Observable frequency shifts via spin-rotation coupling

TL;DR

This paper explores the phase perturbation caused by spin-rotation coupling, extending the Sagnac effect, and discusses experimental evidence and proposals for detecting frequency shifts in photons and neutrons due to this coupling.

Contribution

It introduces a theoretical framework for spin-rotation coupling effects and proposes neutron interferometry experiments to empirically verify photon and fermion frequency shifts.

Findings

Circularly polarized light frequency shifts twice the rotation rate.

Experimental interpretation supports spin-rotation coupling in photons.

Proposed neutron interferometry experiment to detect analogous effects.

Abstract

The phase perturbation arising from spin-rotation coupling is developed as a natural extension of the celebrated Sagnac effect. Experimental evidence in support of this phase shift, however, has yet to be realized due to the exceptional sensitivity required. We draw attention to the relevance of a series of experiments establishing that circularly polarized light, upon passing through a rotating half-wave plate, is changed in frequency by twice the rotation rate. These experiments may be interpreted as demonstrating the role of spin-rotation coupling in inducing this frequency shift, thus providing direct empirical verification of the coupling of the photon helicity to rotation. A neutron interferometry experiment is proposed which would be sensitive to an analogous frequency shift for fermions. In this arrangement, polarized neutrons enter an interferometer containing two spin flippers, one of which is rotating while the other is held stationary. An observable beating in the transmitted neutron beam intensity is predicted.