Challenges
Datasets
Workspaces
Papers
Discussions
Leaderboard
Log inSign up
Challenges
Datasets
Workspaces
Papers
Discussions
Leaderboard
Blog
Job Board
Q3AS

© 2026 Aqora Quantum S.A.S.

TermsPrivacyLegal Notice

Physical Review Applied

Free-induction-decay 4 He magnetometer using a multipass cell

Kaiwen Yi, Yang Liu, Bowen Wang, Wei Xiao, Dong Sheng, Xiang Peng, Hong Mei Guo

Published Jul 31, 2024• 25 citations
Publisher

Abstract

Optically pumped magnetometers (OPMs) based on the free-induction-decay (FID) configuration have recently attracted interest owing to their advantages, such as being calibration-free, easy to operate, and showing reduced light shifts induced by the pump light. Currently, alkali-metal vapor cells have been employed in most of the FID magnetometers. However, the relatively narrow linewidth of the magnetic resonance signal and nonlinear Zeeman (NLZ) effects generate bandwidth limitation and heading errors of these magnetometers in the Earth's field, respectively. In this work, we propose a ${}^{4}\mathrm{He}$-based FID magnetometer, which not only has the advantages of being NLZ-free and showing a high bandwidth, but also maintains an enhanced sensitivity assisted by a multipass cell. This magnetometer demonstrates a magnetic field noise floor of $0.34\phantom{\rule{0.2em}{0ex}}\mathrm{pT}/{\mathrm{Hz}}^{1/2}$ with a Nyquist-limited bandwidth of $5$ kHz, which opens another route for atomic magnetometry using FID signals, and exhibits potential for applications in high-frequency magnetic field detection, such as biomagnetic measurements and magnetic communications in the geomagnetic field.

DOI
10.1103/physrevapplied.22.014084

Related papers

Free Induction Decay Optically Pumped Magnetometers: A Review

Jiarui Liu, Xiao Liu, Yuantian Lu +4 more

Free induction decay (FID) optically pumped magnetometers are among the most sensitive quantum sensors available for high-precision magnetic field measurements. This review summarizes recent advances in FID magnetometers, which represent a critical technological route that suppresses systematic errors by temporally separating atomic polarization from magnetic field detection. This review covers light-modulated optical pumping schemes (such as the Bell-Bloom mode), radio-frequency excitation schemes, and magnetic-field-enhanced pumping schemes. Key technological developments, including chip-scale MEMS fabrication, optical multipass architectures, advanced frequency estimation algorithms, and error suppression methods, are also discussed. Finally, emerging trends toward higher integration, environmental robustness, and intelligent signal demodulation are highlighted. These trends provide insights into the development of next-generation high-performance quantum sensors and their growing role in biomedical and geophysical applications, as well as in fundamental scientific research.

Sensors•Sep 26, 2026•0 citations

Dead-zone-free free-induction-decay alkali-metal atomic magnetometer

X.-K. Wang, J. He, HH Deng +2 more

The detection dead zone is an important systematic limitation in scalar atomic magnetometers, constraining their practical utility. In this work, we demonstrate a sensitive dead zone free scalar magnetometer by integrating previously established techniques into a FID magnetometer based on Bell Bloom optical pumping. The dead zone is eliminated by inserting a reflecting mirror within a multipass cavity assisted atomic cell, which folds the optical beam into orthogonal paths. Our analysis reveals that interregion cross talk is essential for interpreting the resulted experimental signals. The sensor exhibits oscillation signal amplitude variations within a factor of three across all orientations in three dimensional space, and a field sensitivity better than 80 fT/Hz^(1/2) over the full space. We further characterize the heading error in the geomagnetic field range, where experimental results agree with theoretical predictions within 0.7 nT. Additionally, the sensor can operate in a closed loop mode by feeding back the real time frequency extracted from the FID signal to modulate the pump beam, we characterize the magnetic field slew rate of the sensor. This work paves the way towards a sensitive vector FID magnetometer.

arXiv:2609.04847•Physical Review A•Aug 25, 2026•0 citations

A Multi-Pass Optically Pumped Rubidium Atomic Magnetometer with Free Induction Decay

