Quantum phase shift caused by spatial confinement

This paper presents the results of optical interferometry experiments ill w hich the phase of photons ill one arm of a Mach-Zehnder interferometer is m odified by applying a transverse constriction. An equivalent quanthum inter ferometry experiment ment using neutron, de Broglie waves is discussed in w hich the observed;phase shift is in the spirit of the force-free phase shif t of rile Aharonov-Bohm effects. In the optical experiments the experimenta l, results are in excellent agreement with predictions.