Arxiv Selection Oct 2018
Oct 1- Oct 7 Xuguang Yue, Oct 8- Oct 16 Haiyuan Zou, Oct 17- Oct 23 Zehan Li, Oct 24-Oct 30 Jiansong Pan
Contents
Oct. 30
arXiv:1810.12229 [pdf, other]
Supersolid behaviour of a dipolar Bose-Einstein condensate confined in a tube
Santo Maria Roccuzzo, Francesco Ancilotto
Comments: 5 pages, 4 figures
Subjects: Quantum Gases (cond-mat.quant-gas)
Motivated by a recent experiment [L.Chomaz et al., Nature Physics 14, 442 (2018)], we perform numerical simulations of a dipolar Bose-Einstein Condensate (BEC) in a tubular confinement at T=0 within Density Functional Theory, where the beyond-mean-field correction to the ground state energy is included in the Local Density Approximation. We study the excitation spectrum of the system by solving the corresponding Bogoliubov-de Gennes equations. The calculated spectrum shows a roton minimum, and the roton gap decreases by reducing the effective scattering length. As the roton gap disappears, the system spontaneously develops in its ground-state a periodic, linear structure formed by denser clusters of atomic dipoles immersed in a dilute superfluid background. This structure shows the hallmarks of a supersolid system, i.e. (i) a finite non-classical translational inertia along the tube axis and (ii) the appearance, besides the phonon mode, of the Nambu-Goldstone gapless mode corresponding to phase fluctuations, and related to the spontaneous breaking of the gauge symmetry. A further decrease in the scattering length eventually leads to the formation of a periodic linear array of self-bound droplets.
arXiv:1810.11958 (cross-list from hep-th) [pdf, other]
Quantum Epidemiology: Operator Growth, Thermal Effects, and SYK
Xiao-Liang Qi, Alexandre Streicher
Comments: 31 pages, 10 figures
Subjects: High Energy Physics - Theory (hep-th); Statistical Mechanics (cond-mat.stat-mech); Strongly Correlated Electrons (cond-mat.str-el); Quantum Physics (quant-ph)
In many-body chaotic systems, the size of an operator generically grows in Heisenberg evolution, which can be measured by certain out-of-time-ordered four-point functions. However, these only provide a coarse probe of the full underlying operator growth structure. In this article we develop a methodology to derive the full growth structure of fermionic systems, that also naturally introduces the effect of finite temperature. We then apply our methodology to the SYK model, which features all-to-all q-body interactions. We derive the full operator growth structure in the large q limit at all temperatures. We see that its temperature dependence has a remarkably simple form consistent with the slowing down of scrambling as temperature is decreased. Furthermore, our finite-temperature scrambling results can be modeled by a modified epidemic model, where the thermal state serves as a vaccinated population, thereby slowing the overall rate of infection.
arXiv:1810.12050 (cross-list from cond-mat.quant-gas) [pdf, other]
Dissipation-induced topological insulators: A no-go theorem and a recipe
Moshe Goldstein
Comments: 12 pages, 7 figures
Subjects: Quantum Gases (cond-mat.quant-gas); Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Strongly Correlated Electrons (cond-mat.str-el)
Nonequilibrium conditions are traditionally seen as detrimental to the appearance of quantum-coherent many-body phenomena, and much effort is often devoted to their elimination. Recently this approach has changed: It has been realized that driven-dissipative could be used as a resource. By proper engineering of the reservoirs and their couplings to a system, one may drive the system towards desired quantum-correlated steady states, even in the absence of internal Hamiltonian dynamics. An intriguing category of equilibrium many-particle phases are those which are distinguished by topology rather than by symmetry. A natural question thus arises: which of these topological states can be achieved as the result of purely dissipative Lindblad-type (Markovian) evolution? Beside its fundamental importance, it may offer novel routes to the realization of topologically-nontrivial states in quantum simulators, especially ultracold atomic gases. In this work I go beyond previous studies in giving a general answer to this question in the context of Gaussian ("integer") topological states, concentrating on 2D Chern insulators as the main example. On the one hand I prove a no-go theorem which shows that such dynamics cannot lead to a topological robust (gapped Liouvillian) unique pure steady state as the result of finite-range Liouvillian. On the other hand, I construct a recipe showing that, under the above conditions, a pure topological steady state may result if exponetially-local Liouvillian is allowed. If strictly local evolution is insisted upon, a mixed steady state arbitrarily close to the desired pure state may be obtained. I will also show how such dynamics could be realized with ultracold atoms and similar systems, and how the resulting states may be detected and topologically-classified. Extension to other types of topological insulators and superconductors is also discussed.
Oct. 29
arXiv:1810.11086 [pdf, other]
Sign-changing photon-mediated atom interactions in multimode cavity QED
Yudan Guo, Ronen M. Kroeze, Varun V. Vaidya, Jonathan Keeling, Benjamin L. Lev
Comments: 6 pages, 4 figures, supplemental materials 2 pages
Subjects: Quantum Gases (cond-mat.quant-gas); Quantum Physics (quant-ph)
Sign-changing interactions constitute a crucial ingredient in the creation of frustrated many-body systems such as spin glasses. We present here the demonstration of a photon-mediated sign-changing interaction between Bose-Einstein condensed (BEC) atoms in a confocal cavity. The interaction between two atoms is of an unusual, nonlocal form proportional to the cosine of the inner product of the atoms' position vectors. This interaction arises from the differing Gouy phase shifts of the cavity's degenerate modes. Moreover, these Gouy phase anomalies induce an extra pattern of Z_2-symmetry-breaking in the atomic density-wave self-ordering that arises from a nonequilibrium Dicke-type phase transition in the system. This state is detected via the holographic imaging of the cavity's superradiant emission. Together with Ref. [1], we explore this interaction's influence on superradiant phase transitions in multimode cavities. Employing this interaction in cavity QED spin systems may enable the creation of artificial spin glasses and quantum neural networks.
