  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.
