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 three-body contacts in the unitary Bose gas Invited Speaker: Zoran Hadzibabic In many-body systems governed by pairwise contact interactions, a wide range of observables is linked by a single parameter, the two-body contact, which quantifies two-particle 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 three-body correlations arising from Efimov physics and provide a direct measurement of the associated three-body 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 spin-balanced unitary Fermi gas is a strongly correlated many-body system that exhibits a high superfluid critical temperature of about 0.15 of the Fermi temperature. A pseudogap phase, which has a gapped single-particle excitation spectrum without off-diagonal long-range order, was proposed but its existence is still debated. To address this, we have carried out accurate finite-temperature auxiliary-field 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 energy-staggering 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 Canonical-Ensemble Auxiliary-Field Monte Carlo for the Unitary Fermi Gas Christopher Gilbreth, Scott Jensen, Yoram Alhassid The unitary Fermi gas, defined as a collection of spin-1/2 particles interacting at zero range with infinite scattering length, is of interest to a wide variety of problems in many-body 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 finite-size systems and for pairing phenomena such as the pseudogap. I will discuss computational aspects of such calculations using auxiliary-field quantum Monte Carlo (AFMC), including the validity of using a spherical cutoff in the single-particle momentum, a strategy previously applied to reduce the dimensions of the matrices involved. Without such a cutoff, finite-temperature calculations are considerably more expensive; I will discuss other strategies that can reduce the computational scaling of finite-temperature AFMC calculations. |
Wednesday, March 7, 2018 9:00AM - 9:12AM |
K34.00004: Bose-Einstein 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 three-component Bose field characterized by O(6) symmetry, with the ferromagnetic interaction gF breaking the symmetry down to O(3)xU(1) on 3-dimensional cubic lattice. This model is relevant to the condensation of 87Rb, 39K and 23Na ultracold atoms. Worm Algorithm [2] is adapted to the system to calculate one-particle as well as two-particle 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 gF=0 the BEC transition is consistent with the O(6) universality class. Using the numerical flowgram method [3], it is shown that at small gF 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 gF=gT above which the transition becomes discontinuous. |
Wednesday, March 7, 2018 9:12AM - 9:24AM |
K34.00005: Confinement transition of the orthogonal semimetal: Emergent QCD3 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 Gross-Neveau 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 4He represents a non-Luttinger 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 non-Luttinger behavior [1]. The analysis [2] has been conducted in a simplified model ignoring long-range 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 superflow-through-solid as well as the syringe effects in solid 4He. |
Wednesday, March 7, 2018 9:36AM - 9:48AM |
K34.00007: 2D topological orders with gapped boundaries - a quantum informational study Bowen Shi, Yuan-Ming 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 non-Abelian 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, Zheng-Xin 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, Hoi-Yin 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 non-interacting 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 two-dimensional models of spinless fermions on frustrated lattices (decorated honeycomb and kagome). Using complementary methods, mean-field 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 single-particle 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 two-dimensional ferromagnets. |
Wednesday, March 7, 2018 10:12AM - 10:24AM |
K34.00010: Strongly-interacting 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 mass-imbalanced 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 3-body pseudopotentials that were shown (PRL 119, 026801 (2017)) to be important for the Pfaffian versus anti-Pfaffian 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 non-adiabatic dynamics of 2-D 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 many-body 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 non-integrable case i.e. d+id, following quantum quenches, will also be presented and compared against extended d+id results . |
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