May 2018
May 1- May 3 Biao Huang, May 4- May 8 Haiyuan Zou, May 9- May 13 Zehan Li, May 14- May 18 Jiansong Pan, May 19-May 23 Ahmet Keles, May 24- May 28 Max Aarzamazovs, May 29- May 31 Xuguang Yue
May 17 arXiv:1805.05958 (cross-list from cond-mat.str-el) [pdf, other] Universal properties of many-body localization transitions in quasiperiodic systems Shi-Xin Zhang, Hong Yao Comments: 4.5 pages plus supplemental materials, 4 figures Subjects: Strongly Correlated Electrons (cond-mat.str-el); Disordered Systems and Neural Networks (cond-mat.dis-nn); Quantum Gases (cond-mat.quant-gas); Quantum Physics (quant-ph) Precise nature of MBL transitions in both random and quasiperiodic (QP) systems remains elusive so far. In particular, whether MBL transitions in QP and random systems belong to the same universality class or two distinct ones has not been decisively resolved. Here we investigate MBL transitions in one-dimensional (d=1) QP systems as well as in random systems by state-of-the-art real-space renormalization group (RG) calculation. Our real-space RG shows that MBL transitions in 1D QP systems are characterized by the critical exponent ν≈2.4, which respects the Harris-Luck bound (ν>1/d) for QP systems. Note that ν≈2.4 for QP systems also satisfies the Harris-CCFS bound (ν>2/d) for random systems, which implies that MBL transitions in 1D QP systems are stable against weak quenched disorder since randomness is Harris irrelevant at the transition. We shall briefly discuss experimental means to measure ν of QP-induced MBL transitions. May 13 arXiv:1805.04408 [pdf, ps, other] Fidelity and criticality of quantum Ising chain with long-range interactions Zhangqi Zhu, Gaoyong Sun, Wen-Long You, Da-Ning Shi Comments: 6 pages, 5 figures Subjects: Quantum Gases (cond-mat.quant-gas) We study the criticality of long-range quantum ferromagnetic Ising chain with algebraically decaying interactions 1/rα via the fidelity susceptibility based on the exact diagonalization and the density matrix renormalization group techniques. We find that critical exponents change monotonously from the mean-field universality class to the short-range Ising universality class for intermediate α, which are consistent with recent results obtained from renormalization group. In addition, we determine the critical values for 1.8 ≤ α ≤ 3 from the finite-size scaling of the fidelity susceptibility. Our work provides very nice numerical data from the fidelity susceptibility for the quantum long-range ferromagnetic Ising chain. May 12 arXiv:1805.03153 [pdf, other] Real and imaginary energy gaps: a comparison between single excitation Superradiance and Superconductivity Nahum C. Chavez, Francesco Mattiotti, J. A. Mendez-Bermudez, Fausto Borgonovi, G. Luca Celardo Comments: 9 pages, 4 figures Subjects: Superconductivity (cond-mat.supr-con); Mesoscale and Nanoscale Physics (cond-mat.mes-hall) A comparison between the single particle spectrum of the discrete Bardeen-Cooper-Schrieffer (BCS) model, used for small superconducting grains, and the spectrum of a paradigmatic model of Single Excitation Superradiance is presented. Specifically, we study analytically the conditions under which a gapped state emerges in an equally spaced energy spectrum (Picket Fence) due to two different all-to-all couplings: a real and an imaginary one. While the former corresponds to the discrete BCS-model describing the coupling of Cooper pairs in momentum space and it induces a Superconductive regime, the latter describes the coupling of single particle energy levels to a common decay channel and it induces a Superradiant transition. We show that the transition to a Superradiant regime can be connected to the emergence of an imaginary energy gap, similarly to the transition to a Superconductive regime where a real energy gap emerges. The critical coupling at which the Superradiant gap appears is found to be independent of the system size N, in contrast with the critical coupling at which the Superconductivity gap appears, which scales as (ln N) −1 . The Superradiant and the Superconducting gaps are shown to have the same magnitude in the large gap limit. Robustness to perturbations is shown to occur even in presence of a gap in the imaginary energy axis. May 8 arXiv:1805.03073 [pdf, ps, other] Observation of a dynamical sliding phase superfluid with P-band bosons Authors: Linxiao Niu, Shengjie Jin, Xuzong Chen, Xiaopeng Li, Xiaoji Zhou Abstract: Sliding phases have been long sought-after in the context of coupled XY-models, of relevance to various many-body systems such as layered superconductors, free-standing liquid-crystal films, and cationic lipid-DNA complexes. Here we report an observation of a dynamical sliding-phase superfluid that emerges in a nonequilibrium setting from the quantum dynamics of a three-dimensional ultracold atomic gas loaded into the P-band of a one-dimensional optical lattice. A shortcut loading method is used to transfer atoms into the P-band at zero quasi-momentum within a very short time duration. The system can be viewed as a series of "pancake"-shaped atomic samples. For this far-out-of-equilibrium system, we find an intermediate time window with lifetime around tens of milliseconds, where the atomic ensemble exhibits robust superfluid phase coherence in the pancake directions, but no coherence in the lattice direction, which implies a dynamical sliding-phase superfluid. This experiment potentially opens up a novel venue to search for exotic dynamical phases by creating high-band excitations in optical lattices. May 7 arXiv:1805.02310 [pdf, other] Resonant Spin Exchange between Heteronuclear Atoms Assisted by Periodic Driving Authors: Jun-Jie Chen, Zhi-Fang Xu, Li You Abstract: We propose a general scheme for inducing resonant exchange between spins or pseudo-spins of unmatched levels via periodic driving. The basic idea is illustrated for a system of two heteronuclear atoms, for which analytical results are provided for the effective spin exchange (SE) interaction strength. It is then applied to the mixture of 23Na and 87Rb atoms with a radio-frequency (rf) or microwave field near-resonant to the mismatched Zeeman level spacings. SE interaction engineered this way is applicable to ultracold quantum gas mixtures involving spinor Bose-Bose, Bose-Fermi, and Fermi-Fermi atoms. May 4 arXiv:1805.01775 [pdf, other] Two infinite families of resonant solutions for the Gross-Pitaevskii equation Authors: Anxo Biasi, Piotr Bizon, Ben Craps, Oleg Evnin Abstract: We consider the two-dimenstional Gross-Pitaevskii equation describing a Bose-Einstein condensate in an isotropic harmonic trap. In the small coupling regime, this equation is accurately approximated over long times by the corresponding nonlinear resonant system whose structure is determined by the fully resonant spectrum of the linearized problem. We focus on two types of consistent truncations of this resonant system: first, to sets of modes of fixed angular momentum, and second, to excited Landau levels. Each of these truncations admits a set of explicit analytic solutions with initial conditions parametrized by three complex numbers. Viewed in position space, the fixed angular momentum solutions describe modulated oscillations of dark rings, while the excited Landau level solutions describe modulated precession of small arrays of vortices and antivortices. We place our findings in the context of similar results for other spatially confined nonlinear Hamiltonian systems in recent literature.
