Inelastic collision rates of trapped metastable hydrogen

Abstract

We report the first detailed decay studies of trapped metastable $(2S)$ hydrogen. By two-photon excitation of ultracold H samples, we have produced clouds of at least $5\ifmmode\times\else\texttimes\fi{}{10}^{7}$ magnetically trapped $2S$ atoms at densities greater than $4\ifmmode\times\else\texttimes\fi{}{10}^{10}{\mathrm{cm}}^{\ensuremath{-}3}$ and temperatures below $100\ensuremath{\mu}\mathrm{K}.$ At these densities and temperatures, two-body inelastic collisions of metastable atoms are evident. Experimental values for the total two-body loss rate constant are ${K}_{2}{=1.8}_{\ensuremath{-}0.7}^{+1.8}\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}9}{\mathrm{cm}}^{3}{\mathrm{s}}^{\ensuremath{-}1}$ at $87\ensuremath{\mu}\mathrm{K}$ and ${K}_{2}{=1.0}_{\ensuremath{-}0.5}^{+0.9}\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}9}{\mathrm{cm}}^{3}{\mathrm{s}}^{\ensuremath{-}1}$ at $230\ensuremath{\mu}\mathrm{K}.$ These results are in the range of recent theoretical calculations for the total $2S\ensuremath{-}2S$ inelastic rate constant. The metastable clouds were excited in a gas of ground-state $(1S)$ hydrogen with peak densities reaching $7\ifmmode\times\else\texttimes\fi{}{10}^{13}{\mathrm{cm}}^{\ensuremath{-}3}.$ From the one-body component of the metastable decay, we derive experimental upper limits for ${K}_{12},$ the rate constant for loss due to inelastic $1S\ensuremath{-}2S$ collisions.