Arxiv Selection Apr 2020

Apr 1- Apr 7 Bhaskar Mukherjee, Apr 8- Apr 14 Zehan Li, Apr 15- Apr 21 Haiping Hu, Apr 22- Apr 28 Sayan Choudhury

Apr 9

arXiv:2004.03823 [pdf, other]

Static kinks in chains of interacting atoms

Haggai Landa, Cecilia Cormick, Giovanna Morigi

Comments: 7 pages, 3 figures

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

We theoretically analyse the equation of topological solitons in a chain of particles interacting via a repulsive power-law potential and confined by a periodic lattice. Starting from the discrete model, we perform a gradient expansion which delivers the kink equation in the continuum limit. The power-law interaction modifies the sine-Gordon equation, giving rise to a rescaling of the coefficient in from of the second derivative (the kink width) and to an additional integral term. We argue that the integral term does not affect the local properties of the kink, but it governs the behaviour at the asymptotics. The kink behaviour at the center is dominated by a sine-Gordon equation, where the kink width tends to increase with the power law exponent. When the interaction is the Coulomb repulsion, in particular, the kink width depends logarithmically on the chain size. We define an appropriate thermodynamic limit and compare our results with existing studies performed for infinite chains. Our formalism allows one to systematically take into account the finite-size effects and also slowly varying external potentials, such as for instance the curvature in an ion trap.

Apr 10

arXiv:2004.04200 [pdf, other]

Creating solitons with controllable and near zero velocity in Bose-Einstein condensates

A. R. Fritsch, Mingwu Lu, G. H. Reid, A. M. Piñeiro, I. B. Spielman

Comments: 10 pages, 6 figures

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

Established techniques for deterministically creating dark solitons in repulsively interacting atomic Bose-Einstein condensates (BECs) can only access a narrow range of soliton velocities. Because velocity affects the stability of individual solitons and the properties of soliton-soliton interactions, this technical limitation has hindered experimental progress. Here we create dark solitons in highly anisotropic cigar-shaped BECs with arbitrary position and velocity by simultaneously engineering the amplitude and phase of the condensate wavefunction, improving upon previous techniques which only explicitly manipulated the condensate phase. The single dark soliton solution present in true 1D systems corresponds to the kink soliton in anisotropic 3D systems and is joined by a host of additional dark solitons including vortex ring and solitonic vortex solutions. We readily create dark solitons with speeds from zero to half the sound speed. The observed soliton oscillation frequency suggests that we imprinted solitonic vortices, which for our cigar-shaped system are the only stable solitons expected for these velocities. Our numerical simulations of 1D BECs show this technique to be equally effective for creating kink solitons when they are stable. We demonstrate the utility of this technique by deterministically colliding dark solitons with domain walls in two-component spinor BECs.

Apr 13

arXiv:2004.05014 [pdf, other]

Emergence of a pseudogap in the BCS-BEC crossover

Adam Richie-Halford, Joaquín E. Drut, Aurel Bulgac

Comments: 6 pages (including references), 4 figures

Subjects: Quantum Gases (cond-mat.quant-gas); Superconductivity (cond-mat.supr-con); Nuclear Theory (nucl-th)

Strongly correlated Fermi systems with pairing interactions become superfluid below a critical temperature Tc. The extent to which such pairing correlations alter the behavior of the liquid at temperatures T > Tc is a subtle issue that remains an area of debate, in particular regarding the appearance of the so-called pseudogap in the BCS–BEC crossover of unpolarized spin-1/2 nonrel- ativistic matter. To shed light on this, we extract several quantities of crucial importance at and around the unitary limit, namely: the odd-even staggering of the total energy, the spin susceptibil- ity, the pairing correlation function, the condensate fraction, and the critical temperature Tc, using a non-perturbative, constrained-ensemble quantum Monte Carlo algorithm.

Apr 14

arXiv:2004.05737 [pdf, other]

Quantum droplet in a mixture of Bose-Fermi superfluids

Jing-Bo Wang, Jian-Song Pan, Xiaoling Cui, Wei Yi

Comments: 7 pages, 5 figures

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

We study the formation of quantum droplets in the mixture of a single-component Bose-Einstein condensate (BEC), and a two-species Fermi superfluid across a wide Feshbach resonance. With repulsive boson-boson and attractive boson-fermion interactions, we show that quantum droplets can be stabilized by attractive fermion-fermion interactions in the Bardeen-Cooper-Schieffer (BCS) side of the resonance, and can also exist in deep BEC regime under weak boson-fermion interactions. We map out the phase diagram for stable droplets with respect to the boson-boson and boson-fermion interactions, and discuss the role of different types of quantum fluctuations in the relevant regions of the BCS-BEC crossover. Our work reveals the impact of fermion pairing on the formation of quantum droplets in Bose-Fermi mixtures, and provides a useful guide for future experiments.