Physically significant phase shifts in matter-wave interferometry

TL;DR

This paper explores the physical meaning of phase shifts in matter-wave interferometers, showing how they relate to classical measurements in low-order potentials and reveal uniquely quantum information in high-order potentials.

Contribution

It provides a conceptual analysis through thought experiments, clarifying when matter-wave phases reflect classical information versus quantum-specific effects.

Findings

In low-order potentials, phase equals classical position measurement information.

In high-order potentials, phase contains non-classical information.

High-order potential phases are fundamentally different from classical measurement signals.

Abstract

Many different formalisms exist for computing the phase of a matter-wave interferometer. However, it can be challenging to develop physical intuition about what a particular interferometer is actually measuring or about whether a given classical measurement provides equivalent information. Here we investigate the physical content of the interferometer phase through a series of thought experiments. In low-order potentials, a matter-wave interferometer with a single internal state provides the same information as a sum of position measurements of a classical test object. In high-order potentials, the interferometer phase becomes decoupled from the motion of the interferometer arms, and the phase contains information that cannot be obtained by any set of position measurements on the interferometer trajectory. This phase shift in a high-order potential fundamentally distinguishes matter-wave interferometers from classical measuring devices.