arXiv:1810.11266 [pdf, ps, other]
Fermi surface instabilities of symmetry-breaking and topological types on the surface of a three-dimensional topological insulator
Subhajit Sarkar
Comments: 16 pages, 5 Figures, Submitted for publication. Comments and criticism are welcome
Subjects: Strongly Correlated Electrons (cond-mat.str-el); Other Condensed Matter (cond-mat.other)
The emergence of the Pomeranchuk instability (PI) in a Helical Fermi liquid (HFL) residing on the surface of a three-dimensional topological insulator (3D TI) is addressed at the mean-field level. An expression for the PI condition is derived in terms of a few microscopic parameters in each angular momentum channel corresponding to a central interaction between the Fermions. It is found that because of the presence of strong spin-orbit coupling the Landau parameter, F¯l corresponding to a particular angular momentum channel l depends not only on the interaction in the same channel but also interactions in (l+1) and (l−1) channels. The analysis presented here automatically excludes the l=1 PI in a non-Galilean invariant Fermi liquid. It is also found that the competing PIs can only be avoided till the appearance of l=2 PI. In this case, the corresponding nematic instability can even be achieved in the l=1 angular momentum channel. The range of interaction between the electrons plays a pivotal role in bringing out the PIs. This is established by analysing a few realistic profiles of the interaction. Another class of instability, involving a change in the topology of the Fermi surface without breaking the rotational symmetry, is found which competes with the PIs. Quantum phase transition originating from this instability is quite similar to the Lifshitz transition but is driven by electron-electron interaction. Possible connections of this instability with experiments are also described briefly.
Oct. 26
arXiv:1810.10545 (cross-list from cond-mat.stat-mech) [pdf, other]
Wigner Function and Entanglement Entropy for Bosons from Non-Equilibrium Field Theory
Ahana Chakraborty, Rajdeep Sensarma
Comments: 5+7 Pages, 2+2 Figures
Subjects: Statistical Mechanics (cond-mat.stat-mech); Quantum Gases (cond-mat.quant-gas); Quantum Physics (quant-ph)
We propose a new method of calculating entanglement entropy of a many-body interacting Bosonic system (open or closed) in a field theoretic approach without replica methods. The Wigner function and Renyi entropy of a Bosonic system undergoing arbitrary non-equilibrium dynamics can be obtained from its Wigner characteristic function, which we identify with the Schwinger Keldysh partition function in presence of quantum sources turned on at the time of measurement. For non-interacting many body systems, starting from arbitrary density matrices, we provide exact analytic formulae for Wigner function and entanglement entropy in terms of the single particle Green's functions. For interacting systems, we relate the Wigner characteristic to the connected multi-particle correlators of the system. We use this formalism to study the evolution of an open quantum system from a Fock state with negative Wigner function and zero entropy, to a thermal state with positive Wigner function and finite entropy. The evolution of the Renyi entropy is non-monotonic in time for both Markovian and non-Markovian dynamics. The entropy is also found to be anti-correlated with negativity of the Wigner function of a 2 -mode open quantum system.
Oct. 25
arXiv:1810.10202 (cross-list from quant-ph) [pdf, ps, other]
Searching for Signatures of Quantum Gravity in Quantum Gasses
Simon A. Haine
We propose a scheme for testing the quantum nature of the gravitational field with an ensemble of ultra-cold atoms. The use of many microscopic particles may circumvent some of the experimental obstacles encountered in recent proposals involving a pairs of particles with mesoscopic mass. We employ multi-parameter estimation techniques, including the quantum and classical Fisher information to provide a criteria for the observability of the quantum effects, and compare to other recently proposed schemes. Crucially, we find that by preparing the appropriate initial state, interactions mediated via a quantum-valued gravitational field provide a signature that is distinct from classical gravitational interactions. We find that a test with ultra-cold atoms would be challenging, but not implausible with moderate improvements of current experimental techniques.
Subjects: Quantum Physics (quant-ph); Quantum Gases (cond-mat.quant-gas); General Relativity and Quantum Cosmology (gr-qc)
Oct. 24
arXiv:1810.09480 [pdf, other]
Many-body exceptional points in colliding condensates
Mati Aharonyan, Emanuele G. Dalla Torre
Comments: 9 pages, submitted to the special issue on "Quantum Dynamics and Resonances in Chemistry and Physics" in Molecular Physics
Subjects: Quantum Gases (cond-mat.quant-gas); Quantum Physics (quant-ph)
Exceptional points describe the coalescence of the eigenmodes of a non-Hermitian matrix. When an exceptional point occurs in the spectrum of a many-body system, it generically leads to a dynamical instability with a finite wavevector [N. Bernier et al. , Phys. Rev. Lett. 113, 065303 (2014)]. Here, we study exceptional points in the context of the counterflow instability of colliding Bose-Einstein condensates. We show that the instability of this system is due to an exceptional point in the Bogoliubov spectrum. We further clarify the connection of this effect to the Landau criterion of superfluidity and to the scattering of classical particles. We propose an experimental setup to directly probe this exceptional point, and demonstrate its feasibility with the aid of numerical calculations. Our work fosters the observation of exceptional points in nonequilibrium many-body quantum systems.
