Reciprocity theorem and time reversal symmetry in quantum reflection of helium atom beams from a blazed grating

Abstract

In optics, the reciprocity theorem refers the equivalence of the signal detected when the position of detector and beam source are interchanged. The reciprocity theorem has been regarded to be valid not only in classical optics but also in atom and molecule optics. Since it was confirmed in diffraction theory, the reciprocity theorem has been used to understand diffraction efficiencies in various experiments. In atom optics, the reciprocity theorem has been studied in the reflection of an atom from a crystal surface, especially from the repulsive part of the atom-surface interaction potential. We demonstrate reciprocity theorem for quantum reflection of helium atom beam from a blazed grating. Helium atom beams are reflected from a blazed grating at grazing incidence angle. When diffraction efficiencies are plotted against deflection angle, the nth-diffraction-order efficiency for the standard configuration is the same as the –nth-diffraction-order efficiency for the reverse configuration, which confirms the reciprocity theorem. Since the flux is conserved when quantum reflection happens, as well as the reciprocity theorem, the time-reversal invariance holds in our system.