The interference of polarized light as an early example of Berry's phase

Abstract

The term "Berry's phase" is now commonly used to describe the change in the phase of a quantum state vector under a sequence of adiabatic changes which returns the system to its original state. The purpose of this note is to point out that a particular case of this concept, as applied to the interference of polarized light, was studied both theoretically and experimentally in a series of papers published in the fifties by S. Pancharatnam. The phase term is proportional to a solid angle on the Poincare sphere which represents the states of polarization of light.