Hydrogen/Deuterium 1S-3S spectroscopy and beyond

In this talk, I would like to present our latest result on the 1S-3S two-photon continuous wave spectroscopy of Deuterium atoms. Studying hydrogen-like atoms is truly exciting, since it can help address some intriguing questions in physics, such as "what is the size of the proton ?!". I will first describe our experiment and the current analysis, then move to our ideas to overcome some of our issue in the future. In the perspective of opening up the field of hydrogen studies, I would like to conclude my talk by introducing our new project: the observation of the gravitational quantum states (GQS) of hydrogen, within the international collaboration GRASIAN (https://grasian.eu). The GQS are formed when a mass-particle is trapped in a potential well formed on one side by the Earth gravitational potential (top confinement) and on the other side, by an atomic mirror (a flat surface placed on the bottom) that reflects the particles upwards. The mechanism behind these specular reflections of the atoms on the mirror is the well-known quantum reflection phenomenon: a very cold mass particle can be seen as a wave-packet that has a high probability of being quantum reflected as it approaches the surface and experiences a rapid and steep change in the potential close to the mirror. These GQS have been observed on ultracold neutrons more than 20 years ago [1], but never with atoms. Our first goal is to observe such gravitational quantum states on hydrogen, which would open the way to new great studies on ultracold hydrogen atoms.

[1] Nesvizhevsky, V., Börner, H., Petukhov, A. et al. Quantum states of neutrons in the Earth's Gravitational field. Nature 415, 297–299 (2002). https://doi.org/10.1038/415297a