Oct. 23
arXiv:1810.09110 [pdf, ps, other]
Excitation of the Higgs Mode in a Superfluid Fermi Gas in the BCS-BEC Crossover
Jun Tokimoto, Shunji Tsuchiya, Tetsuro Nikuni
Subjects: Quantum Gases (cond-mat.quant-gas)
In quantum many-body systems with spontaneous breaking of continuous symmetries, Higgs modes emerge as collective amplitude oscillations of order parameters. Recently, Higgs mode has been observed in the ultracold Fermi gas. In the present paper, we use the time-dependent Bogoliubov-de Gennes equations to investigate Higgs amplitude oscillations of the superfluid order parameter in a Fermi gas induced by a rapid change of the swave scattering length. In particular, we investigate the Higgs mode with different values of the initial scattering length. We find that the energy of the Higgs mode coincides with the threshold energy of the pair-breaking excitation, and exponent of the power-low decay of the Higgs mode γ continuously changes between γ = −1/2 and γ = −3/2 through the Bardeen-Cooper-Schrieffer-Bose-Einstein condensation (BCS-BEC) crossover. Moreover, we propose the optimal ramp speed of the scattering length for observing the clearest Higgs oscillations
Oct. 22
arXiv:1810.08347 [pdf, other]
Excitations of a vortex line in an elongated dipolar condensate
Au-Chen Lee, D. Baillie, R. N. Bisset, P. B. Blakie
Comments: 8 pages, 4 figures
Subjects: Quantum Gases (cond-mat.quant-gas)
We characterise the properties of a vortex line in an elongated dipolar Bose-Einstein condensate. Increasing the strength of the dipole-dipole interactions (DDIs) relative to the short ranged contact interactions we find that the system crosses over to a self-bound vortex droplet stabilized from collapse by quantum fluctuations. We calculate the quasiparticle excitation spectrum of the vortex state, which is important in characterizing the vortex response, and assessing its stability. When the DDIs are sufficiently strong we find that the vortex is dynamically unstable to quadrupolar modes.
Oct. 19
arXiv:1810.07950 [pdf, other]
The liquid state of one-dimensional Bose mixtures: a quantum Monte-Carlo study
L. Parisi, G. E. Astrakharchik, S. Giorgini
Subjects: Quantum Gases (cond-mat.quant-gas)
By using exact quantum Monte-Carlo methods we calculate the ground-state properties of the liquid phase in one-dimensional Bose mixtures with contact interactions. We find that the liquid state can be formed if the ratio of coupling strengths between inter-species attractive and intraspecies repulsive interactions exceeds a critical value. As a function of this ratio we determine the density where the energy per particle has a minimum and the one where the compressibility diverges, thereby identifying the equilibrium density and the spinodal point in the phase diagram of the homogeneous liquid. Furthermore, in the stable liquid state, we calculate the chemical potential, the speed of sound, as well as structural and coherence properties such as the pair correlation function, the static structure factor and the one-body density matrix, thus providing a detailed description of the bulk region in self-bound droplets
Oct. 18
arXiv:1810.05928 (cross-list from math.AP) [pdf, other]
On a dissipative Gross-Pitaevskii-type model for exciton-polariton condensates
Paolo Antonelli, Peter Markowich, Ryan Obermeyer, Jesus Sierra, Christof Sparber
Comments: 26 pages, 11 figures
Subjects: Analysis of PDEs (math.AP); Quantum Gases (cond-mat.quant-gas); Mathematical Physics (math-ph); Pattern Formation and Solitons (nlin.PS)
Abstract. We study a generalized dissipative Gross-Pitaevskii-type model arising in the description of exciton-polariton condensates. We derive rigorous existence and uniqueness results for this model posed on the one dimensional torus and derive various a-priori bounds on its solution. Then, we analyze in detail the long time behavior of spatially homogenous solutions and their respective steady states. In addition, we will present numerical simulations in the case of more general initial data. We also study the corresponding adiabatic regime which results in a single damped-driven Gross-Pitaveskii equation and compare its dynamics to the one of the full coupled system.
Oct. 17
arXiv:1810.07043 [pdf, other]
Topological charge pumping in the interacting bosonic Rice-Mele model
A.L.C. Hayward, C. Schweizer, M. Lohse, M. Aidelsburger, F. Heidrich-Meisner
Subjects: Quantum Gases (cond-mat.quant-gas)
We investigate topological charge pumping in a system of interacting bosons in the tight-binding limit, described by the Rice-Mele model. An appropriate topological invariant for the many-body case is the change of polarization per pump cycle, which we compute for various interaction strengths from infinite-size matrix-product-state simulations. We verify that the charge pumping remains quantized as long as the pump cycle avoids the superfluid phase. In the limit of hardcore bosons, the quantized pumped charge can be understood from single-particle properties such as the integrated Berry curvature constructed from Bloch states, while this picture breaks down at finite interaction strengths. These two properties – robust quantized charge transport in an interacting system of bosons and the breakdown of a single-particle invariant – could both be measured with ultracold quantum gases extending a previous experiment [Lohse et al., Nature Phys. 12, 350 (2016)]. Furthermore, we investigate the entanglement spectrum of the Rice-Mele model and argue that the quantized charge pumping is encoded in a winding of the spectral flow in the entanglement spectrum over a pump cycle.
