Which-Way Information in Double-Slit and COW Experiments with Unstable Particles

TL;DR

This paper investigates how unstable particles in quantum interference experiments provide inherent which-way information, reducing interference contrast and illustrating a duality between path predictability and visibility.

Contribution

It demonstrates that unstable particles introduce a priori which-way information in double-slit and COW experiments, affecting interference patterns unlike stable particles.

Findings

Unstable particles cause a loss of interference contrast.

A priori path predictability relates to visibility via a duality relation.

Interference contrast decreases with particle instability.

Abstract

One might expect that a quantum undecayed unstable particle (QUUP) should behave in the same manner as an identical, albeit stable, particle, but it turns out that this is not always true. We show explicitly that using QUUPs in the double-slit and Colella-Overhauser-Werner (COW) experiments leads to a priori which-way information that creates a loss of interference contrast when compared to the same experiments performed using stable particles. In both of these cases, a priori path predictability ${\cal P}$ is related to the interference visibility ${\cal V}$ by the duality relation ${\cal P}^{2} + {\cal V}^{2} = 1$.