Neutron interferometry with split-crystal technology.

Perfect crystal interferometers have been a powerful tool to study the foundations of quantum mechanics for almost half a century. Different geometries and sizes of monolithic neutron interferometers have been used to explore a wide range of interactions of thermal neutrons. The main limitation of these experiments is the size of the monolithic crystals. While split-crystal X-ray interferometers have been in use since the 1970s to measure the Si lattice parameter, state-of-the-art neutron interferometers are still based on monolithic crystals. A promising solution to dramatically improve the sensitivity of neutron interferometers would be an interferometer consisting of separated crystals. We report on the first successful operation of a symmetric split-crystal interferometer performed at the high-flux reactor of the ILL (Grenoble, France), where the Atominstitut (Wien, Austria) owns a permanent thermal-neutron beamline. This proof-of-principle demonstration is just as valid also for more performant skew-symmetric setups and shows that experiments requiring long and variable interferometer arms can be realistically considered.