Bulletin of the American Physical Society
APS March Meeting 2018
Monday–Friday, March 5–9, 2018; Los Angeles, California
Session L34: Precision Many Body Physics IIIFocus

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Sponsoring Units: DCOMP DAMOP DCMP Chair: Vito Scarola, Virginia Tech Room: LACC 409A 
Wednesday, March 7, 2018 11:15AM  11:51AM 
L34.00001: Siteresolved microscopy of ultracold FermiHubbard systems in new regimes Invited Speaker: Waseem Bakr The ability to probe and manipulate ultracold fermions in optical lattices at the atomic level using quantum gas microscopes has enabled quantitative studies of FermiHubbard models in a temperature regime that is challenging for stateoftheart numerical simulations. Experiments have focused on spinbalanced gases of repulsively interacting atoms with the hope of elucidating phenomena in hightemperature superconductors. In this talk, I will present experiments that explore the Hubbard model in two new regimes: repulsive gases with spinimbalance and attractive spinbalanced gases. In the first regime, we observe canted antiferromagnetism at halffilling, with stronger correlations in the direction orthogonal to the magnetization. Away from halffilling, the polarization of the gas exhibits nonmonotonic behavior with doping, resembling the behavior of the magnetic susceptibility of the cuprates. The attractive Hubbard model studied in the second set of experiments is the simplest theoretical model for studying pairing and superconductivity of fermions in a lattice. Our measurements on the normal state reveal checkerboard chargedensity wave correlations close to halffilling. The chargedensitywave correlations are a sensitive thermometer in the low temperature regime relevant for future studies of inhomogeneous superfluid phases in spinimbalanced attractive gases. 
Wednesday, March 7, 2018 11:51AM  12:03PM 
L34.00002: Towards quantum simulation with circular Rydberg atoms Guillaume Roux , Thanh Long Nguyen , JeanMichel Raimond , Clément Sayrin , Rodrigo Cortiñas , Tigrane CantatMoltrecht , Frédéric Assemat , Igor Dotsenko , Sébastien Gleizes , Serge Haroche , Michel Brune We propose to realize a quantum simulator of spin arrays, based on lasertrapped circular Rydberg atoms. The atoms are protected from spontaneous emission decay, reaching lifetimes in the minute range. A defectfree chain of 40 atoms can be prepared thanks to an innovative technique, that bears resemblance with evaporative cooling, based on van der Waals interaction between the atoms. 
Wednesday, March 7, 2018 12:03PM  12:15PM 
L34.00003: Using SingleParticle Content to Distinguish SingleParticle, Collective and Strongly Correlated AtomicScale Quantum Systems Emily Townsend , Tomas Neuman , Javier Aizpurua , Garnett Bryant Linear atomic chains, such as atom chains on surfaces, linear arrays of dopant atoms in semiconductors, or linear molecules, provide ideal testbeds for studying singleparticle, collective (plasmonic) and strongly correlated excitations in the quantum limit for interacting matter systems. We use exact diagonalization to find the manybody excitations of finite (426) atom chains, described by hopping plus longrange electronelectron repulsion and the corresponding electroncore attraction. A combination of criteria involving the manybody state transition dipole moment, balance, dynamical response, induced transition charge density and singleparticle content can be used to characterize the excitations of atomicscale systems as a function of the electronelectron interaction strength. The singleparticle content clearly displays distinct transitions from a regime for singleparticle excitations to collective then to strongly correlated behavior as the electronelectron interaction increases and shows how this transition takes place. This allows us to define and investigate regimes that support quantum plasmon excitations. The onset of quantum plasmons in small atomicscale systems and the relation to Luttinger liquid theory is discussed. 
Wednesday, March 7, 2018 12:15PM  12:27PM 
L34.00004: Precision auxiliaryfield quantum Monte Carlo computations of Rashba spinorbit coupling in interacting manybody systems Peter Rosenberg , Hao Shi , Shiwei Zhang We describe the treatment of Rashba spinorbit coupling (SOC) in interacting manyfermion systems within the auxiliaryfield quantum Monte Carlo (AFQMC) framework, and present a set of illustrative results. We show that this technique can be applied to a wide range of systems, including the Fermi gas in the continuum and the lattice, with attractive or repulsive interactions. In the unpolarized, attractive case our results provide a numerically exact description of the groundstate of the Fermi gas in the continuum [1], and the lattice [2]. For the repulsive case a constraint is applied and we perform a set of benchmark calculations that achieve similar accuracy to calculations without SOC [3]. These developments enable highprecision AFQMC simulations of many of the novel Hamiltonians currently being engineered in ultracold atoms, and provide a general approach for predictive computations in models and materials to study the interplay of SOC and strong correlation. In addition to establishing a new set of benchmarks, this technique offers quantitative numerical insight to guide the search for topological phases. 
