Frequency measurements of transitions from the $2^{3\!}P_2$ state to the $5^{1\!}D_2$, $5^{3\!}S_1$, and $5^{3\!}D$ states in ultracold helium

TL;DR

This study uses laser absorption spectroscopy on ultracold helium to precisely measure energy intervals between specific excited states, including the first observation of a spin-forbidden transition, improving measurement accuracy significantly.

Contribution

It provides highly precise measurements of helium energy levels and reports the first observation of a spin-forbidden transition in helium.

Findings

Improved measurement precision by at least an order of magnitude.

First observation of the $2^{3}P_2 - 5^{1}D_2$ transition.

Experimental results agree with theoretical predictions within uncertainties.

Abstract

We perform laser absorption spectroscopy with ultracold $^4$He atoms to measure the energy intervals between the $2^{3\!} P_2$ level and five levels in the n = 5 manifold. The laser light perturbs the cold atomic cloud during the production of Bose-Einstein condensates and decreases the phase space density, causing a measurable decrease in the number of atoms in the final condensate. We improve on the precision of previous measurements by at least an order of magnitude, and report the first observation of the spin-forbidden $2^{3\!}P_2 - 5^{1\!}D_2$ transition in helium. Theoretical transition energies agree with the observed values within our experimental uncertainty.