Dephasing in neutron interferometry

Wigner functions are used to describe various dephasing effects in neutron interferometry which are caused by thickness variations and density fluctuations of the phase shifter and by variations of the beam parameters. It will be shown that separated coherent Schrödinger-cat-like states, which exist when large phase shifts are applied, are extremely fragile and sensitive to any kind of imperfections. The related dephasing factor depends quadratically on the spatial separation of the coherent states which permits the definition of an upper limit of feasible coherent packet separation. The results show that dephasing is an unavoidable effect caused by intrinsic fluctuations inherent to any physical system.Dedicated to H. Walther on the occasion of his 60th birthday