Wednesday, March 7, 2018 12:27PM  12:39PM 
L34.00005: New Probes of the tJ Model in Quantum Gas Microscopes Annabelle Bohrdt , Daniel Greif , Eugene Demler , Michael Knap , Fabian Grusdt In this talk I’m going to present a measurement scheme for the singleparticle spectral function that allows quantum gas microscopes to perform experiments similar to angleresolved photoemission spectroscopy in conventional condensed matter systems. As an example for possible applications, we numerically calculate the spectrum of a single hole excitation in 1D tJ models with isotropic and anisotropic antiferromagnetic couplings. A sharp asymmetry in the distribution of spectral weight appears when a hole is created in an isotropic Heisenberg spin chain. This effect slowly vanishes for anisotropic spin interactions and disappears completely in the case of pure Ising interactions. I will introduce a slavefermion mean field theory, which provides an intuitive physical picture for this behavior. As an outlook, I will discuss possible measurements in two dimensions. 
Wednesday, March 7, 2018 12:39PM  12:51PM 
L34.00006: The Halon: A Quasiparticle Featuring Critical Charge Fractionalization Kun Chen , Yuan Huang , Youjin Deng , Boris Svistunov The halon is a special critical state of an impurity in a quantumcritical environment. The hallmark of the halon physics is that a welldefined integer charge gets fractionalized into two parts: a microscopic core with halfinteger charge and a critically large halo carrying a complementary charge of ±1/2. The halon phenomenon emerges when the impurity–environment interaction is finetuned to the vicinity of a boundary quantum critical point (BQCP), at which the energies of two quasiparticle states with adjacent integer charges approach each other. The universality class of such BQCP is captured by a model of pseudospin1/2 impurity coupled to the quantumcritical environment, in such a way that the rotational symmetry in the pseudospin XYplane is respected, with a small local “magnetic” field along the pseudospin zaxis playing the role of control parameter driving the system away from the BQCP. On the approach to BQCP, the halfinteger projection of the pseudospin on its zaxis gets delocalized into a halo of critically divergent radius, capturing the essence of the phenomenon of charge fractionalization. With largescale Monte Carlo simulations, we confirm the existence of halons—and quantify their universal features—in O(2) and O(3) quantum critical systems. 
Wednesday, March 7, 2018 12:51PM  1:03PM 
L34.00007: Dipolar extended FermiHubbard Model in twodimensions Raimundo Rocha Dos Santos , Tiago MendesSantos , Rubem Mondaini , Thereza Paiva The ability to cool bosonic and fermionic atoms down to ultra cold temperatures in optical lattices has enabled the experimental emulation of model Hamiltonians for strongly correlated systems. Unlike in Condensed Matter systems, one has control over the model parameters such as interaction strength, hopping amplitude, and population imbalance. A recent experimental development in cold gases is the ability to create quantum degenerate bosonic and fermionic gases of magnetic atoms, leading to the study of magnetic dipolar interactions. The extended BoseHubbard model was recently emulated with ^{168}Er atoms in an optical lattice. The study of fermionic systems with anisotropic interactions beyond onsite is clearly in order. Here we use the Lanczos method to explore the ground state phase diagram of the dipolar extended FermiHubbard Model at halffilling and twodimensions. The anisotropic character of the dipoledipole interaction, nearestneighbour as well as nextnearestneighbour interactions are taken into account. We observe quantum phase transitions between Antiferromagnetic and different ChargeDensity Waves phases. 
Wednesday, March 7, 2018 1:03PM  1:15PM 
L34.00008: An Auxiliary Field Quantum Monte Carlo study of the Hubbard Kanamori model Hongxia Hao , Brenda Rubenstein , Hao Shi In the physics of stronglycorrelated manyelectron systems, the Hubbard Kanamori model has been extensively studied as a prototype for transitionmetal oxides. The model is multiorbital in nature and contains Hund’s coupling terms. As a result, it may manifest metalinsulator transitions and hightemperature superconductivity. Due to the sign problem, it is mainly studied through the framework of Dynamical MeanField Theory (DMFT). We study the model using the ground state Auxiliary Field Quantum Monte Carlo (AFQMC) method. The HubbardStratonovich transformation is applied to the Hund’s coupling and pairexchange terms. The Constrained Path Approximation is used to control the sign problem. A systematic test is carried out on the accuracy of the approach. The ground state properties of the model will be discussed. 
