Towards levitated, macroscopic-scale atom interferometry with strontium for precision gravity gradiometry*

Light-pulse atom interferometry is a versatile and powerful tool for conducting precise measurements of fundamental constants, testing general relativity, searching for signatures of new physics, and investigating quantum mechanics on a macroscopic scale. For atom interferometry, pulses of light are used to create the atom optics equivalents of beam-splitters and mirrors. Recent advances in atomic clocks have illustrated the advantages of using strontium, an alkali-earth atom, over the typically used alkali atoms due to its decreased sensitivity to backgrounds such as magnetic fields. We present progress toward the realization of a two-meter atomic fountain at Northwestern University that will be used to develop atom interferometry with large spacetime areas and long interrogation times by levitating the atoms using optical lattices. Initial interferometry will be performed using sequential Bragg transitions for the atom optics pulses. Large spatial separations are enabled in part by spectral engineering of the atom optics beams to compensate for intensity-dependent phase shifts. The two-meter fountain will be used for precision gravitational measurements such as a measurement of the gravitational constant G and for a precise test of the inverse-square law for gravity.