Sep 2017
Sep 1-Sep 8 Biao Huang, Sep 9-Sep 16 Haiyuan Zou, Sep 17-Sep 24 Zehan Li, Sep 25-Sep 30 Jiansong Pan
Sep 29 arXiv:1709.10096 (cross-list from cond-mat.stat-mech) [pdf, other] Universal broadening of the light cone in low-temperature transport Bruno Bertini, Lorenzo Piroli, Pasquale Calabrese Comments: 6 pages, 3 figures Subjects: Statistical Mechanics (cond-mat.stat-mech); Quantum Gases (cond-mat.quant-gas); Quantum Physics (quant-ph) We consider the low-temperature transport properties of critical one-dimensional systems which can be described, at equilibrium, by a Luttinger liquid. We focus on the prototypical setting where two semi-infinite chains are prepared in two thermal states at small but different temperatures and suddenly joined together. At large distances x and times t, conformal field theory predicts universal profiles of the energy density and current: a single light cone emerges, resulting in a three-step form of the profiles, with sharp transitions at the edges. Here we provide a generalization to arbitrary observables, which is obtainable by taking into account the generic nonlinearity of the spectrum. Using a universal nonlinear Luttinger liquid description, we show that generic observables still display a three-step form, but smooth peaks emerge at the edges of the light cone. These are described by a universal function of ζ=x/t which we compute explicitly. In the case of interacting integrable models, we show that our predictions agree with the results of the generalized hydrodynamic approach. Sep 28 arXiv:1709.09655 (cross-list from cond-mat.str-el) [pdf, other] Effects of interaction strength, doping, and frustration on the antiferromagnetic phase of the two-dimensional Hubbard model L. Fratino, M. Charlebois, P. Sémon, G. Sordi, A.-M. S. Tremblay Comments: 6 pages, 3 figures and supplemental information Subjects: Strongly Correlated Electrons (cond-mat.str-el); Quantum Gases (cond-mat.quant-gas) Recent quantum-gas microscopy of ultracold atoms and scanning tunneling microscopy of the cuprates reveal new detailed information about doped Mott antiferromagnets, which can be compared with calculations. Using cellular dynamical mean-field theory, we map out the antiferromagnetic (AF) phase of the two-dimensional Hubbard model as a function of interaction strength U, hole doping δ and temperature T. The N\'eel phase boundary is non-monotonic as a function of U and δ. Frustration induced by second-neighbor hopping reduces N\'eel order more effectively at small U. The doped AF is stabilized at large U by kinetic energy and at small U by potential energy. The transition between the AF insulator and the doped metallic AF is continuous. At large U, we find in-gap states similar to those observed in scanning tunneling microscopy. We predict that, contrary to the Hubbard bands, these states are only slightly spin polarized. Sep 27 arXiv:1709.08934 [pdf, other] Interplay of interaction and disorder in the steady state of an open quantum system Xiansong Xu, Chu Guo, Dario Poletti Comments: 5 pages, 5 figures Subjects: Quantum Gases (cond-mat.quant-gas); Disordered Systems and Neural Networks (cond-mat.dis-nn); Quantum Physics (quant-ph) Many types of dissipative processes can be found in nature or be engineered, and their interplay with a system can give rise to interesting phases of matter. Here we study the interplay between interaction, tunneling, and disorder in the steady state of a spin chain coupled to a tailored bath. We consider a dissipation which, in contrast to disorder, tends to generate an homogeneously polarized steady state. We also find that the steady state can be highly sensitive to even weak disorder. In addition, we show that in the presence of such dissipation, even in the absence of interaction, a finite amount of disorder is needed for localization. Last, we show signatures of localization for strong disorder. In this case, small to intermediate interaction can weaken localization while strong interaction can enhance it. arXiv:1709.08794 [pdf, other] Observation of "broad" d-wave Feshbach resonances with a triplet structure Yue Cui, Chuyang Shen, Min Deng, Shen Dong, Cheng Chen, Rong Lü, Bo Gao, Meng Khoon Tey, Li You Comments: 5 pages, 3 figures. Accepted by PRL Subjects: Quantum Gases (cond-mat.quant-gas) High partial-wave (l≥2) Feshbach resonance (FR) in an ultracold mixture of 85Rb-87Rb atoms is investigated experimentally aided by a partial-wave insensitive analytic multichannel quantum-defect theory (MQDT). Two "broad" resonances from coupling between d-waves in both the open and closed channels are observed and characterized. One of them shows a fully resolved triplet structure with splitting ratio well explained by the perturbation to the closed channel due to interatomic spin-spin interaction. These tunable "broad" d-wave resonances, especially the one in the lowest-energy open channel, could