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Description
A low energy particle confined by a horizontal reflective surface and gravity settles in gravitationally bound quantum states. These gravitational quantum states (GQS) were so far only observed with neutrons. However, the existence of GQS is predicted also for atoms.
The GRASIAN collaboration pursues the first observation of GQS of atoms, using a cryogenic hydrogen (H) beam. This endeavor is motivated by the higher densities, which can be expected from H compared to neutrons, the easier access, the fact, that GQS were never observed with atoms and the accessibility to hypothetical shortrange interactions. In addition to enabling gravitational quantum spectroscopy, such a cryogenic hydrogen beam with very low vertical velocity components - a few cm/s, can be used for precision optical and microwave spectroscopy.
A major difference between atoms and neutrons is their interaction with surfaces. While neutrons are reflected from the averaged neutron optical potential of the individual nuclei of the surface, atoms undergo quantum reflection (QR) from the attractive Casimir-Polder (CP) potential. This phenomenon only occurs at very low particle energies. In fact, incident velocities in the order of ∼ 10 cm/s are required. Experimentally, QR has been observed for H atoms reflected from liquid helium surfaces, as well as for heavier atoms reflected from various solid surfaces. QR of atomic H from a solid surface has not been demonstrated before.
We report on our recent measurement results on the first observation of quantum reflection of atomic hydrogen from a silicon mirror surface.