Lulu Zhang, Yongbiao Yang, Ni Zhao +2 more

A free-induction-decay (FID) type optically-pumped rubidium atomic magnetometer driven by a radio-frequency (RF) magnetic field is presented in this paper. Influences of parameters, such as the temperature of rubidium vapor cell, the power of pump beam, and the strength of RF magnetic field and static magnetic field on the amplitude and the full width at half maximum (FWHM) of the FID signal, have been investigated in the time domain and frequency domain. At the same time, the sensitivities of the magnetometer for the single-pass and the triple-pass probe beam cases have been compared by changing the optical path of the interaction between probe beam and atomic ensemble. Compared with the sensitivity of ∼21.2 pT/Hz1/2 in the case of the single-pass probe beam, the amplitude of FID signal in the case of the triple-pass probe beam has been significantly enhanced, and the sensitivity has been improved to ∼13.4 pT/Hz1/2. The research in this paper provids a reference for the subsequent study of influence of different buffer gas pressure on the FWHM and also a foundation for further improving the sensitivity of FID rubidium atomic magnetometer by employing a polarization-squeezed light as probe beam, to achieve a sensitivity beyond the photo-shot-noise level.

arXiv:2301.08437•Sensors•Oct 7, 2022•18 citations

FID Magnetometer Based on Paraffin-Coated Planar Reflective Multipass Cells

Xiangyu Li, Tingxuan Guo, Yang Li +1 more

We demonstrate a paraffin-coated planar reflective multipass vapor cell for compact optical atomic magnetometry. The cell has an internal volume of $12 \times 12 \times 8~\mathrm{mm}^3$ and supports 20 optical passes with a total transmittance exceeding $65\%$, while maintaining a longitudinal spin-relaxation time of $^{87}\mathrm{Rb}$ longer than $1~\mathrm{s}$. The planar geometry provides spatially separated input and output beams, enabling compact optical integration. A single-cell free-induction-decay (FID) magnetometer reaches $10~\mathrm{pT}/\sqrt{\mathrm{Hz}}$ in the geomagnetic-field range, presently limited by current-source noise in the field coils. A two-cell differential configuration achieves a sensitivity of $\sim 28~\mathrm{fT}/\sqrt{\mathrm{Hz}}$ over the $1$--$15~\mathrm{Hz}$ band for bias fields of $0.3$--$0.7~\mathrm{G}$. These results establish that paraffin-coated planar multipass cells offer high optical depth, long coherence times, and an integration-friendly platform for ultrasensitive magnetometry.

physics.opticsCross-listedarXiv:2605.01460•May 5, 2026•0 citations

Waveform reconstruction with a Cs based free-induction-decay magnetometer

Dominic Hunter, Ricardo Jiménez-Martínez, Juan A. Herbsommer +3 more

We demonstrate an optically pumped magnetometer (OPM) operated in a free-induction-decay (FID) configuration that is capable of tracking oscillating magnetic signals in the presence of a 50 μT static field. Excellent waveform reconstruction is demonstrated for low frequency modulations with respect to the Nyquist limited bandwidth. A 100 pT oscillation was successfully reconstructed using signal averaging, and an optimum sensitivity of 3.9 pT/Hz was measured from the spectrum of the residuals relative to the sinusoidal fit. The impact of the pump-probe repetition rate and spin depolarization on the frequency response of the sensor is investigated in detail using miniaturized vapor cell technology, with the (-3 dB) bandwidths residing beyond the Nyquist limit in each case. We also discuss technical limitations associated with the magnetometer when exposed to oscillating fields of sufficiently high amplitude or frequency. This is discussed in the context of potential distortions arising in the reproduced signals, induced by frequency modulation (FM) and aliasing artefacts.