find important applications in simulating d-wave coupling dominated many-body systems. In addition, we find that there is generally a time and temperature requirement, associated with tunneling through the angular momentum barrier, to establish and observe resonant coupling in nonzero partial waves. Sep 26 arXiv:1709.08484 [pdf, ps, other] Atom Pairing in Optical Superlattices J. Kangara, Chingyun Cheng, S. Pegahan, I. Arakelyan, J. E. Thomas Comments: 5 pages, 5 figures Subjects: Quantum Gases (cond-mat.quant-gas) We study the pairing of fermions in a one-dimensional lattice of tunable double-well potentials using radio-frequency spectroscopy. The spectra reveal the coexistence of two types of atom pairs with different symmetries. Our measurements are in excellent quantitative agreement with a theoretical model, obtained by extending the Green's function method of Orso et al., [Phys. Rev. Lett. 95, 060402 (2005)], to a bichromatic 1D lattice with finite harmonic radial confinement. The predicted spectra comprise hundreds of discrete transitions, with symmetry-dependent initial state populations and transition strengths. Our work provides an understanding of the elementary pairing states in a superlattice, paving the way for new studies of strongly interacting many-body systems. arXiv:1709.08457 [pdf, other] Non-adiabatic breaking of topological pumping Lorenzo Privitera, Angelo Russomanno, Roberta Citro, Giuseppe E. Santoro Subjects: Quantum Gases (cond-mat.quant-gas) We study Thouless pumping out of the adiabatic limit. Our findings show that despite its topological nature, this phenomenon is not robust to non-adiabatic effects. Indeed we find that the Floquet diagonal ensemble value of the pumped charge shows a deviation from the topologically quantized limit which is quadratic in the frequency of the driving and not exponentially small as previously believed. This is reflected also in the charge pumped in a single period, which shows a non-analytic behaviour on top of an overall quadratic decrease. We also discuss thermal effects and the experimental feasibility of observing such a deviation. Sep 25 arXiv:1709.07792 [pdf, other] Kapitza stabilization of a repulsive Bose-Einstein condensate in an oscillating optical lattice J. Martin, B. Georgeot, D. Guéry-Odelin, D. L. Shepelyansky Comments: (4+\epsilon) pages, 5 figures Subjects: Quantum Gases (cond-mat.quant-gas); Statistical Mechanics (cond-mat.stat-mech); Quantum Physics (quant-ph) We show that the Kapitza stabilization can occur in the context of nonlinear quantum fields. Through this phenomenon, an amplitude-modulated lattice can stabilize a Bose-Einstein condensate with repulsive interactions and prevent the spreading for long times. We present a classical and quantum analysis in the framework of Gross-Pitaevskii equation, specifying the parameter region where stabilization occurs. Effects of nonlinearity lead to a significant increase of stability domain comparing to the classical case. Our proposal can be experimentally implemented with current cold atom settings. Sep 23 arXiv:1704.01661 [pdf, other] Double helix nodal line superconductor Xiao-Qi Sun, Biao Lian, Shou-Cheng Zhang Comments: 9 pages, 6 figures, including Supplemental Material Subjects: Superconductivity (cond-mat.supr-con) Time-reversal invariant superconductors in three dimensions may contain nodal lines in the Brillouin zone, which behave exactly as Wilson loops of 3d momentum-space Chern-Simons theory of the Berry connection. Here we study the conditions of realizing linked nodal lines (Wilson loops), which yield a topological contribution to the thermal magnetoelectric coefficient that is given by the Chern-Simons action. We find the essential conditions are the existence of torus or higher genus fermi surfaces and spiral spin textures. We construct such a model with two torus fermi surfaces, where a generic spin-dependent interaction leads to double-helix-like linked nodal lines as the superconductivity is developed. Sep 22 arXiv:1709.07005 [pdf, ps, other] Two-dimensional conductors with interactions and disorder from particle-vortex duality Hart Goldman, Michael Mulligan, S. Raghu, Gonzalo Torroba, M. Zimet Comments: 20 pages, 2 appendices Subjects: Strongly Correlated Electrons (cond-mat.str-el); High Energy Physics - Theory (hep-th) We study Dirac fermions in two spatial dimensions (2D) coupled to strongly fluctuating U(1) gauge fields in the presence of quenched disorder. Such systems are dual to theories of free Dirac fermions, which are vortices of the original theory. In analogy to superconductivity, when these fermionic vortices localize, the original system becomes a perfect conductor, and when the vortices possess a finite conductivity, the original fermions do as well. We provide several realizations of this principle and thereby introduce new examples of strongly interacting 2D metals