultracold atoms. We will show that two-component ultracold Fermi and Bose gases exhibit different spin charge separation mechanisms. The former can form two Luttinger liquids (LLs) with different propogation velocities in charge and spin degrees of freedom. Whereas, the latter gives rise to the separation of a single LL from the bound states of spin waves. Such differences result in significantly different quantum power law scalings in magnetic and thermal properties. Measures of the speeds of the sounds, quantum scalings, magnetic orderings and the LLs with the criticality would provide a confirmative determination of the quantum separation at a many-body level. [Preview Abstract] |
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