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Sensors

Chip-Scale Ultra-Low Field Atomic Magnetometer Based on Coherent Population Trapping

Hyun-Gue Hong, Sang Eon Park, Sang-Bum Lee, Myoung-Sun Heo, Jongcheol Park, Tae Hyun Kim, Hee Yeon Kim, Taeg Yong Kwon

Published Feb 22, 2021• 19 citations
Publisher

Abstract

We report a chip-scale atomic magnetometer based on coherent population trapping, which can operate near zero magnetic field. By exploiting the asymmetric population among magnetic sublevels in the hyperfine ground state of cesium, we observe that the resonance signal acquires sensitivity to magnetic field in spite of degeneracy. A dispersive signal for magnetic field discrimination is obtained near-zero-field as well as for finite fields (tens of micro-tesla) in a chip-scale device of 0.94 cm3 volume. This shows that it can be readily used in low magnetic field environments, which have been inaccessible so far in miniaturized atomic magnetometers based on coherent population trapping. The measured noise floor of 300 pT/Hz1/2 at the zero-field condition is comparable to that of the conventional finite-field measurement obtained under the same conditions. This work suggests a way to implement integrated atomic magnetometers with a wide operating range.

DOI
10.3390/s21041517

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We report a chip-scale atomic magnetometer based on coherent population trapping, which can operate near zero magnetic field. By exploiting the asymmetric population among magnetic sublevels in the hyperfine ground state of cesium, we observe that the resonance signal acquires sensitivity to magnetic field in spite of degeneracy. A dispersive signal for magnetic field discrimination is obtained near-zero-field as well as for finite fields (tens of micro-tesla) in a chip-scale device of 0.94 cm3 volume. This shows that it can be readily used in low magnetic field environments, which have been inaccessible so far in miniaturized atomic magnetometers based on coherent population trapping. The measured noise floor of 300 pT/Hz1/2 at the zero-field condition is comparable to that of the conventional finite-field measurement obtained under the same conditions. This work suggests a way to implement integrated atomic magnetometers with a wide operating range.
Atomic magnetometer operating in spin-exchange-relaxation-free (SERF) regime has a wide range of applications due to its ultra-high sensitivity. However, the requirement of operating in near-zero magnetic field restricts some of the applications which need the atomic magnetometer to work in the high field environment such as monitoring the magnetic anomalies. A novel scheme of the chip-scale SERF atomic magnetometer operating in geomagnetic field without magnetic shield is demonstrated here. A 18 bits high-precise digital-to-analog converter (DAC) is applied to ensure the stability of the compensated magnetic field. The fluctuation of the compensated magnetic field is less than 8.3nT and a measurement sensitivity of 12.4pT/Hz1/2 is achieved in the laboratory environment without any magnetic shields.
Using the techniques of microelectromechanical systems, we have constructed a small low-power magnetic sensor based on alkali atoms. We use a coherent population trapping resonance to probe the interaction of the atoms’ magnetic moment with a magnetic field, and we detect changes in the magnetic flux density with a sensitivity of 50pTHz−1∕2 at 10Hz. The magnetic sensor has a size of 12mm3 and dissipates 195mW of power. Further improvements in size, power dissipation, and magnetic field sensitivity are immediately foreseeable, and such a device could provide a hand-held battery-operated magnetometer with an atom shot-noise limited sensitivity of 0.05pTHz−1∕2.
We propose and experimentally investigate a coherent population trapping state based magnetometer prototype with 87 Rb atoms. Through modulating Zeeman sublevels with an ac magnetic field, not only a phase sensitive detection scheme suitable for miniature magnetometer is realized, but also the detection resolution of magnetic field intensity could be improved by a factor of two. Our study result indicates that it is a promising low power consumption miniature sensitive low magnetic field sensor offering spatially resolved measurement at the sub-millimetre level.
An atomic magnetometer based on coherent population trapping (CPT) resonances in microfabricated vapor cells is demonstrated. Fabricated by the micro-electro-mechanical-system (MEMS) technology, the cells are filled with Rb and Ne at a controlled pressure. An experimental apparatus is built for characterizing properties of microfabricated vapor cells via the CPT effects. The typical CPT linewidth is measured to be about 3 kHz (1.46 kHz with approximately zero laser intensity) for the rubidium D1 line at about 90 °C. The effects of pressure, temperature and laser intensity on CPT linewidth are studied experimentally. A closed-loop atomic magnetometer is finally finished with a sensitivity of 210.5 pT/Hz1/2 at 1 Hz bandwidth. This work paves the way for developing an integrated chip-scale atomic magnetometer in the future.
A cesium atomic magnetometer based on laser-pumped rf resonance has been investigated and demonstrated experimentally. Atoms are polarized and pumped to dark states by circularly polarized light. When there exists a magnetic field, the corresponding magnetization will be precessing around the magnetic field at Larmor frequency. By means of adding a resonant rf magnetic field, the atoms will be depolarized and absorb photons again. By detecting the spectrum of the transmitted light, one can obtain the information about the external magnetic field. We build an 894nm external cavity diode laser with a frequency stabilization device, and a low noise magnetic field measurement environment. After the optimization of the magnetometer parameter and closed-loop measurement, an ultimate sensitivity of 19 fT/Hz1/2 and an intrinsic sensitivity of 1.8 pT/Hz1/2 have been achieved with the spatial resolution smaller than 2 cm.
Coherent population trapping(CPT)magnetometer is based on coherent population trapping coherent dark states,using an all-optical method to measure the magnetic field with high accuracy.In our experiment,we used the method of injection locking to get the two color lasers with locked phase and large frequency difference,which equald to the hyperfine splitting of the cesium atoms′ground states,and observed the CPT transmission signals.We added the longitudinal magnetic field which was along the laser propagation direction,and observed the widen CPT transmission peak and the splitting signals.For the magnetic field of medium intensity,we got the magnetic field value by measuring the splitting spacing,and for the weak region,the value could be obtained by the relation of current and magnetic field.In our experiment,we could measure the static field with several nT.