Bulletin of the American Physical Society
47th Annual Meeting of the APS Division of Atomic, Molecular and Optical Physics
Volume 61, Number 8
Monday–Friday, May 23–27, 2016; Providence, Rhode Island
Session M9: Novel Phases and Ordering in Fermi Gases 
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Chair: Ben Lev, Stanford University Room: 556AB 
Thursday, May 26, 2016 8:00AM  8:12AM 
M9.00001: Detecting $\pi$phase superfluids with $p$wave symmetry in a quasi1D optical lattice Bo Liu, Xiaopeng Li, Randall G. Hulet, W. Vincent Liu We propose an experimental protocol to create a $p$wave superfluid in a spinpolarized cold Fermi gas tuned by an $s$wave Feshbach resonance. A crucial ingredient is to add an anisotropic 3D optical lattice and tune the fillings of two spins to the $s$ and $p$ band, respectively. The pairing order parameter is confirmed to inherit $p$wave symmetry in its centerofmass motion. We find that it can further develop into a state of unexpected $\pi$phase modulation in a broad parameter regime. Experimental signatures are predicted in the momentum distributions, density of states and spatial densities for a realistic experimental setup. The $\pi$phase $p$wave superfluid is reminiscent of the $\pi$state in superconductorferromagnet heterostructures but differs in symmetry and physical origin. The spatiallyvarying phases of the superfluid gap provide a novel approach to synthetic magnetic fields for neutral atoms. It would represent another example of $p$wave pairing, first discovered in He3 liquids. [Preview Abstract] 
Thursday, May 26, 2016 8:12AM  8:24AM 
M9.00002: Experimental realization of the ionic Hubbard model on a honeycomb lattice with ultracold fermions R\'emi Desbuquois, Michael Messer, Thomas Uehlinger, Gregor Jotzu, Frederik G\"org, Daniel Greif, Sebastian Huber, Tilman Esslinger Ultracold atoms in optical lattices constitute a tool of choice to realize the FermiHubbard model. There, the onsite interaction energy opens a gap in the charge excitation spectrum, leading to a Mott insulating ground state. However, in the ionic Hubbard model, the addition of a staggered energy offset on each lattice site also leads to an insulating ground state with chargedensitywave ordering, even in the absence of interparticle interactions. In our experiment we realize the Ionic Hubbard model on a honeycomb lattice by loading a twocomponent interacting Fermi gas into an optical lattice with a staggered energy offset on alternating sites. The underlying density order of the ground state is revealed through the correlations in the noise of the measured momentum distribution. For a large energy offset, we observe a charge densitywave ordering, which is suppressed as the onsite interactions are increased. To further elucidate the nature of the ground state, we measure the double occupancy of lattice sites and the charge excitation spectrum for a wide range of parameters. [Preview Abstract] 
Thursday, May 26, 2016 8:24AM  8:36AM 
M9.00003: A longlived spinorbitcoupled dipolar Fermi gas Yijun Tang, Nathaniel Burdick, Wil Kao, Benjamin Lev We report on the demonstration of spinorbit coupling in a quantum degenerate dipolar Fermi gas of dysprosium. The $T/T_F = 0.4$ gas has a lifetime as large as 0.4 s under Raman dressing at densities exceeding $10^{13}$ cm$^{3}$. The lifetime is limited not by spontaneous emission but by dipolar relaxation loss, and the effect of the dipolar interaction is also observed in the dephasing of Rabi oscillations. This spinorbitcoupled dipolar gas will allow future studies of fermionic systems in the presence of synthetic gauge fields wherein long lifetimes are essential to observing collective effects. [Preview Abstract] 
Thursday, May 26, 2016 8:36AM  8:48AM 
M9.00004: A continuum of compass spin models on the honeycomb lattice Haiyuan Zou, Bo Liu, Erhai Zhao, W. Vincent Liu Quantum spin models with spatially dependent interactions, known as compass models, play an important role in the study of frustrated quantum magnetism. One example is the Kitaev model on the honeycomb lattice with spinliquid ground states. Another example is the geometrically frustrated quantum $120^\circ$ model whose ground state has not been unambiguously established. To generalize the Kitaev model beyond the exactly solvable limit and connect it with other models, we propose a new model, dubbed ``the tripod model," which contains a continuum of compasstype models. It not only unifies paradigmatic spin models, but also enables the study of their quantum phase transitions. We obtain the phase diagram of the tripod model numerically by tensor networks in the thermodynamic limit. We show that the ground state of the quantum $120^\circ$ model has longrange dimer order. Moreover, we find an extended spindisordered (spinliquid) phase between the dimer phase and an antiferromagnetic phase. The unification and solution of a continuum of frustrated spin models as outline here may be useful to exploring new domains of other quantum spin or orbital models. [Preview Abstract] 
Thursday, May 26, 2016 8:48AM  9:00AM 
M9.00005: Exotic topological density waves in cold atomic Rydberg fermions Xiaopeng Li Versatile controllability of interactions in ultracold atomic and molecular gases has now reached an era where quantum correlations and unconventional manybody phases can be studied with no corresponding analogues in solidstate systems. Recent experiments in Rydberg atomic gases have achieved exquisite control over nonlocal interactions, allowing novel quantum phases unreachable with the usual local interactions in atomic systems. Here I will discuss Rydbergdressed atomic fermions in a threedimensional optical lattice where we predict the existence of hitherto unheardof exotic mixed topological density wave phases. By varying the spatial range of the nonlocal interaction, we find various chiral density waves with spontaneous timereversal symmetry breaking, whose quasiparticles form threedimensional quantum Hall and Weyl semimetal states. Remarkably, certain density waves even exhibit mixed topologies beyond the existing topological classification. Our results suggest gapless sermonic states with longrange interactions could exhibit far richer topology than previously expected. Reference: Xiaopeng Li, S. Das Sarma, Nat. Comms. 6:7137 (2015) [Preview Abstract] 
