Quantum backflow effect and nonclassicality

TL;DR

This paper investigates the quantum backflow effect, revealing it as a distinct form of nonclassicality that is more restrictive than Wigner function negativity, with implications for understanding quantum behavior and noise effects.

Contribution

It clarifies the relationship between quantum backflow and nonclassicality, showing backflow as a more restrictive nonclassical feature than Wigner negativity.

Findings

Backflow linked to a stricter nonclassicality than Wigner negativity.

Wigner negativity is necessary but not sufficient for backflow.

Thermal noise more easily destroys backflow than Wigner negativity.

Abstract

The quantum backflow effect is a counterintuitive behavior of the probability current of a free particle, which may be negative even for states with vanishing negative momentum component. Here we address the notion of nonclassicality arising from the backflow effect, i.e. from the negativity of the probability current, and analyze its relationships with the notion of nonclassicality based on the negativity of the Wigner function. Our results suggest that backflow is linked to a different, and in fact more restrictive, notion of nonclassicality, the negativity of the Wigner function being only a necessary prerequisite for its occurrence. This hierarchical structure may be confirmed by looking at the addition of thermal noise, which more easily destroys the negativity of the probability current than the negativity of the Wigner function itself.