Oct. 15
1. arXiv:1810.05538 [pdf, other]
Learning multiple order parameters with interpretable machines
Ke Liu, Jonas Greitemann, Lode Pollet
Comments: 16 pages, 10 figures, 4 tables
Subjects: Statistical Mechanics (cond-mat.stat-mech); Computational Physics (physics.comp-ph)
Machine learning techniques are evolving into an subsidiary tool for studying phase transitions in many-body systems. However, most studies are tied to situations involving only one phase transition and one order parameter. Systems that accommodate multiple phases of coexisting and competing orders, which are common in condensed matter physics, remain largely unexplored from a machine learning perspective. In this paper, we investigate multiclassification of phases using Support Vector Machines (SVMs) and apply a recently introduced kernel method for detecting hidden spin and orbital orders to learn multiple phases and their analytical order parameters. Our focus is on multipolar orders and their tensorial order parameters whose identification is difficult with traditional methods. The importance of interpretability is emphasized for physical applications of multiclassification. Furthermore, we discuss an intrinsic parameter of SVM, the bias, which allows for a special interpretation in the classification of phases, and its utility in diagnosing the existence of phase transitions. We show that it can be exploited as an efficient way to explore the topology of unknown phase diagrams where the supervision is entirely delegated to the machine.
2.arXiv:1810.05332 [pdf, other]
Parallel multicomponent interferometry with a spinor Bose-Einstein Condensate
Pengju Tang, Peng Peng, Zhihan Li, Xuzong Chen, Xiaopeng Li, Xiaoji Zhou
Subjects: Quantum Gases (cond-mat.quant-gas)
Atomic interferometry with high-visibility is of high demand for precision measurements. Here, a parallel multi-component interferometer is achieved by preparing a spin-2 Bose-Einstein condensate of 87Rb atoms confined in a hybrid magneto-optical trap. After the preparation of a spinor Bose- Einstein condensate with spin degrees of freedom entangled, we observe four spatial interference patterns in each run of measurements corresponding to four hyperfine states we mainly populate in the experiment. The atomic populations in different Zeeman sublevels are made controllable using a magnetic-field-pulse induced Majorana transitions. The spatial separation of atoms in different hyperfine states is reached by Stern-Gerlach momentum splitting. The high-visibility of the interference fringes is reached by designing a proper overlap of the wave-packets. Due to uncontrollable phase accumulation in Majorana transitions, the phase of each individual spin is found to be subjected to unreproducible shift in multiple experimental runs. However, the relative phase across different spins is stable, paving a way towards noise-resilient multi-component parallel interferometers.
Oct. 12
1. arXiv:1810.05092 [pdf, other]
Classification of phases for mixed states via fast dissipative evolution
Andrea Coser, David Perez-Garcia
Comments: 45 pages
Subjects: Quantum Physics (quant-ph); Statistical Mechanics (cond-mat.stat-mech); Mathematical Physics (math-ph)
We propose the following definition of topological quantum phases valid for mixed states: two states are in the same phase if there exists a time independent, fast and local Lindbladian evolution driving one state into the other. The underlying idea, motivated by Koenig and Pastawski in 2013, is that it takes time to create new topological correlations, even with the use of dissipation. We show that it is a good definition in the following sense: (1) It divides the set of states into equivalent classes and it establishes a partial order between those according to their level of "topological complexity". (2) It provides a path between any two states belonging to the same phase where observables behave smoothly. We then focus on pure states to relate the new definition in this particular case with the usual definition for quantum phases of closed systems in terms of the existence of a gapped path of Hamiltonians connecting both states in the corresponding ground state path. We show first that if two pure states are in the same phase in the Hamiltonian sense, they are also in the same phase in the Lindbladian sense considered here. We then turn to analyse the reverse implication, where we point out a very different behaviour in the case of symmetry protected topological (SPT) phases in 1D. Whereas at the Hamiltonian level, phases are known to be classified with the second cohomology group of the symmetry group, we show that symmetry cannot give any protection in 1D in the Lindbladian sense: there is only one SPT phase in 1D independently of the symmetry group. We finish analysing the case of 2D topological quantum systems. There we expect that different topological phases in the Hamiltonian sense remain different in the Lindbladian sense. We show this formally only for the ℤn quantum double models.
2. arXiv:1810.05076 [pdf, other]
Dissipative many-body physics of cold Rydberg atoms
O. Morsch, I. Lesanovsky
Comments: 31 pages, 9 figures
Journal-ref: Rivista del Nuovo Cimento 41(7), pp. 383-414 (2018)
Subjects: Quantum Physics (quant-ph); Statistical Mechanics (cond-mat.stat-mech); Atomic Physics (physics.atom-ph)
In the last twenty years, Rydberg atoms have become a versatile and much studied system for implementing quantum many-body systems in the framework of quantum computation and quantum simulation. However, even in the absence of coherent evolution Rydberg systems exhibit interesting and non-trivial many-body phenomena such as kinetic constraints and non-equilibrium phase transitions that are relevant in a number of research fields. Here we review our recent work on such systems, where dissipation leads to incoherent dynamics and also to population decay. We show that those two effects, together with the strong interactions between Rydberg atoms, give rise to a number of intriguing phenomena that make cold Rydberg atoms an attractive test-bed for classical many-body processes and quantum generalizations thereof.
