Arxiv Selection April 2019

April 1-April 7 Biao Huang, April 8-April 14 Sayan Choudhury, April 15-April 21 Zehan Li, April 22- April 28 Jiansong Pan

Apr 16

arXiv:1904.07009 [pdf, other]

Exactly solvable model of two interacting Rydberg-dressed atoms confined in a two-dimensional harmonic trap

Przemysław Kościk, Tomas Sowiński

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

Exactly solvable model of two Rydberg-dressed atoms moving in a quasi-two-dimensional harmonic trap is introduced and its properties are investigated. Depending on the strength of inter-particle interactions and the critical range of the potential, the two-particle eigenstates are classified with respect to the excitations of the center-of-mass motion, relative angular momentum, and relative distance variable. Having these solutions in hand, we discuss inter-particle correlations as functions of interaction parameters. We also present a straightforward prescription of how to generalize obtained solutions to higher dimensions.

Apr 15

arXiv:1904.06208 [pdf, other]

Quench induced vortex-bright-soliton formation in binary Bose-Einstein condensates

K. Mukherjee, S. I. Mistakidis, P. G. Kevrekidis, P. Schmelcher

Comments: 16 pages, 10 figures

Subjects: Quantum Gases (cond-mat.quant-gas); Pattern Formation and Solitons (nlin.PS); Atomic Physics (physics.atom-ph); Quantum Physics (quant-ph)

We unravel the spontaneous generation of vortex-bright-soliton structures in binary Bose-Einstein condensates confined in a two-dimensional harmonic trap where one of the two species has been segmented into two parts by a potential barrier. To trigger the dynamics the potential barrier is suddenly removed and subsequently the segments perform a counterflow dynamics. We consider a relative phase difference of π between the segments, while a singly quantized or no vortex is imprinted at the center of the other species. The number of vortex structures developed within the segmented species after the merging of its segments is found to depend on the potential presence of the initial vortex on the other species. In particular, a π phase difference in the segmented species and a vortex in the other species result in a single vortex-bright-soliton structure. However, when the non-segmented species does not contain a vortex the counterflow dynamics of the segmented species gives rise to a vortex dipole in it accompanied by two bright solitary waves arising in the non-segmented species. Inspecting the dynamics of the angular momentum we show that it can be transferred from one species to the other, and its transfer rate can be tuned by the strength of the interspecies interactions.

Apr 3

arXiv:1904.01026

Dicke time crystals in driven-dissipative quantum many-body systems

Bihui Zhu, Jamir Marino, Norman Y. Yao, Mikhail D. Lukin, Eugene A. Demler

The Dicke model -- a paradigmatic example of superradiance in quantum optics -- describes an ensemble of atoms which are collectively coupled to a leaky cavity mode. As a result of the cooperative nature of these interactions, the system's dynamics are captured by the behavior of a single mean-field, collective spin. In this mean-field limit, it has recently been shown that the interplay between photon losses and periodic driving of light-matter coupling can lead to time-crystalline-like behavior of the collective spin. In this work, we investigate whether such a Dicke time crystal is stable to perturbations that explicitly break the mean-field solvability of the conventional Dicke model. In particular, we consider the addition of short-range interactions between atoms, which breaks the collective coupling and leads to complex many-body dynamics. In this context, the interplay between periodic driving, dissipation and interactions yields a rich set of dynamical responses including long-lived and metastable Dicke time crystals, where losses can cool down the many-body heating resulting from the continuous pump of energy from the periodic drive. Specifically, when the additional short-range interactions are ferromagnetic, we observe time crystalline behavior at non-perturbative values of the coupling strength, suggesting the possible existence of stable dynamical order in a driven-dissipative quantum many-body system. These findings illustrate the rich nature of novel dynamical responses with many-body character in quantum optics platforms.

arXiv:1904.01039

Anomalous relaxation and the high-temperature structure factor of XXZ spin chains

Sarang Gopalakrishnan, Romain Vasseur, Brayden Ware

We compute the spin structure factor of XXZ spin chains in the Heisenberg and gapped (Ising) regimes in the high-temperature limit for nonzero magnetization, within the framework of generalized hydrodynamics including diffusive corrections. The structure factor shows a hierarchy of timescales in the gapped phase, owing to s-spin magnon bound states (`strings') of various sizes. Although short strings move ballistically, long strings move primarily diffusively as a result of their collisions with short strings. The interplay between these effects gives rise to anomalous power-law decay of the spin structure factor, with continuously varying exponents, at any fixed separation in the late-time limit. We elucidate the crossover to diffusion (in the gapped phase) and to superdiffusion (at the isotropic point) in the half-filling limit. We verify our results via extensive matrix product operator calculations.

Apr 1

arXiv:1904.00465

Superfluid Vortex Dynamics on Planar Sectors and Cones

Pietro Massignan, Alexander L. Fetter

We study the dynamics of vortices formed in a superfluid film adsorbed on the curved two-dimensional surface of a cone. To this aim, we observe that a cone can be unrolled to a sector on a plane with periodic boundary conditions on the straight sides. The sector can then be mapped conformally to the whole plane, leading to the relevant stream function. In this way, we show that a superfluid vortex on the cone precesses uniformly at fixed distance from the apex. The stream function also yields directly the interaction energy of two vortices on the cone. We then study the vortex dynamics on unbounded and bounded cones. In suitable limits, we recover the known results for dynamics on cylinders and planar annuli.