Quantum backflow in a ring

TL;DR

This paper demonstrates that quantum backflow, a counterintuitive quantum effect where probability current is negative despite non-negative momenta, is enhanced when a particle moves in a circular ring, making experimental observation more feasible.

Contribution

The study shows that constraining a quantum particle to a ring amplifies the backflow effect, providing a new approach for experimental detection of this fragile quantum phenomenon.

Findings

Quantum backflow is more pronounced on a ring.

Enhanced backflow improves prospects for experimental observation.

The effect remains weak and fragile in linear motion.

Abstract

Free motion of a quantum particle with the wave function entirely comprised of plane waves with non-negative momenta may be accompanied by negative probability current, an effect called quantum backflow. The effect is weak and fragile, and has not yet been observed experimentally. Here we show that quantum backflow becomes significantly more pronounced and more amenable to experimental observation if, instead of letting the particle move along a straight line, one forces it to move in a circular ring.