Cold collision frequency shift of the 1S-2S transition in hydrogen

Abstract

We have observed the cold collision frequency shift of the 1S-2S transition in trapped spin-polarized atomic hydrogen. We find Δν1S-2S = −3.8 ± 0.8 × 10−10n Hz cm3, where n is the sample density. From this we derive the 1S-2S s-wave triplet scattering length, a1S-2S = −1.4 ± 0.3 nm, which is in fair agreement with a recent calculation. The shift provides a valuable probe of the distribution of densities in a trapped sample. © 1998 American Physical Society.