Optics Express•Nov 7, 2018•27 citations

Femtotesla 4 He magnetometer with a multipass cell

Yang Liu, Xiang Peng, Haidong Wang +4 more

In this Letter, we propose a single-beam nonlinear magneto-optical rotation (NMOR) magnetometer with a multipass 4 He gas-discharged cell. In contrast to the single-pass cell, the multipass cell allowed laser beams to pass through the metastable-state atomic ensemble 22 times, which directly increases the optical path length and significantly enhances magneto-optical rotation in the 4 He gas sample. Based on nonlinear Faraday rotation, the 4 He magnetometer with the multipass cell demonstrates a noise floor of 9 fT/Hz 1/2 , which approaches the photon-shot noise floor limit of 6.4 fT/Hz 1/2 . In addition, the wider linewidth in metastable-state atoms realizes an NMOR 4 He magnetometer with a 3 dB bandwidth of 4.3 kHz, in contrast to the ultranarrow linewidth in the antirelaxation-coated cells or spin-exchange relaxation-free regime alkali-metal cells with buffer gas. Since the 4 He cell functions without heating or cryogenic cooling, the femtotesla sensitivity and kilohertz-bandwidth 4 He magnetometer exhibits potential in biomagnetic applications such as magnetocardiography and magnetoencephalography.

