Proposed neutron interferometry test of Berry's phase for a circulating planar spin

TL;DR

This paper proposes an experimental neutron interferometry setup to measure the Berry phase acquired by a spin-1/2 particle moving in a plane under a magnetic field, demonstrating topological quantum effects.

Contribution

It introduces a novel neutron interferometry experiment to detect Berry's phase in a circulating planar spin system induced by a perpendicular magnetic wire.

Findings

Predicted destructive interference due to Berry phase

Feasibility of measuring Berry's phase with neutron interferometry

Potential to observe topological quantum effects in spin systems

Abstract

The energy eigenstates of a spin$-\frac{1}{2}$ particle in a magnetic field confined to a plane, define a planar spin. If the particle moves adiabatically around a loop in this plane, it picks up a topological Berry phase that can only be an integer multiple of $\pi$. We propose a neutron interferometry test of the Berry phase for a circulating planar spin induced by a magnetic field caused by a very long current-carrying straight wire perpendicular to the plane. This Berry phase causes destructive interference in the direction of the incoming beam of thermal neutrons moving through a triple-Laue interferometer.