Quantum Monte Carlo simulation of BEC-impurity tunneling

TL;DR

This paper introduces a novel quantum-tunneling Monte Carlo method that effectively simulates impurity tunneling in a Bose-Einstein condensate, revealing two quasi-particle tunneling regimes and their dependence on coupling strength.

Contribution

The paper presents a new QTMC method that overcomes standard Monte Carlo limitations and applies it to impurity tunneling in BECs, uncovering distinct quasi-particle peaks.

Findings

Identification of phonon-assisted tunneling and self-trapping peaks.

Observation of spectral shifts with increasing coupling.

Analysis of effective mass changes of quasi-particles.

Abstract

Polaron tunneling is a prominent example of a problem characterized by different energy scales, for which the standard quantum Monte Carlo methods face a slowdown problem. We propose a new quantum-tunneling Monte Carlo (QTMC) method which is free from this issue and can be used for a wide range of tunneling phenomena. We apply it to study an impurity interacting with a one-dimensional Bose-Einstein condensate and simultaneously trapped in an external double-well potential. Our scheme works for an arbitrary coupling between the particle and condensate and, at the same time, allows for an account of tunneling effects. We discover two distinct quasi-particle peaks associated, respectively, with the phonon-assisted tunneling and the self-trapping of the impurity, which are in a crossover regime for the system modeled. We observe and analyze changes in the weights and spectral positions of the peaks (or, equally, effective masses of the quasi-particles) when the coupling strength is increased. Possible experimental realizations using cold atoms are discussed.