Light shift suppression for a vector CPT magnetometer

Vector magnetometers based on coherent population trapping (CPT) measures both orientations and magnitudes of the magnetic fields. Its potential of low SWAPs makes it attractive for applications like magnetic navigation, space and earth geophysics, and magnetic anomaly detection where the stability and accuracy are critical. In this work, we demonstrate a scheme to suppress the light shift by using linearly polarized light and a differential measurement between magnetic resonances to improve the long-term stability.

The radio frequency that creates the optical sidebands for CPT quickly switches between two magnetic sensitive transitions with direct digital synthesizer (DDS), and the magnetic field is extrapolated from the difference of the center frequencies of the magnetic resonances. Vector light shift vanishes when using a linear polarization for CPT. Scalar and tensor light shifts as well as other common drifts like temperature-dependent collisional shifts from buffer gas are suppressed through careful choice of measured resonances.  We show the light shift reduction by more than a factor of 20 with the proposed scheme compared to the CPT magnetometer with circular polarization and the magnetic field measurements using circular and linear polarization agree within 2 nT with an applied filed of 680 μT.