Metrology and Many-Body Physics with Ultracold Metastable Helium

TL;DR

This paper discusses how ultracold metastable helium gases serve as precise tools for atomic structure measurements, testing fundamental physics, and exploring many-body quantum phenomena like Bose-Einstein condensation and superfluidity.

Contribution

It introduces new experimental techniques for laser spectroscopy of helium and explores the potential of metastable helium for quantum many-body physics research.

Findings

High-precision measurements of helium resonances and transition rates.

Observation of quantum depletion in Bose-Einstein condensates.

Progress towards optical lattice trapping of helium atoms.

Abstract

Ultracold dilute gases provide ideal settings for measurements of atomic structure. Helium has an internal structure sufficiently simple to permit highly accurate predictions of its resonances and transition rates. Precise laser spectroscopy of helium thus yields empirical constraints on such calculations. These are desirable in the ongoing investigations seeking to reconcile the disagreement between independent determinations of nuclear charge radius data in both hydrogenic and helium atoms. Either the size of these particles are truly constant and quantum electrodynamics (QED) is flawed, or the theory is correct and some new physics is at play at the atomic scale. Ultracold bose gases also serve as ideal testing ground to better understand the physics of Bose-Einstein condensation, superfluidity, and the effects of weak interactions in condensed-matter systems. The large internal energy of helium's metastable excited state enables the measurement of the momentum of single atoms, providing a new lens through which to examine both weakly-interacting and strongly-correlated systems. This feature is employed to investigate the quantum depletion of a BEC after expansion into the far-field. Finally, the appendix reports on early progress towards the realization of an optical lattice trap for helium.