Phys. Rev. Lett. 108, 090402 (2012)

It is well-known that the performance of large or very sensitive interferometers can be affected by the rotation of the Earth. Indeed, this dependence is put to good use by laser ring gyroscopes, which can detect and measure the Earth's rotation through the Sagnac effect. Now, Shau-Yu Lan and colleagues from the University of California, Berkeley, Lawrence Berkeley National Laboratory and the University of Vienna have significantly improved the contrast of their large space–time atom interferometer by compensating for the Coriolis effect associated with the Earth's motion. In their experiment, laser beams are generated from a 6 W Ti:sapphire laser using acousto-optic modulators for frequency tuning. The Doppler effect is used to select a single pair of counter-propagating frequencies that are resonant with atoms launched ballistically from a 1.5-m-tall fountain of caesium atoms. A retroflection mirror mounted flexibly on top of the vacuum chamber is calibrated by a tilt sensor and moved by piezoelectric actuators to compensate for the Earth's rotation. This Coriolis-corrected interferometer could be used to measure gravity at improved accuracies; the authors predict that the uncertainty in gravitational measurements could be reduced from 6 × 10−8g to around 1 × 10−9g.