Dark state coupling magnetic field measurement technique for CPT magnetometer

Coherent population trapping (CPT) magnetometer calculates the magnetic field strength by precisely tracking the transmitted signal obtained by the interaction of light and atoms. A dark state coupling measurement scheme is proposed for the system's measurement blind area caused by the directional attenuation of the transmitted signal. The simultaneous excitation and the coupling measurements of multiple dark states are achieved by using modulated light fields with specific frequency. Based on the atomic density matrix method, an atomic five-level system model is established, and the numerical simulation is performed. The control conditions and characteristics of the scheme are analyzed. The experimental results show that the amplitude of transmitted signal obtained by dark coupling measurement can reach about two times of the amplitude of single dark state measurement under the same condition. This scheme can effectively eliminate the measurement blind area, improve the signal-to-noise ratio of the transmitted signal, and further improve the measurement sensitivity of the CPT magnetometer.