Dr. Chiao has proposed an innovative experiment to test the quantum mechanical nature of a phase factor in the quantum wave equation whose existence was recently predicted by M.V. Berry of Bristol U. This phase factor is acquired by a quantum system upon its adiabatic transport around a closed circuit in parameter space, & is a topological property of the circuit. Dr. Chiao & collaborators recently carried out an optical demonstration of the Berry phase in the classical limit using polarization rotation in a helically-wound optical fiber. The excitement of these experiments, which were recently published in Physical Review Letters, was captured in an extensive news article in the 9/18/86 issue of Nature. There is currently considerable controversy that the observed phase shifts are purely classical in nature. A test of the quantum nature of the phase through proposed fiber-optic interferometry in the singly photon limit could establish a novel correspondence between classical and quantum mechanics. The photon as a particle with spin could acquire a topologically nontrivial history dependence of its phase. Chiao points out several potential novel applications arising from the Berry phase, such as, in gyroscopy where this new type of optical activity could be exploited to detect rotations with respect to a fixed inertial frame in space.
