Bulletin of the American Physical Society
APS March Meeting 2018
Volume 63, Number 1
Monday–Friday, March 5–9, 2018; Los Angeles, California
Session K34: Precision Many Body Physics IIFocus

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Sponsoring Units: DCOMP DAMOP DCMP Chair: Yuan Huang, Univ of Mass  Amherst Room: LACC 409A 
Wednesday, March 7, 2018 8:00AM  8:36AM 
K34.00001: Two and threebody contacts in the unitary Bose gas Invited Speaker: Zoran Hadzibabic In manybody systems governed by pairwise contact interactions, a wide range of observables is linked by a single parameter, the twobody contact, which quantifies twoparticle correlations. This profound insight has transformed our understanding of strongly interacting Fermi gases. Using Ramsey interferometry, we studied coherent evolution of the resonantly interacting Bose gas, and we show here that it cannot be explained by only pairwise correlations. Our experiments reveal the crucial role of threebody correlations arising from Efimov physics and provide a direct measurement of the associated threebody contact. 
Wednesday, March 7, 2018 8:36AM  8:48AM 
K34.00002: The nature of pairing correlations in the homogeneous unitary Fermi gas Scott Jensen, Christopher Gilbreth, Yoram Alhassid The spinbalanced unitary Fermi gas is a strongly correlated manybody system that exhibits a high superfluid critical temperature of about 0.15 of the Fermi temperature. A pseudogap phase, which has a gapped singleparticle excitation spectrum without offdiagonal longrange order, was proposed but its existence is still debated. To address this, we have carried out accurate finitetemperature auxiliaryfield quantum Monte Carlo calculations of the homogeneous unitary gas on a lattice in the canonical ensemble of fixed particle number. We present results for the heat capacity, condensate fraction, model independent energystaggering pairing gap, and static spin susceptibility as a function of temperature. We observe no clear signatures of a gapped phase above the superfluid critical temperature. 
Wednesday, March 7, 2018 8:48AM  9:00AM 
K34.00003: Computational Aspects of CanonicalEnsemble AuxiliaryField Monte Carlo for the Unitary Fermi Gas Christopher Gilbreth, Scott Jensen, Yoram Alhassid The unitary Fermi gas, defined as a collection of spin1/2 particles interacting at zero range with infinite scattering length, is of interest to a wide variety of problems in manybody physics. Quantum Monte Carlo (QMC) methods are the only theoretical methods with controllable systematic errors for studying such systems and have been widely applied to predict their properties. Calculations at finite temperature and for fixed particle number are important for studying finitesize systems and for pairing phenomena such as the pseudogap. I will discuss computational aspects of such calculations using auxiliaryfield quantum Monte Carlo (AFMC), including the validity of using a spherical cutoff in the singleparticle momentum, a strategy previously applied to reduce the dimensions of the matrices involved. Without such a cutoff, finitetemperature calculations are considerably more expensive; I will discuss other strategies that can reduce the computational scaling of finitetemperature AFMC calculations. 
Wednesday, March 7, 2018 9:00AM  9:12AM 
K34.00004: BoseEinstein condensation of spinor S=1 bosons Longxiang Liu, Youjin Deng, Anatoly Kuklov The nature of the BEC transition of S=1 spinor bosons is addressed by Monte Carlo Simulations of the field model [1] of threecomponent Bose field characterized by O(6) symmetry, with the ferromagnetic interaction g_{F} breaking the symmetry down to O(3)xU(1) on 3dimensional cubic lattice. This model is relevant to the condensation of ^{87}Rb, ^{39}K and ^{23}Na ultracold atoms. Worm Algorithm [2] is adapted to the system to calculate oneparticle as well as twoparticle correlators, including the interconversion rule when a pair of particles with opposite spins transforms into a pair of atoms with zero spin projection each (and vice versa). At g_{F}=0 the BEC transition is consistent with the O(6) universality class. Using the numerical flowgram method [3], it is shown that at small g_{F} the criticality flows away from the O(6) universality as the system size increases. The universality of the resulting stable fixed point will be discussed. We also find the tricritcal point g_{F}=g_{T} above which the transition becomes discontinuous. 
Wednesday, March 7, 2018 9:12AM  9:24AM 
K34.00005: Confinement transition of the orthogonal semimetal: Emergent QCD_{3} and SO(5) symmetry. Snir Gazit, Chong Wang, Fakher Assaad, Subir Sachdev, Ashvin Vishwanath We discuss a model of Dirac fermions coupled to an Ising gauge theory, for which recent Monte Carlo simulations have observed a direct and continuous transition into a confined, symmetry broken phase. This result was surprising since, without fine tuning of parameters, a first order or split transition is expected, with symmetry breaking preceding confinement. We develop a field theory description of the direct transition involving a nonabelian (SU(2)) gauge group and identify its consequences. In particular, an emergent SO(5) symmetry is predicted at the transition. We verify this prediction in quantum Monte Carlo simulations and contrast our findings with the standard GrossNeveau transition. 
