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Unshielded Vector Magnetometer Prototype using Synchronous Coherent Population Trapping and Feedback Control

G. S. Pati, Renu Tripathi, Mauricio Pulido

Published Jan 1, 2026• 0 citations
Publisher

Abstract

We discuss a vector magnetometer prototype which operates in unshielded manner to measure earth’s field. It is designed using feedback control of a magnetic resonance produced by synchronous coherent population trapping in a rubidium cell.
DOI
10.1364/cleo_at.2026.am4c.6

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We demonstrate a real-time, single-shot vector magnetic measurement technique using synchronous coherent population trapping (SCPT) in an apparatus consisting of a small rubidium vapor cell. Vector modality of our magnetometer is enabled by designing a feedback system based on performing a peak-lock on a particularly strong 2ΩL magnetic resonance produced in the SCPT spectrum and compensating the external magnetic field via a three-axis field coil. With its current design, this magnetometer exhibits high sensitivities of approximately 155, 129, and 57pT/Hz in measuring the magnetic field vector components along the (x,y,z) axes. Sensitivities closer to the shot-noise limit can be achieved in the future by reducing the technical noise of our equipment and by employing a differential detection and polarization rotation measurement scheme in our system.
We demonstrate a new mechanism, suitable for performing remote earth field measurement using synchronous modulation of two laser fields, which are two-photon resonant with the sodium atom’s hyperfine ground states. This mechanism relies on coherent population trapping (CPT), and thus, called the synchronous CPT scheme. We have measured the magnetic resonances in fluorescence from a sodium cell to demonstrate suitability of this scheme for remote magnetometry. A strong magnetic resonance with its dip corresponding to the Larmor frequency is produced in the presence of a transverse magnetic field. To estimate the optimal duty cycle of light modulation for attaining high performance, we measured the amplitudes and linewidths of the magnetic resonance as a function of the duty cycle, by keeping the peak intensity in CPT fields constant.