Detecting quantum backflow by the density of a Bose-Einstein Condensate

TL;DR

This paper proposes a method to detect quantum backflow, a quantum phenomenon, by measuring particle density in Bose-Einstein condensates, enabling experimental observation with current technology.

Contribution

It establishes a relation between quantum backflow and particle density, and introduces a practical scheme using Bose-Einstein condensates for experimental detection.

Findings

Derived a relation linking backflow to particle density.

Proposed an experimental scheme with Bose-Einstein condensates.

Showed that a positive momentum kick can induce negative current flow.

Abstract

Quantum backflow is a classically forbidden effect consisting in a negative flux for states with negligible negative momentum components. It has never been observed experimentally so far. We derive a general relation that connects backflow with a critical value of the particle density, paving the way for the detection of backflow by a density measurement. To this end, we propose an explicit scheme with Bose-Einstein condensates, at reach with current experimental technologies. Remarkably, the application of a positive momentum kick, via a Bragg pulse, to a condensate with a positive velocity may cause a current flow in the negative direction.