Wednesday, March 7, 2018 1:15PM  1:27PM 
L34.00009: Dynamical MeanField Theory of Superconductivity in the HubbardHolstein Model TaeHo Park , HanYong Choi We present a study of the halffilled HubbardHolstein model with superconducting order parameter employing the dynamical meanfield theory in combination with the numerical renormalization group. The HubbardHolstein model is a prototype model for understanding the interplay between the local Coulomb repulsion U and the electronphonon coupling g. The ground state is metallic when both U and g are small, but is a MottHubbard insulator (MHI) when U is larger than the critical value of the Coulomb repulsion U_{c} and a bipolaron insulator (BPI) when g is larger than the critical value of the electronphonon coupling g_{c}. Here, we investigate the interplay between the electronelectron and electronphonon interactions in superconducting state emerging around the phase boundary between metallic and insulating states. In particular, the effect of phonon softening on supercondcutivity is investigated in the strong correlation regime. The variation of the superconductivity is also probed by changing the phonon frequency from adiabatic to nonadiabatic regimes. 
Wednesday, March 7, 2018 1:27PM  1:39PM 
L34.00010: The Integrability and Thermodynamics of a TwoImpurity Anderson Model Caitlin Carpenter , Natan Andrei The integrability of certain quantum impurity models has allowed for examination of nonequilibrium transport properties such as the IV curves of systems of quantum dots connected to Fermi sealike leads. Experimental realizations of these systems with coldatom gases and artificial atoms have shown that understanding the nonperturbative effects of the strong correlations in these models is essential to properly capturing the details of the systems' response to bias voltages or other driving. 
Wednesday, March 7, 2018 1:39PM  1:51PM 
L34.00011: An exactly solvable BCSHubbard Model in arbitrary dimensions Zewei Chen , Xiaohui Li , Tai Kai Ng In this talk, we present an exact solvable BCSHubbard model in arbitrary dimensions. The model describes a pwave BCS superconductor with equal spin pairing moving on a bipartite (cubic, square etc.) lattice with onsite Hubbard interaction U. We show that the model becomes exactly solvable for arbitrary U when the BCS pairing amplitude Delta equals the hopping amplitude t. In this limit, the model is nonmagnetized without interaction while it becomes an antiferromagnet for arbitrary small interaction. The solitonic excitation of this model shows a transition from spin 1/2 fermionic excitation to spin 1 bosonic excitation. The construction of the exact solution is parallel to the exactly solvable Kitaev honeycomb model for S=1/2 quantum spins and can be viewed as a generalization of Kitaev's construction to S=1/2 interacting lattice fermions [12]. The BCSHubbard model discussed is just an example of a large class of exactly solvable lattice fermion models that can be constructed similarly. Our arxiv preprint is available at Ref.[3]. 
Wednesday, March 7, 2018 1:51PM  2:03PM 
L34.00012: Random Matrix Theory for NonHermitian Hamiltonians S. Vijay , Liang Fu We study the random matrix theory for nonHermitian Hamiltonians for dissipative systems. We derive the universal behavior of the level repulsion of the complex eigenvalues of such a nonHermitian Hamiltonian  which deviates significantly from the level statistics of a random, Hermitian Hamiltonian  in the absence of symmetries, or in the presence of timereversal symmetry with T^{ 2} = ±1. We compute the density of states, which develops tails ρ(ε) ~ 1/ε^{2} and a loss of spectral weight at low energies, proportional to the strength of nonHermiticity. We conclude by discussing scattering experiments in which these effects can be measured. 
Wednesday, March 7, 2018 2:03PM  2:15PM 
L34.00013: Quantum Phase Diagram of the Hamiltonian Mean Field Model Ryan Plestid , James Lambert , Duncan O'Dell , Erik Sorensen Quantum many body systems with long range interactions (LRIs) are increasingly both being realized in laboratory experiments, and recieving theoretical interest. The Hamiltonian Mean Field model (HMFm) is a 1D model that has been extremely successful at helping to shed light on classical features of LRI systems such as selfgravitating fluids, and neutral plasmas. In this talk we investigate the bosonic HMFm's quantum phase diagram. Ignoring density and phase fluctuations, Chavanis (EPJ 2011) argued that a quantum phase transition, driven by a competition between LRIs and quantum pressure, is present. The ordered phase breaks translational symmetry, and is naively forbidden by the MerminWagner theorem, however this allowed for LRI systems (e.g. Maghrebi PRL 119). In this talk we will discuss how to go beyond the meanfield approximation used by Chavanis, both numerically and analytically, and investigate the role of fluctuations in modifying the model's phase diagram, and the ultimate fate of the ordered phase. 
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