Research on the effects of inconsistent initial velocity of the atom clouds in atom gravity gradiometers

The initial state of atom clouds significantly influences the performance of cold-atom inertial sensors, particularly for atom gravity gradiometers (AGGs), where the consistency of the initial state of two atom clouds greatly affects measurement performance. By analyzing the mechanism of polarization gradient cooling (PGC), we investigate its effect on the initial velocity consistency of atomic clouds. In the course of this study, we compare different PGC models and identify a model that has the least influence on initial velocity consistency. Based on this model, the velocity difference between the two atom clouds is modulated by various experimental parameters, such as the laser power attenuation time, which ranges from 1 to 6 s with the laser detuning of -88 MHz. The results indicate that the gravity gradient increases by approximately 66.13 E (1 E = 10^-9 s^-2) for each millimeter per second increase in the velocity difference between the two atomic clouds. The study finds that this velocity difference introduces gravity gradient measurement errors through the two-photon light shift effect. This observation is in excellent agreement with our theoretical calculations. Our study elucidates the mechanism by which the initial velocity difference of atom clouds calibrates instrument measurement errors in AGGs and provides a reference for further enhancing the measurement accuracy of such sensors.