Separating a particle's mass from its momentum

TL;DR

This paper generalizes the Quantum Cheshire Cat effect to massive particles, demonstrating that mass and momentum can be separated spatially using weak measurements, with implications for quantum interpretation debates.

Contribution

It introduces a new generalization of the Quantum Cheshire Cat effect applicable to any massive particle, independent of spin or charge, and discusses its controversial interpretation.

Findings

Mass and momentum can be spatially separated in massive particles.

A gedanken experiment illustrates the effect using moving interferometers.

The interpretation of the effect remains highly debated.

Abstract

The Quantum Cheshire Cat experiment showed that when weak measurements are performed on pre- and post-selected system, the counterintuitive result has been obtained that a neutron is measured to be in one place without its spin, and its spin is measured to be in another place without the neutron. A generalization of this effect is presented with a massive particle whose mass is measured to be in one place with no momentum, while the momentum is measured to be in another place without the mass. The new result applies to any massive particle, independent of its spin or charge. A gedanken experiment which illustrates this effect is presented using a nested pair of Mach-Zehnder interferometers, but with some of the mirrors and beam splitters moving relative to the laboratory frame. The titular interpretation of this experiment is extremely controversial, and rests on several assumptions, which are discussed in detail. An alternative interpretation using the counterparticle model of Aharonov et al. is also discussed.