Coherent Three-Photon Excitation of the Strontium Clock Transition

We recently demonstrated a steady-state Bose-Einstein condensate of strontium atoms. We could turn this into a perpetual atom laser if an efficient outcoupling mechanism is found. Here we show a coherent three-photon excitation of the clock transition in a strontium BEC with contrast of over 50\%. We follow it up with a demonstration of three-photon STIRAP-like transfer. In the future, we could use this process to coherently outcouple the atoms from a trap operating at tune-out wavelength.