GRASIAN: towards the first demonstration of gravitational quantum states of atoms with a cryogenic hydrogen beam.

At very low energies, a light neutral particle above a horizontal surface can experience quantum reflection. The quantum reflection holds the particle against gravity and leads to gravitational quantum states (gqs). So far, gqs were only observed with neutrons as pioneered by Nesvizhevsky and his collaborators at ill. However, the existence of gqs is predicted also for atoms. The Grasian collaboration pursues the first observation and studies of gqs of atomic hydrogen. We propose to use atoms in order to exploit the fact that orders of magnitude larger fluxes compared to those of neutrons are available. Moreover, recently the q-Bounce collaboration, performing gqs spectroscopy with neutrons, reported a discrepancy between theoretical calculations and experiment which deserves further investigations. For this purpose, we set up a cryogenic hydrogen beam at 6  K . We report on our preliminary results, characterizing the hydrogen beam with pulsed laser ionization diagnostics at 243  nm .

Stable high power deep-uv enhancement cavity in ultra-high vacuum with fluoride coatings.

We demonstrate the superior performance of dielectric fluoride coatings versus oxide coatings in long term vacuum operation of a high power deep-ultraviolet enhancement cavity. In ultra-high vacuum (10-8 mbar), the fluoride optics can maintain up to 10 W of stable intracavity power on one hour time scales, a record-high at these vacuum levels, whereas for the oxide optics, we observe rapid degradation at lower intracavity powers with a rate that increases with power. After observing degradation in high vacuum, we can recover the fluoride and oxide optics with oxygen; however, this recovery process becomes ineffective after several applications. For the fluoride optics, we see that initial UV conditioning in an oxygen environment helps to improve the performances of the optics. In oxygen-rich environments from ∼10-4 mbar, the fluoride optics can stably maintain up to 20 W of intracavity power on several-hour time scales whereas for the oxide optics there is immediate degradation with a rate that increases with decreasing oxygen pressure.