Lattice atom interferometer in an optical cavity

In quantum metrology and quantum information processing, a coherent nonclassical state must be manipulated before unwanted interactions with the environment lead to decoherence. In atom interferometry, the nonclassical state is a spatial superposition, where each atom coexists in multiple locations at once as a collection of phase-coherent partial wavepackets. These states enable precise measurements in fundamental physics and inertial sensing. However, atom interferometers usually use atomic fountains, where the available free-fall time sets a hard time limit on the interrogation of the quantum state. We instead realize atom interferometry with a coherent spatial superposition state held by an optical lattice for longer than 1 minute, which is more than 25 times longer than any atomic fountain interferometer. This performance was made possible by recent advances in the understanding and control of coherence-limiting mechanisms. An order of magnitude increase in sensitivity enables near-term applications such as gravimetry measurements, searches for fifth forces, or fundamental probes into the non-classical nature of gravity.