Magneto-Optical Trapping and Cooling of Strontium Atoms down to the Photon Recoil Temperature

Abstract

We report narrow-line laser cooling and trapping of strontium atoms down to the photon recoil temperature. ${}^{88}\mathrm{Sr}$ atoms precooled by the broad ${}_{}{}^1{}_{}{}^{}S_0^{}{}_{}{}^{}-{}_{}{}^1{}_{}{}^{}P_1^{}{}_{}{}^{}$ transition at 461 nm were further cooled in a magneto-optical trap using the spin-forbidden transition ${}_{}{}^1{}_{}{}^{}S_0^{}{}_{}{}^{}-{}_{}{}^3{}_{}{}^{}P_1^{}{}_{}{}^{}$ at 689 nm. We have thus obtained an atomic sample with a density over ${10}^{12}\mathrm{cm}{}^{-3\mathrm{}}$ and a minimum temperature of 400 nK, corresponding to a maximum phase space density of ${10}^{-2\mathrm{}}$ which is 3 orders of magnitude larger than the value that has been obtained by magneto-optical traps to date. This scheme provides us an opportunity and system to study quantum statistical properties of degenerate fermions as well as bosons.