Testing the worldʹs largest monolithic perfect crystal neutron interferometer

Silicon perfect crystal neutron interferometers have some remarkable advantages compared to other matter wave interferometers, e.g. large beam separation, a lot of sample space and easy sample handling without the need of vacuum. In this paper we present a 45° 6-plate interferometer which considerably enlarges the utilizable interferometer space. The path length of the coherent beams reaches 21 cm, the beam separation 5 cm and the enclosed beam area 80 cm2. The 6-plate design allows a verification of how the path length influences the beam coherence and it opens new applications, e.g. measurement of the neutron–electron scattering length or Which-Way experiments. In a first series of visibility measurements, using a scanning slit and a CCD camera, 65% visibility was achieved with an 8×8 mm2 slit and 69% visibility with 4×4 mm2. The large interferometer and the two smaller interferometer loops show the same visibilities, therefore the increased path lengths does not reduce beam coherence. Finally we demonstrate in a combined action of two non-absorbing phase shifters how Which-Way information and visibility can be modulated in the 6-plate interferometer.