Oct. 11
1. arXiv:1810.04347 [pdf, other]
Semiclassical quench dynamics of Bose gases in optical lattices
Kazuma Nagao, Masaya Kunimi, Yosuke Takasu, Yoshiro Takahashi, Ippei Danshita
Subjects: Quantum Gases (cond-mat.quant-gas); Statistical Mechanics (cond-mat.stat-mech)
We analyze the time evolution of the Bose-Hubbard model after a sudden quantum quench to a weakly interacting regime. Specifically, motivated by a recent experiment at Kyoto University, we numerically simulate redistribution of the kinetic and onsite-interaction energies at an early time, which was observed in non-equilibrium dynamics of ultracold Bose gases in a cubic optical lattice starting with a singly-occupied Mott-insulator state. In order to compute the short-time dynamics corresponding to the experimental situation, we apply the truncated-Wigner approximation (TWA) to the Bose-Hubbard model on a cubic lattice. We show that our semiclassical approach quantitatively reproduces the fast redistribution dynamics. We further analyze spatial spreading of density-density correlations at equal time in the Bose-Hubbard model on a square lattice with a large filling factor. When the system is initially prepared in a coherent state, we find that a propagation velocity of the correlation wave packet in the correlation function strongly depends on the final interaction strength, and it is bounded by twice the maximum group velocity of the elementary excitations. In contrast, when the system is initially in a Mott-insulator state, the propagation velocity of the wave packet is approximately independent of the final interaction strength.
Oct. 10
1. arXiv:1810.03933 [pdf, other]
Ground state properties of interacting Bose polarons
Senne Van Loon, Wim Casteels, Jacques Tempere
Comments: 15 pages, 6 figures
Subjects: Quantum Gases (cond-mat.quant-gas)
We theoretically investigate the role of multiple impurity atoms on the ground state properties of Bose polarons. The Bogoliubov approximation is applied for the description of the condensate resulting in a Hamiltonian containing terms beyond the Fr\"ohlich approximation. The many-body nature of the impurity atoms is taken into account by extending the many-body description for multiple Fr\"ohlich polarons, revealing the static structure factor of the impurities as the key quantity. Within this formalism various experimentally accessible polaronic properties are calculated such as the energy and the effective mass. These results are examined for system parameters corresponding to two recent experimental realizations of the Bose polaron, one with fermionic impurities and one with bosonic impurities.
Oct. 9
1. arXiv:1810.03584 [pdf, other]
String patterns in the doped Hubbard model
Christie S. Chiu, Geoffrey Ji, Annabelle Bohrdt, Muqing Xu, Michael Knap, Eugene Demler, Fabian Grusdt, Markus Greiner, Daniel Greif
Comments: 9+21 pages, 5+10 figures
Subjects: Quantum Gases (cond-mat.quant-gas)
Understanding strongly correlated quantum many-body states is one of the most thought-provoking challenges in modern research. For example, the Hubbard model, describing strongly correlated electrons in solids, still contains fundamental open questions on its phase diagram. In this work we realize the Hubbard Hamiltonian and search for specific patterns within many individual images of realizations of strongly correlated ultracold fermions in an optical lattice. Upon doping a cold-atom antiferromagnet we find signatures of geometric strings, entities suggested to explain the relationship between hole motion and spin order, in both pattern-based and conventional observables. Our results demonstrate the potential for pattern recognition and more advanced computational algorithms including machine learning to provide key insights into cold-atom quantum many-body systems.
Oct. 5
1. arXiv:1810.02337 [pdf, other]
Topological Devil's staircase in atomic two-leg ladders
S. Barbarino, D. Rossini, M. Rizzi, R. Fazio, G. E. Santoro, M. Dalmonte
Subjects: Quantum Gases (cond-mat.quant-gas)
We show that a hierarchy of topological phases in one dimension - a topological Devil's staircase - can emerge at fractional filling fractions in interacting systems, whose single-particle band structure describes a topological or a crystalline topological insulator. Focusing on a specific example in the BDI class, we present a field-theoretical argument based on bosonization that indicates how the system phase diagram, as a function of the filling fraction, hosts a series of density waves. Subsequently, based on a numerical investigation of spectral properties, Wilczek-Zee phases, and entanglement spectra, we show that these phases can support symmetry-protected topological order. In sharp contrast to the non-interacting limit, these topological density waves do not follow the boundary-edge correspondence, as their edge modes are gapped. We then discuss how these results are immediately applicable to models in the AIII class, and to crystalline topological insulators protected by inversion symmetry. Our findings are immediately relevant to cold atom experiments with alkaline-earth atoms in optical lattices, where the band structure properties we exploit have been recently realized.
2. arXiv:1810.02287 (cross-list from cond-mat.stat-mech) [pdf, other]
Entanglement and relative entropies for low-lying excited states in inhomogeneous one-dimensional quantum systems
Sara Murciano, Paola Ruggiero, Pasquale Calabrese
Comments: 27 pages, 7 figures
Subjects: Statistical Mechanics (cond-mat.stat-mech); Quantum Gases (cond-mat.quant-gas); High Energy Physics - Theory (hep-th)
Conformal field theories in curved backgrounds have been used to describe inhomogeneous one-dimensional systems, such as quantum gases in trapping potentials and non-equilibrium spin chains. This approach provided, in a elegant and simple fashion, non-trivial analytic predictions for quantities, such as the entanglement entropy, that are not accessible through other methods. Here, we generalise this approach to low-lying excited states, focusing on the entanglement and relative entropies in an inhomogeneous free-fermionic system. Our most important finding is that the universal scaling function characterising these entanglement measurements is the same as the one for homogeneous systems, but expressed in terms of a different variable. This new scaling variable is a non-trivial function of the subsystem length and system's inhomogeneity that is easily written in terms of the curved metric. We test our predictions against exact numerical calculations in the free Fermi gas trapped by a harmonic potential, finding perfect agreement.