that evade Anderson localization Sep 19 arXiv:1709.06146 [pdf, ps, other] Metal-Insulator-Superconductor transition of spin-3/2 atoms on optical lattices Theja N. De Silva Comments: 9 pages and 6 figures Subjects: Quantum Gases (cond-mat.quant-gas) We use a slave-rotor approach within a mean-field theory to study the competition of metallic, Mott-insulating, and superconducting phases of spin-3/2 fermions subjected to a periodic optical lattice potential. In addition to the metal, the Mott-insulator, and the superconducting phase that associates with the gauge symmetry breaking of spinon field, we identify a navel emerging superconducting phase that breaks both roton and spinon field gauge symmetries. This novel superconducting phase emerges as a result of the competition between spin-0 singlet and spin-2 quintet interaction channels naturally available for spin-3/2 systems. The two superconducting phases can be distinguished from each other from quasiparticle weight. We further discuss the properties of these phases for both two-dimensional square and three-dimensional cubic lattices at zero and finite temperatures. Sep 18 arXiv:1709.05097 [pdf, ps, other] Non-stationary vortex ring in a Bose-Einstein condensate with Gaussian density Victor P. Ruban Comments: 3 pages, 3 figures Subjects: Quantum Gases (cond-mat.quant-gas); Pattern Formation and Solitons (nlin.PS) The local induction equation, approximately describing dynamics of a quantized vortex filament in a trapped Bose-Einstein condensate in the Thomas-Fermi regime on a spatially nonuniform density background ρ(r) and taking dimensionless form Rt=ϰb+[∇lnρ(R)×τ] (where ϰ is a local curvature of the filament, b is the unit binormal vector, and τ is the unit tangent vector), is shown to admit a finite-dimensional reduction if the density profile is an isotropic Gaussian, ρ∝exp(−|r|2/2). The reduction corresponds to a geometrically perfect vortex ring centered at position A(t), with orientation and size both determined by a vector B(t). Parameters A and B exhibit the same dynamics as velocity and position of a Newtonian particle do in 3D: A˙=B/|B|2−B, and B˙=A. Sep 15 arXiv:1709.04624 [pdf, other] Odd-parity topological superfluidity for fermions in a bond-centered square optical lattice Zhi-Fang Xu, Andreas Hemmerich, W. Vincent Liu Comments: 6+7 pages, 3+6 figures Subjects: Quantum Gases (cond-mat.quant-gas) We propose a physical scheme for the realization of two-dimensional topological odd-parity superfluidity in a spin-independent bond-centered square optical lattice based upon interband fermion pairing. The D4 point-group symmetry of the lattice protects a quadratic band crossing, which allows one to prepare a Fermi surface of spin-up fermions with odd parity close to the degeneracy point. In the presence of spin-down fermions with even parity populating a different energetically well separated band, odd-parity pairing is favored. Strikingly, as a necessary prerequisite for pairing both Fermi surfaces can be tuned to match well. As a result, topological superfluid phases emerge in the presence of merely s-wave interaction. Due to the Z2 symmetry of these odd-parity superfluids, we infer their topological features simply from the symmetry and the Fermi-surface topology as confirmed numerically. Sep 14 arXiv:1709.04018 [pdf, other] Drive Induced Delocalization in Aubry-André Model S. Ray, A. Ghosh, S. Sinha Subjects: Quantum Gases (cond-mat.quant-gas); Statistical Mechanics (cond-mat.stat-mech); Chaotic Dynamics (nlin.CD) Motivated by the recent experiment by Bordia et al [Nat. Phys. 13, 460 (2017)], we study single particle delocalization phenomena of Aubry-Andr\'e (AA) model subjected to periodic drives. In two distinct cases we construct an equivalent classical description to illustrate that the drive induced delocalization phenomena stems from an instability and onset of chaos in the underlying dynamics. In the first case we analyze the delocalization and the thermalization in a time modulated AA potential with respect to driving frequency and demonstrate that there exists a threshold value of the amplitude of the drive. In the next example, we show that the periodic modulation of the hopping amplitude leads to an unusual effect on delocalization with a non-monotonic dependence on the driving frequency. Within a window of such driving frequency a delocalized Floquet band with mobility edge appears, exhibiting multifractality in the spectrum as well as in the Floquet eigenfunctions. Finally, we explore the effect of interaction and discuss how the results of the present analysis can be tested experimentally. Sep 13 arXiv:1709.03704 [pdf, other] Full-counting many-particle dynamics: nonlocal and chiral propagation of correlations Yuto Ashida, Masahito Ueda Comments: 6+6 pages, 3+2 figures with full references Subjects: Quantum Gases (cond-mat.quant-gas); Statistical Mechanics (cond-mat.stat-mech); Quantum Physics (quant-ph) The ability to measure single quanta allows complete characterization of small quantum systems such as quantum dots in terms of statistics of detected signals known as full-counting statistics. Quantum gas microscopy enables one to observe many-body systems at the single-atom precision. We extend the idea of full-counting statistics to nonequilibrium open many-body dynamics and apply it to discuss the quench dynamics. By way of illustration, we consider an exactly solvable model to demonstrate the emergence of unique phenomena such as nonlocal and chiral propagation of correlations accompanying an unconventional entanglement growth. We show that these features become most prominent at the real-to-complex spectrum transition point of an underlying parity-time-symmetric effective non-Hermitian Hamiltonian. We find that correlations can propagate beyond the Lieb-Robinson bound at the cost of probabilistic nature of quantum measurement. A possible experimental realization by quantum gas microscopy is discussed. Sep 12 arXiv:1709.03021 [pdf, ps, other] Non-thermalized Steady States and Resonant Tunneling in Time-Periodically Driven Systems with Interactions Tao Qin, Walter Hofstetter Comments: 9 pages and 7 figures Subjects: Quantum Gases (cond-mat.quant-gas) Time-periodically driven systems are a versatile toolbox for realizing interesting effective Hamiltonians. Heating, caused by excitations to high-energy states, is a challenge for experiments. While most setups address the relatively weakly-interacting regime so far, it is of general interest to study heating in strongly correlated systems. Using Floquet dynamical mean-field theory, we study non-equilibrium steady states (NESS) in the Falicov-Kimball model, with time-periodically driven kinetic energy or interaction. We systematically investigate the non-thermalized properties of the NESS. For a driven kinetic energy, we show that resonant tunneling, where the interaction is an integer multiple of the driving frequency, plays an important role in the heating. In the strongly correlated regime, we show that this can be well understood using Fermi's Golden rule and the Schrieffer-Wolff transformation for a time-periodically driven system. We furthermore demonstrate that resonant tunneling can be used to control the population of Floquet states to achieve "photo-doping". For driven interactions, we find that the double occupancy is strongly modulated. Sep 11 arXiv:1709.02688 [pdf, ps, other] Topological Supersolidity of Dipolar Fermi Gases in a Spin-Dependent Optical Lattice Huan-Yu Wang, Zhen Zheng, Lin Zhuang, Wu-Ming Liu Comments: 5 pages with 6 figures Subjects: Quantum Gases (cond-mat.quant-gas) We investigate topological supersolidity of dipolar Fermi gases in a spin-dependent 2D optical lattice. Numerical results show that the topological supersolid states can be synthesized via the combination of topological superfluid states with the stripe order, where the topological superfluid states generated with dipolar interaction possess the Δx+iΔy order, and it is of D class topological classification. By adjusting the ratio between hopping amplitude tx/ty and interaction strength U with dipole orientation ϕ≈π4, the system will undergo phase transitions among the px+ipy-wave topological superfluid state, the p-wave superfluid state, and the topological supersolid state. The topological supersolid state is proved to be stable by the positive sign of the inverse compressibility. We design an experimental protocol to realize the staggered next-next-nearest-neighbour hopping via the laser assisted tunneling technique, which is the key to synthesize topological supersolid states. Sep 08 arXiv:1709.02028 [pdf, other] Observation of New Superradiant Regimes in a Bose-Einstein Condensate Ivana Dimitrova, William Lunden, Jesse Amato-Grill, Niklas Jepsen, Yichao Yu, Michael Messer, Thomas Rigaldo, Graciana Puentes,David Weld, Wolfgang Ketterle New phenomena of collective light scattering are observed when an elongated Bose-Einstein condensate is pumped by two non-interfering beams counterpropagating along its long axis. In the limit of small Rayleigh scattering rates, the presence of a second pump beam suppresses superradiance, whereas at large Rayleigh scattering rates it lowers the effective threshold power for collective light scattering. In the latter regime, the quench dynamics of the two-beam system are oscillatory, compared to monotonic in the single-beam case. In addition, the dependence on power, detuning, and atom number is explored. The observed features of the two-beam system qualitatively agree with the recent prediction of a supersolid crystalline phase of light and matter at large Rayleigh scattering rates [S. Ostermann, F. Piazza, and H. Ritsch, Phys. Rev. X 6, 021026 (2016).] arXiv:1709.02202 (cross-list from quant-ph) [pdf, other] Entanglement