Thursday, May 26, 2016 9:00AM  9:12AM 
M9.00006: Analog simulation of Weyl particles with cold atoms Mihail Rabinovic, Daniel Suchet, Thomas Reimann, Norman Kretzschmar, Franz Sievers, Christophe Salomon, Jonathan Lau, Carlos Lobo, Olga Goulko, Frederic Chevy The high degree of control of the properties of ultracold gases offers the possibility to study experimentally unconventional manybody systems. An example is given by massless relativistic Weyl fermions, which are of particular interest in high energy and condensed matter physics, where they emerge in the form of low energy excitations of exotic compounds like TaAs. The particular case of harmonically trapped Weyl particles can be mimicked by a lasercooled cloud of $^6\rm{Li}$ trapped in a magnetic quadrupole potential. The nonseparability of this particular potential enables a quasithermalization of the single particle distribution function even in the absence of interactions. Surprisingly, the dynamics features an effective decoupling between the strong trapping axis and the weak trapping plane. We studied both, numerically and experimentally, the relaxation of the excited cloud towards its equilibrium distribution, mapping this dynamics directly to the case of noninteraction massless particles in a harmonic potential. D.~Suchet, M.~Rabinovic, T.~Reimann, et al.\emph{submitted} (2016). [Preview Abstract] 
Thursday, May 26, 2016 9:12AM  9:24AM 
M9.00007: ABSTRACT WITHDRAWN 
(Author Not Attending)

M9.00008: Chiral magnetism and spin liquid Mott insulators induced by synthetic gauge fields Arun Paramekanti, Ciaran Hickey, Lukasz Cincio, Zlatko Papic, Arun VellatSadashivan, Ramanjit Sohal Recent experiments using Ramanassisted tunneling or latticeshaking have realized synthetic gauge fields and optical lattice bands with nontrivial band topology. Here we examine the effect of particle interactions in such bands, focussing on twocomponent fermions with local Hubbard repulsion. We show that interactions can drive the integer quantum Hall insulator into Mott insulating states which possess noncoplanar chiral magnetic textures and even chiral spin liquids with manybody topological order. We establish our results using a combination of mean field theory, strong coupling expansions, numerical exact diagonalization and DMRG methods. We also discuss possible signatures of such noncoplanar orders in Bragg scattering and noise measurements. [Preview Abstract] 
Thursday, May 26, 2016 9:36AM  9:48AM 
M9.00009: Pairing of Fermions with Unequal Effective Charges in an Artificial Magnetic Field Nur Unal, M. O. Oktel Artificial magnetic fields (AMFs) created for ultracold systems depend sensitively on the internal structure of the atoms. In a mixture, each component couples to the AMF with a different charge. This enables the study of BardeenCooperSchrieffer pairing of fermions with unequal effective charges [1]. We investigate the superconducting (SC) transition of a system formed by such pairs as a function of the field strength. We consider a homogeneous twocomponent Fermi gas of unequal charges but equal densities with attractive interactions. We find that the phase diagram is altered drastically compared to the usual equal charge case. First, for some AMFs there is no SC transition and isolated SC phases are formed, reflecting the discrete Landau level (LL) structure. SC phases become reentrant both in AMF and temperature. For extremely high fields where both components are confined to their lowest LLs, the effect of the charge imbalance is suppressed. Charge asymmetry reduces the critical temperature even in the lowfield semiclassical regime. We discuss a pair breaking mechanism due to the unequal Lorentz forces acting on the components of the Cooper pairs to identify the underlying physics. [1] F. Nur \"{U}nal and M. \"{O}. Oktel, Phys. Rev. Lett. 116, 045305 (2016). [Preview Abstract] 
Thursday, May 26, 2016 9:48AM  10:00AM 
M9.00010: Threecomponent FuldeFerrell superfluids in a twodimensional Fermi gas with spinorbit coupling Fang Qin, Fan Wu, Wei Zhang, Wei Yi, GuangCan Guo We investigate the pairing physics of a threecomponent spinorbit coupled (SOC) Fermi gas in two spatial dimensions. The three atomic hyperfine states of the system are coupled by the recently realized synthetic SOC, which mixes different hyperfine states into helicity branches in a momentumdependent manner. As a consequence, the interplay of SOC and the hyperfinestate dependent interactions leads to the emergence of FuldeFerrell (FF) pairing states with finite centerofmass (COM) momenta even in the absence of the Fermisurface asymmetry that is usually mandatory to stabilize an SOCinduced FF state. We show that, for different combinations of spindependent interactions, the ground state of the system can either be the conventional BCS pairing state with zero COM momentum or be the FF pairing states. Of particular interest here is the existence of a threecomponent FF pairing state in which every two out of the three components form FF pairing. We map out the phase diagram of the system and characterize the properties of the threecomponent FF state, such as the order parameters, the gapless contours and the momentum distributions. Based on these results, we discuss possible experimental detection schemes for the interesting pairing states in the system. [Preview Abstract] 
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