Oct. 4
1. arXiv:1810.01852 (cross-list from quant-ph) [pdf, ps, other]
Detecting the entanglement of vortices in ultracold bosons with artificial gauge fields
Li Dai, Lin Xia, Lin Zhuang, Wu-Ming Liu
Comments: 10 pages, 5 figures
Subjects: Quantum Physics (quant-ph); Quantum Gases (cond-mat.quant-gas); Strongly Correlated Electrons (cond-mat.str-el); Superconductivity (cond-mat.supr-con)
The entanglement of vortices in a two-dimensional Bose-Hubbard model with artificial gauge fields is investigated using the exact diagonalization techniques. We propose an effective Hamiltonian for the spin-spin interactions between vortices responsible for this entanglement, and show that the entanglement can be detected through the quantum interference of the bosons in the vortex centers achieved using the Raman coupling and the quantum gas microscope. The strong bosonic coherence between the vortex centers originates from the charge-density wave order in the vortex core. It is robust against the varying of the pinning strength for the vortices to a wide range, and the coherent bosons can be viewed as a qubit stored in the ground state of the system. Our proposal provides a feasible scheme of quantum memory for storing qubits useful in quantum computation.
2. arXiv:1810.01795 (cross-list from quant-ph) [pdf, ps, other]
Phase Separation Dynamics Induced by an Interaction Quench of a Correlated Fermi-Fermi Mixture in a Double Well
J. Erdmann, S. I. Mistakidis, P. Schmelcher
Comments: 14 pages, 9 figures
Subjects: Quantum Physics (quant-ph); Quantum Gases (cond-mat.quant-gas); Atomic Physics (physics.atom-ph)
We explore the interspecies interaction quench dynamics of ultracold spin-polarized few-body mass balanced Fermi-Fermi mixtures confined in a double-well with an emphasis on the beyond Hartree-Fock correlation effects. It is shown that the ground state of particle imbalanced mixtures exhibits a symmetry breaking of the single-particle density for strong interactions in the Hartree-Fock limit, which is altered within the many-body approach. Quenching the interspecies repulsion towards the strongly interacting regime the two species phase separate within the Hartree-Fock approximation while remaining miscible in the many-body treatment. Despite their miscible character on the one-body level the two species are found to be strongly correlated and exhibit a phase separation on the two-body level that suggests the anti-ferromagnetic like behavior of the few-body mixture. For particle balanced mixtures we show that an intrawell fragmentation (filamentation) of the density occurs both for the ground state as well as upon quenching from weak to strong interactions, a result that is exclusively caused by the presence of strong correlations. Inspecting the two-body correlations a phase separation of the two species is unveiled being a precursor towards an anti-ferromagnetic state. Finally, we simulate in-situ single-shot measurements and showcase how our findings can be retrieved by averaging over a sample of single-shot images.
3. arXiv:1810.01584 (cross-list from cond-mat.stat-mech) [pdf, ps, other]
Prethermalization in the transverse-field Ising chain with long-range interactions
Takashi Mori
Comments: 24 pages, 5 figures
Subjects: Statistical Mechanics (cond-mat.stat-mech); Quantum Gases (cond-mat.quant-gas); Quantum Physics (quant-ph)
Nonequilibrium dynamics of an isolated quantum spin chain with long-range Ising interactions that decay as 1/rα (0<α<1) with the distance r is studied. It turns out that long-range interactions give rise to a big timescale separation, which causes prethermalization for all α∈(0,1). This conclusion is deduced by comparing two important timescales relevant for relaxation dynamics; one is the relaxation time of local permutation operators, which are quasi-conserved quantities in this system, and the other is the timescale of the initial relaxation due to the growth of quantum fluctuations. We also explore the entire nonequilibrium dynamics by using the discrete truncated Wigner approximation, which is consistent with the result mentioned above.
Oct. 3
1. arXiv:1810.01362 [pdf, other]
Momentum distribution and coherence of a weakly interacting Bose gas after a quench
Giovanni I. Martone, Pierre-Élie Larré, Alessandro Fabbri, Nicolas Pavloff
Comments: 23 pages, 12 figures
Subjects: Quantum Gases (cond-mat.quant-gas); General Relativity and Quantum Cosmology (gr-qc)
We consider a weakly interacting atomic Bose gas with a time-dependent nonlinear coupling constant. By developing a suitable Bogoliubov treatment we investigate the time evolution of several observables, including the momentum distribution, the degree of coherence in the system, and their dependence on dimensionality and temperature. We rigorously prove that the low-momentum Bogoliubov modes remain frozen during the whole evolution, while the high-momentum ones adiabatically follow the change in time of the interaction strength. At intermediate momenta we point out the occurrence of oscillations, which are analogous to Sakharov oscillations. We identify two wide classes of time-dependent behaviors of the coupling for which an exact solution of the problem can be found, allowing for an analytic computation of all the relevant observables. A special emphasis is put on the study of the coherence property of the system in one spatial dimension. We show that the system exhibits a smooth `light-cone effect,' with typically no prethermalization.
