Demonstration of improved sensitivity of echo atom interferometers to gravitational acceleration

We have developed two configurations of an echo interferometer that rely on standing wave excitation of a laser-cooled sample of rubidium atoms. Both configurations are sensitive to acceleration along the axis of excitation. For a two-pulse configuration, the signal from the interferometer is modulated at the recoil frequency and exhibits a sinusoidal frequency chirp as a function of pulse spacing. In comparison, for a three-pulse stimulated echo configuration, the signal is observed without recoil modulation and exhibits a modulation at a single frequency as a function of pulse spacing. The three-pulse configuration is less sensitive to effects of vibrations and magnetic field curvature, leading to a longer experimental timescale. For both configurations of the interferometer, we show that a measurement of acceleration with a statistical precision of 0.5% can be realized by analyzing the shape of the echo envelope, which has a temporal duration of a few microseconds. Using the two-pulse interferometer, we obtain measurements of acceleration that are statistically precise to 6 parts per million on a 25 ms timescale. In comparison, using the three-pulse interferometer, we obtain measurements of acceleration that are statistically precise to 75 parts per billion on a timescale of 70 ms. The inhomogeneous field of a magnetized vacuum chamber limited the experimental timescale and resulted in prominent systematic effects. Extended timescales and improved signal-to-noise ratio observed in recent echo experiments using a non-magnetic vacuum chamber suggest that echo techniques are suitable for a high precision measurement of gravitational acceleration g. We discuss methods for reducing systematic effects and improving the signal-to-noise ratio. Simulations suggest that an optimized experiment with improved vibration isolation that utilizes atoms selected in the magnetic sublevel mF = 0 state can result in measurements of g precise to 0.5 parts per billion with a timescale of 300 ms.