Quantum neutron optics

The invention of neutron interferometry in 1974 stimulated many experiments related to the wave-particle dualism of quantum mechanics. Widely separated coherent beams can be produced within a perfect crystal interferometer which can be influenced by nuclear, magnetic and gravitational interaction. The verification of the 4π-symmetry of spinor wave functions and of the spin superposition law at a macroscopic scale and the observation of gravitational effects including the Sagnac effect have been widely debated in literature. The coupling of the neutron magnetic moment to resonator coils permitted the coherent energy exchange between the neutron quantum system and the macroscopic resonator. This phenomenon provided the basis for the observation of the magnetic Josephson effect with an energy sensitivity of 10-19 eV. Partial beam path detection experiments are in close connection with the development of quantum mechanical measurement theory. The very high sensitivity of neutron interferometry may be used in future for new fundamental-, solid-state and nuclear-physics application. A striking spectral modulation effect has been observed by means of a proper post-selection procedure under conditions where the spatial shift of the wave trains greatly exceeds the coherence length of the neutron beams traversing an interferometer. It is shown that Schroedinger-cat-like states are created by the superposition of two coherent states generated in the interferometer. These entangled states exhibit under certain circumstances characteristic squeezing phenomena indicating a highly non-classical behavior. Analogies with light optical experiments are discussed. (author) 10 figs., 66 refs