Probing gravity with trapped atoms: the optical lattice atom interferometer*

Atom interferometers are quantum mechanical devices sensitive to gravitational and inertial forces, with applications in fundamental physics and inertial sensing in the field. Their performance is currently limited by the interrogation time available to freely falling atoms in Earth's gravitational field, as well as noise due to mechanical and acoustic vibrations. Our experiment probes gravitational potentials by holding, rather than dropping, atoms. We realize an interrogation time of up to 25 seconds by suspending the spatially separated atomic wave packets in an optical lattice mode-filtered by an optical cavity. This trapped geometry suppresses phase variance due to vibrations by three to four orders of magnitude, overcoming the dominant noise source in atom-interferometric gravimeters. We describe recent progress in characterizing and reducing decoherence of the interferometer. An upgraded optical lattice interferometer experiment is currently being commissioned, with the goal of increased sensitivity to gravity.