2. arXiv:1810.01089 [pdf, other]
Spin-charge separation effects in the low-temperature transport of 1D Fermi gases
Márton Mestyán, Bruno Bertini, Lorenzo Piroli, Pasquale Calabrese
Comments: 21 pages, 7 figures
Subjects: Quantum Gases (cond-mat.quant-gas); Statistical Mechanics (cond-mat.stat-mech); Quantum Physics (quant-ph)
We study the transport properties of a one-dimensional spinful Fermi gas, after junction of two semi-infinite sub-systems held at different temperatures. The ensuing dynamics is studied by analysing the space-time profiles of local observables emerging at large distances x and times t, as a function of ζ=x/t. At equilibrium, the system displays two distinct species of quasi-particles, naturally associated with different physical degrees of freedom. By employing the generalised hy- drodynamic approach, we show that when the temperatures are finite no notion of separation can be attributed to the quasi-particles. In this case the profiles can not be qualitatively distinguished by those associated to quasi-particles of a single species that can form bound states. On the contrary, signatures of separation emerge in the low-temperature regime, where two distinct characteristic ve- locities appear. In this regime, we analytically show that the profiles display a piece-wise constant form and can be understood in terms of two decoupled Luttinger liquids.
3. arXiv:1810.00888 [pdf, other]
Exact Strong-ETH Violating Eigenstates in the Rydberg-blockaded Atom Chain
Cheng-Ju Lin, Olexei I. Motrunich
Comments: 5.5 pages main text (including 2 figures)+5pages of appendices
Subjects: Quantum Gases (cond-mat.quant-gas); Statistical Mechanics (cond-mat.stat-mech)
A recent experiment in the Rydberg atom chain observed unusual oscillatory quench dynamics with a charge density wave initial state, and theoretical works identified a set of many-body `scar states' in the Hamiltonian as potentially responsible for the atypical dynamics. In the same nonintegrable Hamiltonian, we discover several eigenstates at infinite temperature that can be represented exactly as matrix product states with finite bond dimension, for both periodic boundary conditions (two exact E=0 states) and open boundary conditions (two E=0 states and one each E=±2‾√). This discovery explicitly demonstrates violation of strong eigenstate thermalization hypothesis in this model. These states show signatures of translational symmetry breaking with period-2 bond-centered pattern, despite being in 1d at infinite temperature. We show that the nearby many-body scar states with energies E≈±1.33 and E≈±2.66 can be well approximated as "quasiparticle excitations" on top of our exact E=0 states, and propose a quasiparticle explanation of the strong oscillations observed in experiments.
Oct. 2
1. arXiv:1810.00866 [pdf, other]
A cavity-QED simulator of slow and fast scrambling
J. Marino, A. M. Rey
Comments: 8 pages, 4 figures
Subjects: Quantum Gases (cond-mat.quant-gas); Quantum Physics (quant-ph)
We study information scrambling, as diagnosed by the out-of-time order correlations (OTOCs), in a system of large spins collectively interacting via spatially inhomogeneous and incommensurate exchange couplings. The model is realisable in a cavity QED system in the dispersive regime. Fast scrambling, signalled by an exponential growth of the OTOCs, is observed when the couplings do not factorise into the product of a pair of local interaction terms, and at the same time the state of the spins points initially coplanar to the equator of the Bloch sphere. When one of these conditions is not realised, OTOCs grow algebraically with an exponent sensitive to the orientation of the spins in the initial state. The impact of initial conditions on the scrambling dynamics is attributed to the presence of a global conserved quantity, which critically slows down the evolution for initial states close to the poles of the Bloch sphere.
2. arXiv:1810.00536 [pdf, other]
Antiferromagnetic Interorbital Spin-Exchange Interaction of 171Yb
Koki Ono, Jun Kobayashi, Yoshiki Amano, Koji Sato, Yoshiro Takahashi
Comments: 7 pages, 7 figures
Subjects: Quantum Gases (cond-mat.quant-gas)
We report on the investigation of the scattering properties between the ground state 1S0 and the metastable state 3P0 of the fermionic isotope of 171Yb. We successfully measure the s-wave scattering lengths in the two-orbital collision channels as a+eg=225(13)a0 and a−eg=355(6)a0, using the clock transition spectroscopy in a three-dimensional optical lattice. The result shows that the interorbital spin-exchange interaction is antiferromagnetic, indicating that 171Yb atom is a promising isotope for the quantum simulation of the Kondo effect with the two-orbital system.
3. arXiv:1810.00325 [pdf, other]
Exactly solvable symmetry protected topological phases of quantum spins on a zig-zag lattice
Haiyuan Zou, Erhai Zhao, Xi-Wen Guan, W. Vincent Liu
Comments: 9 pages, 6 figures
Subjects: Quantum Gases (cond-mat.quant-gas); Strongly Correlated Electrons (cond-mat.str-el); Quantum Physics (quant-ph)
A large number of symmetry protected topological phases (SPT) have been hypothesized for strongly interacting spin-1/2 systems in one dimension. The lack of simple, analytical solutions hinders deep understanding and classification. Realizing them often demands experimentally inaccessible fine-tuning. Here we show that two kinds of SPT phases natually arise in the ensemble of ultracold polar molecules confined in a zigzag optical lattice. This system, motivated by recent experiments, is described by an XXZ model whose exchange couplings can be tuned by an external field to connect several limits, previously being studied separately for spin chains and ladders. Away from the Heisenberg model limit, the ground state wave function is obtained exactly along a line and at a special point, for these two phases respectively. These exact solutions provide a clear physical picture for the SPT phases. We further complete numerically the phase diagram by using infinite time-evolving block decimation and discuss phase transitions using effective field theory.
