Neutron interferometric tests of quantum mechanics

Interferometers based on wavefront and amplitude division have been developed in the past. Most experiments have been performed with the perfect crystal neutron interferometer which provides widely separated coherent beams enabling new experiments in the field of fundamental nuclear- and solid state physics. A nondispersive sample arrangement and the difference between stochastic and deterministic absorption has been investigated. The verification of the 4π-symmetry of spinors and of the quantum mechanical spin-superposition experiment on a macroscopic scale are typical examples of interferometry in spin space. These experiments were continued with two resonance coils in the beams where the results showed that coherence persists, even if an energy exchange between the neutron and the resonator system occurs with certainty. A quantum beat effect was observed when slightly different resonance frequencies were applied to both beams. In this case, an extremely high energy sensitivity of 2.7 x 10-19 eV was achieved. Phase echo systems, experiments with chopped beams and multiplate interferometry are discussed as examples for forthcoming experiments. All the results obtained up until now are in agreement with the formalism of quantum mechanics and stimulate the discussion about the interpretation of this basic theory. (orig.)