Circulating pulse cavity enhancement as a method for extreme momentum transfer atom interferometry

Large-scale atom interferometers promise unrivaled strain sensitivity to mid-band gravitational waves, and will probe a new parameter space in the search for ultra-light scalar dark matter. These proposals require gradiometry with kilometer-scale baselines, a momentum separation above 10 4 ℏ k between interferometer arms, and optical transitions to long-lived clock states to reach the target sensitivities. Prohibitively high optical power and wavefront flatness requirements have thus far limited the maximum achievable momentum splitting. Here we propose a scheme for optical cavity enhanced atom interferometry, using circulating, spatially resolved pulses, and intracavity frequency modulation to meet these requirements. We present parameters for the realization of 20 kW circulating pulses in a 1 km interferometer enabling 10 4 ℏ k splitting on the 698 nm clock transition in 87 Sr. This scheme addresses the presently insurmountable laser power requirements and is feasible in the context of a kilometer-scale atom interferometer facility.