Optics Letters•Sep 19, 2022•21 citations
Optically pumped magnetometers (OPMs) based on the free-induction-decay (FID) configuration have recently attracted interest owing to their advantages, such as being calibration-free, easy to operate, and showing reduced light shifts induced by the pump light. Currently, alkali-metal vapor cells have been employed in most of the FID magnetometers. However, the relatively narrow linewidth of the magnetic resonance signal and nonlinear Zeeman (NLZ) effects generate bandwidth limitation and heading errors of these magnetometers in the Earth's field, respectively. In this work, we propose a 4He{}^{4}\mathrm{He}4He-based FID magnetometer, which not only has the advantages of being NLZ-free and showing a high bandwidth, but also maintains an enhanced sensitivity assisted by a multipass cell. This magnetometer demonstrates a magnetic field noise floor of 0.34pT/Hz1/20.34\phantom{\rule{0.2em}{0ex}}\mathrm{pT}/{\mathrm{Hz}}^{1/2}0.34pT/Hz1/2 with a Nyquist-limited bandwidth of 555 kHz, which opens another route for atomic magnetometry using FID signals, and exhibits potential for applications in high-frequency magnetic field detection, such as biomagnetic measurements and magnetic communications in the geomagnetic field.
Free induction decay (FID) optically pumped magnetometers are among the most sensitive quantum sensors available for high-precision magnetic field measurements. This review summarizes recent advances in FID magnetometers, which represent a critical technological route that suppresses systematic errors by temporally separating atomic polarization from magnetic field detection. This review covers light-modulated optical pumping schemes (such as the Bell-Bloom mode), radio-frequency excitation schemes, and magnetic-field-enhanced pumping schemes. Key technological developments, including chip-scale MEMS fabrication, optical multipass architectures, advanced frequency estimation algorithms, and error suppression methods, are also discussed. Finally, emerging trends toward higher integration, environmental robustness, and intelligent signal demodulation are highlighted. These trends provide insights into the development of next-generation high-performance quantum sensors and their growing role in biomedical and geophysical applications, as well as in fundamental scientific research.
The detection dead zone is an important systematic limitation in scalar atomic magnetometers, constraining their practical utility. In this work, we demonstrate a sensitive dead zone free scalar magnetometer by integrating previously established techniques into a FID magnetometer based on Bell Bloom optical pumping. The dead zone is eliminated by inserting a reflecting mirror within a multipass cavity assisted atomic cell, which folds the optical beam into orthogonal paths. Our analysis reveals that interregion cross talk is essential for interpreting the resulted experimental signals. The sensor exhibits oscillation signal amplitude variations within a factor of three across all orientations in three dimensional space, and a field sensitivity better than 80 fT/Hz^(1/2) over the full space. We further characterize the heading error in the geomagnetic field range, where experimental results agree with theoretical predictions within 0.7 nT. Additionally, the sensor can operate in a closed loop mode by feeding back the real time frequency extracted from the FID signal to modulate the pump beam, we characterize the magnetic field slew rate of the sensor. This work paves the way towards a sensitive vector FID magnetometer.
A free-induction-decay (FID) type optically-pumped rubidium atomic magnetometer driven by a radio-frequency (RF) magnetic field is presented in this paper. Influences of parameters, such as the temperature of rubidium vapor cell, the power of pump beam, and the strength of RF magnetic field and static magnetic field on the amplitude and the full width at half maximum (FWHM) of the FID signal, have been investigated in the time domain and frequency domain. At the same time, the sensitivities of the magnetometer for the single-pass and the triple-pass probe beam cases have been compared by changing the optical path of the interaction between probe beam and atomic ensemble. Compared with the sensitivity of ∼21.2 pT/Hz1/2 in the case of the single-pass probe beam, the amplitude of FID signal in the case of the triple-pass probe beam has been significantly enhanced, and the sensitivity has been improved to ∼13.4 pT/Hz1/2. The research in this paper provids a reference for the subsequent study of influence of different buffer gas pressure on the FWHM and also a foundation for further improving the sensitivity of FID rubidium atomic magnetometer by employing a polarization-squeezed light as probe beam, to achieve a sensitivity beyond the photo-shot-noise level.
We demonstrate a paraffin-coated planar reflective multipass vapor cell for compact optical atomic magnetometry. The cell has an internal volume of 12×12×8 mm312 \times 12 \times 8~\mathrm{mm}^312×12×8 mm3 and supports 20 optical passes with a total transmittance exceeding 65%65\%65%, while maintaining a longitudinal spin-relaxation time of 87Rb^{87}\mathrm{Rb}87Rb longer than 1 s1~\mathrm{s}1 s. The planar geometry provides spatially separated input and output beams, enabling compact optical integration. A single-cell free-induction-decay (FID) magnetometer reaches 10 pT/Hz10~\mathrm{pT}/\sqrt{\mathrm{Hz}}10 pT/Hz​ in the geomagnetic-field range, presently limited by current-source noise in the field coils. A two-cell differential configuration achieves a sensitivity of ∼28 fT/Hz\sim 28~\mathrm{fT}/\sqrt{\mathrm{Hz}}∼28 fT/Hz​ over the 111--15 Hz15~\mathrm{Hz}15 Hz band for bias fields of 0.30.30.3--0.7 G0.7~\mathrm{G}0.7 G. These results establish that paraffin-coated planar multipass cells offer high optical depth, long coherence times, and an integration-friendly platform for ultrasensitive magnetometry.
We demonstrate an optically pumped magnetometer (OPM) operated in a free-induction-decay (FID) configuration that is capable of tracking oscillating magnetic signals in the presence of a 50 μT static field. Excellent waveform reconstruction is demonstrated for low frequency modulations with respect to the Nyquist limited bandwidth. A 100 pT oscillation was successfully reconstructed using signal averaging, and an optimum sensitivity of 3.9 pT/Hz was measured from the spectrum of the residuals relative to the sinusoidal fit. The impact of the pump-probe repetition rate and spin depolarization on the frequency response of the sensor is investigated in detail using miniaturized vapor cell technology, with the (-3 dB) bandwidths residing beyond the Nyquist limit in each case. We also discuss technical limitations associated with the magnetometer when exposed to oscillating fields of sufficiently high amplitude or frequency. This is discussed in the context of potential distortions arising in the reproduced signals, induced by frequency modulation (FM) and aliasing artefacts.
In this Letter, we propose a single-beam nonlinear magneto-optical rotation (NMOR) magnetometer with a multipass 4 He gas-discharged cell. In contrast to the single-pass cell, the multipass cell allowed laser beams to pass through the metastable-state atomic ensemble 22 times, which directly increases the optical path length and significantly enhances magneto-optical rotation in the 4 He gas sample. Based on nonlinear Faraday rotation, the 4 He magnetometer with the multipass cell demonstrates a noise floor of 9 fT/Hz 1/2 , which approaches the photon-shot noise floor limit of 6.4 fT/Hz 1/2 . In addition, the wider linewidth in metastable-state atoms realizes an NMOR 4 He magnetometer with a 3 dB bandwidth of 4.3 kHz, in contrast to the ultranarrow linewidth in the antirelaxation-coated cells or spin-exchange relaxation-free regime alkali-metal cells with buffer gas. Since the 4 He cell functions without heating or cryogenic cooling, the femtotesla sensitivity and kilohertz-bandwidth 4 He magnetometer exhibits potential in biomagnetic applications such as magnetocardiography and magnetoencephalography.