Arxiv Selection Aug 2019

Aug 1-Aug 7 Zehan Li, Aug 8- Aug 14 Jiansong Pan, Aug 15- Aug 21 Ahmet Keles, Aug 22 - Aug 28 Haiping Hu

Aug 1

arXiv:1907.12566 (cross-list from cond-mat.mes-hall) [pdf, other]

Observation of non-Hermitian bulk-boundary correspondence in quantum dynamics

Lei Xiao, Tianshu Deng, Kunkun Wang, Gaoyan Zhu, Zhong Wang, Wei Yi, Peng Xue

Comments: 15 pages, 9 figures

Subjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Quantum Gases (cond-mat.quant-gas); Strongly Correlated Electrons (cond-mat.str-el); Optics (physics.optics); Quantum Physics (quant-ph)

Bulk-boundary correspondence, a central principle in topological matter relating bulk topological invariants to edge states, breaks down in a generic class of nonHermitian systems that have so far eluded experimental effort. Here we theoretically predict and experimentally observe non-Hermitian bulk-boundary correspondence, a fundamental generalization of the conventional bulk-boundary correspondence, in discrete-time non-unitary quantum-walk dynamics of single photons. We experimentally demonstrate photon localizations near boundaries even in the absence of topological edge states, thus confirming the non-Hermitian skin effect. Facilitated by our experimental scheme of edge-state reconstruction, we directly measure topological edge states, which match excellently with non-Bloch topological invariants calculated from localized bulk-state wave functions. Our work unequivocally establishes the non-Hermitian bulk-boundary correspondence as a general principle underlying non-Hermitian topological systems, and paves the way for a complete understanding of topological matter in open systems.

Aug 2

arXiv:1908.00108 [pdf, other]

Strongly correlated quantum droplets in quasi-1D dipolar Bose gas

Rafał Ołdziejewski, Wojciech Górecki, Krzysztof Pawłowski, Kazimierz Rzążewski

Comments: 9 pages, 4 figures, comments welcome

Subjects: Quantum Gases (cond-mat.quant-gas); Quantum Physics (quant-ph)

We exploit a few- to many-body approach to study strongly interacting dipolar bosons in the quasi-one-dimensional system. The dipoles attract each other while the short range interactions are repulsive. Solving numerically exactly the multi-atom Schrödinger equation, we discover that such systems can exhibit not only the well known bright soliton solutions but also novel quantum droplets for a strongly coupled case. For larger systems, basing on microscopic properties of the found few-body solution, we propose a new generalization of the Gross-Pitaevskii equation (GPE) that incorporates the Lieb-Liniger energy in a local density approximation. Not only does such a framework provide an alternative mechanism of the droplet stability, but it also introduces means to further analyze this previously unexplored quantum phase. In the limiting strong repulsion case, yet another simple multi-atom model is proposed. We stress that the celebrated Lee-Huang-Yang term in the GPE is not applicable in this case.

Aug 5

arXiv:1908.00761 [pdf, other]

Observation of Quantum Droplets in a Heteronuclear Bosonic Mixture

C. D'Errico, A. Burchianti, M. Prevedelli, L. Salasnich, F. Ancilotto, M. Modugno, F. Minardi, C. Fort

Comments: 9 pages, 7 figures

Subjects: Quantum Gases (cond-mat.quant-gas)

We show that the Lee-Huang-Yang (LHY) energy functional for a heteronuclear Bose mixture can be accurately approximated by an expression that has the same functional form as in the homonuclear case. It is characterized by two exponents, which can be treated as fitting parameters. We demonstrate that the values of these parameters which preserve the invariance under permutation of the two atomic species are exactly those of the homonuclear case. Deviations from the actual expression of LHY energy functional are discussed quantitatively.

Aug 9

arXiv:1908.02821 [pdf, other]

Integrable model of a p-wave bosonic superfluid

Sergio Lerma-Hernandez, Jorge Dukelsky, Gerardo Ortiz

Subjects: Quantum Gases (cond-mat.quant-gas); Mathematical Physics (math-ph); Quantum Physics (quant-ph)

We present an exactly-solvable p-wave pairing model for two bosonic species. The model is solvable in any dimension and it shows striking similarities with the p+ip Richardson-Gaudin fermionic model. As the fermionic model, our bosonic counterpart displays a third order quantum phase transition separating a fragmented singlet pair condensate from a pair Bose superfluid. At criticality the exact eigenstate is a pair condensate analogous to the fermionic Moore-Read state.

