Location-dependent Raman transition in gravity-gradient measurements using dual atom interferometers

Abstract

The location-dependent Raman transition was investigated based on dual atom interferometers which were designed for gravity-gradient measurements. The cross talk between the Raman beam pairs generated by an electro-optical modulator make the Raman transition location dependent. Therefore, the fringe contrast also depends on the location where the Raman pulses interact with the atoms, so it is important to adjust the interaction location to optimize the precision of the gravity-gradient measurements. To further reduce the residual cross talk, the detuning of the Raman beams for $^{85}\mathrm{Rb}$ atoms was controlled using the saturated absorption spectra of the $^{87}\mathrm{Rb}$ atoms. The optimal location for the Raman transition was determined by theoretical analysis and modulation experiments, and the atomic trajectory was optimized and applied to the gravity-gradient measurements. The resolution of the differential gravity measurement evaluated by the Allan deviation was $4.9\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}9}$ m/${\mathrm{s}}^{2}$ @ 15 000 s, and the corresponding resolution of the gravity gradient measurement was 7.4 E @ 15 000 s.