Wednesday, March 7, 2018 9:24AM  9:36AM 
K34.00006: Emergence of Luttinger Liquid Behavior of a Superclimbing Dislocation Max Yarmolinsky, Liu Longxiang, Anatoly Kuklov A generic edge dislocation with superfluid core in solid ^{4}He represents a nonLuttinger liquid according to the elementary scaling dimensional analysis because its compressibility diverges as square of the dislocation length[1]. Monte Carlo simulations [2], however, reveal that such a dislocation develops finite compressibility as temperature is lowered and its size increases. For certain parameters the dislocation can undergo a transition into insulating state regardless of the filling factor. An external macroscopically small bias by chemical potential can restore the nonLuttinger behavior [1]. The analysis [2] has been conducted in a simplified model ignoring longrange forces between quantum jogs. Current simulations including such forces show that the main features observed in [2] do not change qualitatively. Experimental verifications of these features are proposed in connection with the ongoing efforts to understand the superflowthroughsolid as well as the syringe effects in solid ^{4}He. 
Wednesday, March 7, 2018 9:36AM  9:48AM 
K34.00007: 2D topological orders with gapped boundaries  a quantum informational study Bowen Shi, YuanMing Lu Excitations of topological orders could leave footprints on subsystems away from them. We develop a quantum informational tool: information convex (a suitably selected convex set of reduced density matrices on a chosen subsystem) to capture such footprints. To illustrate the usefulness and topological invariant structures of information convex, we study 2D quantum double models, and discuss some rich properties of gapped boundaries in nonAbelian models. Finally, we discuss how the structures of information convex may be observed by ultracold atom experiments. 
Wednesday, March 7, 2018 9:48AM  10:00AM 
K34.00008: Classifying three dimensional symmetry enriched topological phases via topological field theory Shangqiang Ning, ZhengXin Liu, Peng Ye While two dimensional symmetry enriched topological phases(SET) have been intensively studied, many issues of the three dimensional ones are still open. In this talk, we are going to focus on the 3 dimensinoal abelian topological order enriched by abelian symmetries and try to classify those phases via topological field theory. Three dimensional ablian topological orders can be described by topological BF field theory. Different abelian topological orders correspond inequivalent BF field theories. We found that imposing the symmetry in the topological theory, the number of inequivalent theories without breaking symmetry may increase, saying the topological orders are enriched. To classify all these inequivalent 3D SET phases, we gauge the symmetry and study the resulting phases. 
Wednesday, March 7, 2018 10:00AM  10:12AM 
K34.00009: Topological Mott Insulators in Certain Frustrated Lattices Vito Scarola, Mengsu Chen, HoiYin Hui, Sumanta Tewari Topological phases typically encode topology at the level of the single particle band structure. But a remarkable new class of models shows that quantum anomalous Hall effects can be driven exclusively by interactions, while the parent noninteracting band structure is topologically trivial. Unfortunately, these models have so far relied on interactions that do not spatially decay and are therefore unphysical. We study twodimensional models of spinless fermions on frustrated lattices (decorated honeycomb and kagome). Using complementary methods, meanfield theory and exact diagonalization, we find a robust quantum anomalous Hall phase arising from spatially decaying interactions, including a screened Coulomb interaction. Our findings indicate that interactions alone can, in principle, drive topologically trivial singleparticle states into topological phases in certain frustrated lattice models. These models in turn offer a starting point to engineer the quantum anomalous Hall phases in twodimensional ferromagnets. 
Wednesday, March 7, 2018 10:12AM  10:24AM 
K34.00010: Stronglyinteracting rotating bosons via complex stochastic quantization Casey Berger, Joaquin Drut Quantum field theories with a complex action suffer from a sign problem in stochastic nonperturbative treatments, making many systems of great interest  such as polarized or massimbalanced fermions and quantum chromodynamics (QCD) at finite baryon density  extremely challenging to treat numerically. Another such system is that of multiple bosons at finite angular momentum; experimentalists have successfully achieved vortex formation in supercooled bosonic atoms, and have measured quantities of interest such as the moment of inertia. However, the rotation results in a complex action, making the usual numerical treatments of the theory unusable. In this work, we use complex stochastic quantization, a method that has gained much attention in lattice QCD, to circumvent the sign problem and calculate basic properties of rotating bosons with strong interactions. 
Wednesday, March 7, 2018 10:24AM  10:36AM 
K34.00011: Phase Diagram of the 5/2 Fractional Quantum Hall State in Presence of Landau Level Mixing Revisited Kiryl Pakrouski, Michael Peterson, Ariana Valdez, Edward Rezayi We revisit the quantum phase diagram of the 5/2 fractional quantum Hall state in semiconductor quantum wells at finite magnetic field and finite width of the 2D electron gas. The model includes higher 3body pseudopotentials that were shown (PRL 119, 026801 (2017)) to be important for the Pfaffian versus antiPfaffian competition. We identify the ground state throughout the phase diagram by examining the energetic and entanglement properties by means of exact diagonalisation. 
Wednesday, March 7, 2018 10:36AM  10:48AM 
K34.00012: Quantum quench in fermionic systems with extended d+id pairing Ammar Kirmani, Maxim Dzero We consider the problem of nonadiabatic dynamics of 2D fermions with extended d+id pairing following a sudden quantum quench of coupling constant. Our approach is based on Lax vector and integrability of underlying classical model. Depending upon number of complex roots of Lax equation, we identify three regions in our phase diagram defining behavior of extended d+id order paramete △(t) at long times following quantum quench. Region 1 is characterized by vanishing order parameter, in region 2 order parameter asymptotes to a constant and periodically oscillates in region 3 at long times. We also perform numerical integration of extended d+id manybody Green's functions E.O.M. following a quantum quench and found it in exact agreement with the result obtained by Lax root method. Dynamics of order parameter for nonintegrable case i.e. d+id, following quantum quenches, will also be presented and compared against extended d+id results . 
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