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SPIE Quantum Information Science, Sensing, and Computation

Demonstration of a field-deployable vector magnetometer using synchronous coherent population trapping and feedback compensation mechanism

Renu Tripathi, G. S. Pati, Mauricio Pulido

Published Jun 7, 2024• 0 citations
Publisher

Abstract

We have developed a field-deployable vector magnetometer using a small rubidium vapor cell, which is capable of measuring the magnitude and direction of the earth's magnetic field with high accuracy and sensitivity. The magnetometer measures Larmor precession of rubidium atoms using the phenomenon, called synchronous coherent population trapping (SCPT). This gives the advantage of producing a high contrast and narrow linewidth resonance needed for measuring the magnetic field with high accuracy and sensitivity. The magnetometer exhibits sub-nT/√Hz sensitivities in measuring the field components along the three directions.

DOI
10.1117/12.3013511

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We have developed a field-deployable vector magnetometer using a small rubidium vapor cell, which is capable of measuring the magnitude and direction of the earth's magnetic field with high accuracy and sensitivity. The magnetometer measures Larmor precession of rubidium atoms using the phenomenon, called synchronous coherent population trapping (SCPT). This gives the advantage of producing a high contrast and narrow linewidth resonance needed for measuring the magnetic field with high accuracy and sensitivity. The magnetometer exhibits sub-nT/√Hz sensitivities in measuring the field components along the three directions.
Vector magnetic field measurement is required in several applications including magnetic surveys, navigation and anomalies detection. We have designed and developed a vector magnetometer prototype that can be deployed in the field to survey earth’s magnetic field. Vector operation is enabled in this prototype by using the phenomenon of synchronous coherent population trapping (SCPT), and combining it with a feedback compensation mechanism. The prototype utilizes a small rubidium cell which is placed inside a three-axis field coil. Magnetic field along each axis is measured by performing a peak-lock on one of the strongest resonances produced by SCPT and compensating the external magnetic field via servo control of the three-axis field coil. Under this locked condition, the feedback current applied to each coil in the three-axis system gives a real-time, single-shot measurement of the magnetic field components. Extensive testing of the prototype is being done by performing magnetic field measurements in the magnetically noisy environment inside the laboratory and in-comparison with that of a fluxgate sensor.
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.
A sensor for magnetic field measurement is developed using a small (centimeter size) rubidium cell. A high contrast Zeeman coherent population trapping (CPT) resonance is produced by the magnetic dither in the sensor solenoid, and a peak-locked servo is implemented for magnetic field measurement. Sensitivity close to 110 pT/ √Hz has been achieved in axial field measurement. The CPT-based magnetic sensor is capable of measuring sub-nanotesla level magnetic field variations at high (microtesla) field strength. We discussed possible sources of noise and broadening which are affecting the performance of the sensor, and suggest changes that will further improve the performance of the sensor.