Gravitational induced phases in neutron interferometry

Gravitational phases induced on the neutron shall systematically be investigated in large neutron interferometers. In the perfect crystal interferometer, a single neutron is macroscopically separated by several centimetres and experiences phase shifts depending on the height of one path above the other. But the hitherto measured phase shifts are approximately 1% lower than expected. As the gravitational phase shift increases with the interferometer size the new generation of large neutron interferometers will be much more sensitive to gravitation. Our aim is the verification of the Newtonian gravitation law for a macroscopically separated very light sub-atomar quantum object. The same setup will be exploited for sensing hypothetic non-Newtonian short-range interactions by accurately measuring the coherent scattering length of silicon in a perfect crystal at different lattice reflections. A special feature of our setup is the sensitivity to the submicron interaction regime.

Within the framework of this project we fabricated the worlds largest crystal interferometer with a length of 30 cm and a beam separation of 6 cm. Single neutrons are able to split and travel coherently along such macroscopic distances. Finally, they re-combine at the interferometers output and show interference. On their path through the interferometer neutrons become very sensitive to the presence of fields, e.g. the postulated chameleon field as a prominent candidate for describing dark energy. For the detection of chameleons we inserted a cuvette in the interfering paths, expecting the chameleon to show up only in vacuum and be largely suppressed under the presence of air in the cuvette. However, despite precise interference measurements and applying different air pressures the chameleon didnt emerge, however, our experiments will be very useful for setting new limits on key field parameters like the interaction strength of chameleons with matter.