dynamics following a sudden quench: an exact solution Supriyo Ghosh, Kumar S. Gupta, Shashi C. L. Srivastava We present an exact, non-perturbative and fully analytical treatment of the entanglement dynamics for an isolated system of two coupled oscillators with time dependent frequency and coupling. The entanglement dynamics is analyzed following a sudden quench of the system parameters. We have obtained the solutions of the time dependent Schrodinger's equation (TDSE) for the system of two coupled oscillators under an arbitrary sudden quench. Using this solution, we are led to the exact analytical expressions for the time dependent Renyi and von Neumann entropies which are fully consistent with the TDSE. The two site Bose-Hubbard model in the tunneling regime is equivalent to this system. Our analysis thus predicts the patterns of time evolution of the entanglement entropies in the two site Bose-Hubbard model, which is amenable to empirical realization in cold atom systems. arXiv:1709.01942 [pdf, ps, other] Scale invariance in integrable quantum oscillators' long-time dynamics Emanuele G. Dalla Torre (Submitted on 6 Sep 2017) Scale invariance usually occurs in extended systems where correlation functions decay algebraically in space and/or time. Here we introduce a new type of scale invariance, occurring in distribution functions of physical observables. At equilibrium, these functions decay over a typical scale set by the temperature, but they can become scale invariant in a sudden quantum quench. We exemplify this effect through the analysis of an integrable quantum oscillator, and show that the associated critical exponent is universal. Our study opens the possibility to address integrability and its breaking in distribution functions, and has immediate applications to matter-wave interferometers. Sep 07 arXiv:1709.01830 [pdf, other] ℤ2 topological insulator analog for vortices in an interacting bosonic quantum fluid O. Bleu, G. Malpuech, D. D. Solnyshkov ℤ2 topological insulators for photons and in general bosons cannot be strictly implemented because of the lack of symmetry-protected pseudospins. We show that the required protection can be provided by the real-space topological excitation of an interacting quantum fluid: quantum vortex. We consider a Bose-Einstein Condensate at the Γ point of the Brillouin zone of a quantum valley Hall system based on two staggered honeycomb lattices. We demonstrate the existence of a coupling between the winding number of a vortex and the valley of the bulk Bloch band. This leads to chiral vortex propagation at the zigzag interface between two regions of inverted staggering, where the winding-valley coupling provides true topological protection against backscattering, contrary to the interface states of the non-interacting Hamiltonian. This configuration is an analog of a ℤ2 topological insulator for quantum vortices. Sep 05 Characterizing topology by dynamics: Chern number from linking number Matthias Tarnowski, F. Nur Ünal, Nick Fläschner, Benno S. Rem, André Eckardt, Klaus Sengstock, Christof Weitenberg Topology plays an important role in modern solid state physics describing intriguing quantum states such as topological insulators. It is an intrinsically non-local property and therefore challenging to access, often studied only via the resulting edge states. Here, we measure the topological index directly from the far-from-equilibrium dynamics of the bulk. We use the mapping of the Chern number to the linking number of dynamical vortex trajectories appearing after a quench to the Hamiltonian of interest. We thereby map out the topological phase diagram of quantum gases in optical lattices via a purely dynamical response. Such relations between two topological indices in static and dynamical properties could be also an important approach for exploring topology in the case of interactions. arXiv:1709.01046 [pdf, other] Characterizing topology by dynamics: Chern number from linking number Matthias Tarnowski, F. Nur Ünal, Nick Fläschner, Benno S. Rem, André Eckardt, Klaus Sengstock, Christof Weitenberg Topology plays an important role in modern solid state physics describing intriguing quantum states such as topological insulators. It is an intrinsically non-local property and therefore challenging to access, often studied only via the resulting edge states. Here, we measure the topological index directly from the far-from-equilibrium dynamics of the bulk. We use the mapping of the Chern number to the linking number of dynamical vortex trajectories appearing after a quench to the Hamiltonian of interest. We thereby map out the topological phase diagram of quantum gases in optical lattices via a purely dynamical response. Such relations between two topological indices in static and dynamical properties could be also an important approach for exploring topology in the case of interactions.