4. arXiv:1810.00625 (cross-list from cond-mat.stat-mech) [pdf, ps, other]
Strong Eigenstate Thermalization within a Generalized Shell in Noninteracting Integrable Systems
Takashi Ishii, Takashi Mori
Comments: 5 pages
Subjects: Statistical Mechanics (cond-mat.stat-mech); Quantum Gases (cond-mat.quant-gas); Quantum Physics (quant-ph)
Integrable systems do not obey the strong eigenstate thermalization hypothesis (ETH), which has been proposed as a mechanism of thermalization in isolated quantum systems. It has been suggested that an integrable system reaches a steady state described by a generalized Gibbs ensemble (GGE) instead of thermal equilibrium. We prove that a generalized version of the strong ETH holds for noninteracting integrable systems with translation invariance. Our generalized ETH states that any pair of energy eigenstates with similar values of local conserved quantities looks similar with respect to local observables. This result tells us that an integrable system relaxes to a GGE for any initial state that has subextensive fluctuations of macroscopic local conserved quantities. Contrary to the previous derivations of the GGE, it is not necessary to assume the cluster decomposition property for an initial state.
5. arXiv:1810.00120 (cross-list from physics.atom-ph) [pdf, other]
Energy-dependent 3-body loss in 1D Bose gases
Laura A. Zundel, Joshua M. Wilson, Neel Malvania, Lin Xia, Jean-Felix Riou, David S. Weiss
Subjects: Atomic Physics (physics.atom-ph); Quantum Gases (cond-mat.quant-gas)
We study the loss of atoms in quantum Newton's cradles (QNCs) with a range of average energies and transverse confinements. We find that the three-body collision rate in one-dimension is strongly energy dependent, as predicted by a strictly 1D theory. We adapt the theory to atoms in waveguides, then using detailed momentum measurements to infer all the collisions that occur, we compare the observed loss to the adapted theory and find that they agree well.
Oct. 1
1. arXiv:1809.11071 [pdf, ps, other]
Phonon-mediated Casimir interaction between finite mass impurities
Andrei I. Pavlov, Jeroen van den Brink, Dmitri V. Efremov
Comments: 5+7 pages, 5+6 figures
Subjects: Quantum Gases (cond-mat.quant-gas); Other Condensed Matter (cond-mat.other)
The Casimir effect, a two-body interaction via vacuum fluctuations, is a fundamental property of quantum systems. In solid state physics it emerges as a long-range interaction between two impurity atoms via virtual phonons. In the classical limit for the impurity atoms in D dimensions the interaction is known to follow the universal power-law U(r)∼r−D. However, for finite masses of the impurity atoms on a lattice, it was predicted to be U(r)∼r−2D−1 at large distances. We examine how one power-law can change into another with increase of the impurity mass and in presence of an external potential. We provide the exact solution for the system in one-dimension. At large distances indeed U(r)∼r−3 for finite impurity masses, while for the infinite impurity masses or in an external potential it crosses over to U(r)∼r−1 . At short distances the Casimir interaction is not universal and depends on the impurity mass and the external potential.
2. arXiv:1809.10927 [pdf, other]
Universal Hall Response in Synthetic Dimensions
Sebastian Greschner, Michele Filippone, Thierry Giamarchi
Comments: 13 pages, 9 figures
Subjects: Quantum Gases (cond-mat.quant-gas)
We theoretically study the Hall effect on interacting M-leg ladder systems, comparing different measures and properties of the zero temperature Hall response in the limit of weak magnetic fields. Focusing on SU(M) symmetric interacting bosons and fermions, as relevant for e.g. typical synthetic dimensional quantum gas experiments, we identify an extensive regime in which the Hall imbalance ΔH is universal and corresponds to a classical Hall resistivity RH=−1/n for a large class of quantum phases. Away from this high symmetry point we observe interaction driven phenomena such as sign reversal and divergence of the Hall response.
3. arXiv:1805.01190 (cross-list from cond-mat.mes-hall) [pdf, other]
Floquet Perturbation Theory: Formalism and Application to Low-Frequency Limit
M. Rodriguez-Vega (IUB, MPI-PKS), M. Lentz (Syracuse), B. Seradjeh (IUB, MPI-PKS)
Comments: v2: 28 single-column pages, 5 figures; various typos fixed; some notation and connection to other perturbation schemes clarified; new, more descriptive title and abstract. Published version
Journal-ref: New J. Phys. 20, 093022 (2018)
Subjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Quantum Gases (cond-mat.quant-gas); Quantum Physics (quant-ph)
We develop a low-frequency perturbation theory in the extended Floquet Hilbert space of a periodically driven quantum systems, which puts the high- and low-frequency approximations to the Floquet theory on the same footing. It captures adiabatic perturbation theories recently discussed in the literature as well as diabatic deviation due to Floquet resonances. For illustration, we apply our Floquet perturbation theory to a driven two-level system as in the Schwinger-Rabi and the Landau-Zener-St\"uckelberg-Majorana models. We reproduce some known expressions for transition probabilities in a simple and systematic way and clarify and extend their regime of applicability. We then apply the theory to a periodically-driven system of fermions on the lattice and obtain the spectral properties and the low-frequency dynamics of the system.
