Testing gravity with cold-atom interferometers

We present a horizontal gravity gradiometer atom interferometer for precision gravitational tests. The horizontal configuration is superior for maximizing the inertial signal in the atom interferometer from a nearby proof mass. In our device, we have suppressed spurious noise associated with the horizonal configuration to achieve a differential acceleration sensitivity of 4. 210^-9g/Hz over a 70 cm baseline or 3. 010^-9g/Hz inferred per accelerometer. Using the performance of this instrument, we characterize the results of possible future gravitational tests. We complete a proof-of-concept measurement of the gravitational constant with a precision of 310^-4 that is competitive with the present limit of 1. 210^-4 using other techniques. From this measurement, we provide a statistical constraint on a Yukawa-type fifth force at 810^-3 near the poorly known length scale of 10 cm. Limits approaching 10^-5 appear feasible. We discuss improvements that can enable uncertainties falling well below 10^-5 for both experiments.