Aug 12

arXiv:1908.03470 [pdf, other]

Quantum fluctuations beyond the Gutzwiller approximation in the Bose-Hubbard model

F. Caleffi, M. Capone, C. Menotti, I. Carusotto, A. Recati

Comments: 6 pages, 3 figures

Subjects: Quantum Gases (cond-mat.quant-gas); Strongly Correlated Electrons (cond-mat.str-el); Superconductivity (cond-mat.supr-con)

We develop a quantum many-body theory of the Bose-Hubbard model based on the canonical quantization of the action derived from a Gutzwiller mean-field ansatz. Capitalizing on the ability of this latter to describe both the Mott insulator and the superfluid phases, our theory is a systematic generalization of the Bogoliubov theory of weakly interacting gases and provides accurate results across the whole phase diagram. We characterize the superfluid-insulator phase transition studying the two-point correlation functions, the local number fluctuations, and the superfluid stiffness across the whole phase diagram. Two different universality classes are recovered at integer and non-integer filling and the density fluctuations are successfully compared to accurate quantum Monte Carlo data. To conclude we highlight the potential of our theory in view of including interactions between collective modes to describe their finite lifetime and their quantum optical properties.

Aug 13

arXiv:1908.04100 (cross-list from cond-mat.mes-hall) [pdf, other]

Floquet engineering of topological phases protected by emergent symmetries under resonant drives

Kaoru Mizuta, Kazuaki takasan, Norio Kawakami

Comments: 13 pages, 6 figures

Subjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Quantum Gases (cond-mat.quant-gas)

Floquet engineering is one of the most vigorous fields in periodically driven (Floquet) systems, with which we can control phases of matter usually by high-frequency drives. In this paper, with Floquet engineering by a combination of high-frequency drives and resonant drives, we propose a way to realize nontrivial topological phases protected by a Z2×Z2 symmetry only in the presence of a Z2 symmetry, using a robust emergent Z2 symmetry induced by the resonant drives. Moreover, the symmetry protected topological (SPT) phases are switchable between nontrivial and trivial phases only by the direction of a static transverse field, and even perturbations on the resonant drive can be utilized to realize richer SPT phases. We also discuss the real-time dynamics of the model, and find that which topological phases the system lies in can be distinguished by a period doubling of a nonlocal order parameter, as with discrete time crystals. A realization or a control of nontrivial SPT phases without the required symmetries by resonant drives, proposed in this paper, would shed a new light on the observation of topological phenomena in nonequilibrium setups.

arXiv:1908.03868 [pdf, other]

Many-body dynamical localization and thermalization

Christine Khripkov, Amichay Vardi, Doron Cohen

Comments: 9 pages, 7 figures

Subjects: Quantum Gases (cond-mat.quant-gas); Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Statistical Mechanics (cond-mat.stat-mech)

We demonstrate dynamical localization in a generic setup of two weakly-coupled chaotic subsystems. The minimal subsystem of experimental interest is a 3-mode Bose-Hubbard trimer. We clarify the procedure for identification of a mobility edge in the chaotic sea, beyond which dynamical localization suppresses ergodization, and hence arrests the thermalization process.

arXiv:1908.04134 [pdf, other]

Frustrated Quantum Magnetism with Bose Gases in Triangular Optical Lattices at Negative Absolute Temperatures

Daisuke Yamamoto, Takeshi Fukuhara, Ippei Danshita

Comments: 6+5 pages, 4+5 figures

Subjects: Quantum Gases (cond-mat.quant-gas); Strongly Correlated Electrons (cond-mat.str-el)

We propose an experimental protocol to perform analog quantum simulation of frustrated antiferromagnetism with strong quantum fluctuations by using ultracold Bose gases in triangular optical lattices with isosceles anisotoropy of hoppings. Specifically, we combine a phase-imprinting scheme with sudden sign inversion of the interatomic interaction and the trap potential to prepare a chiral superfluid state with a negative absolute temperature. In the framework of the time-dependent Gutzwiller approach, we compute the time evolution of the state subjected to a slow sweep of the hopping energy. We show that in this process the system simulates a state near equilibrium of the Bose-Hubbard model with sign-inverted hoppings. By means of the cluster mean-field method with a cluster size scaling, we quantitatively predict the quantum critical point of the superfluid-Mott insulator transition as a function of the spatial anisotropy parameter, which serves as a benchmark for quantum simulation.