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Optics Express

Dual-frequency operation in a single atomic magnetometer and frequency-shift keying modulation of magnetic field communication

Ye-Jin Yu, Han Seb Moon

Published Jun 17, 2025• 3 citations
Publisher

Abstract

We present a dual-frequency operation technique for a radio-frequency atomic magnetometer utilizing a single natural-abundance rubidium (Rb) vapor cell for the first time, and demonstrate a proof-of-concept for magnetic field communication using binary frequency-shift keying (BFSK) under unshielded conditions. The two operational frequencies correspond to the Larmor frequencies of 85 Rb and 87 Rb, as determined by their distinct gyromagnetic ratios in the same magnetic field environment. A rate of 400 symbols/s is adeptly demonstrated with an ambient noise floor of < 20 pT/√Hz, attaining a signal-to-noise ratio of 20 dB. These findings highlight the efficacy of dual-frequency atomic magnetometry as a sophisticated and resilient technique for magnetic field communication in unshielded environments.

DOI
10.1364/oe.566515

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We present a dual-frequency operation technique for a radio-frequency atomic magnetometer utilizing a single natural-abundance rubidium (Rb) vapor cell for the first time, and demonstrate a proof-of-concept for magnetic field communication using binary frequency-shift keying (BFSK) under unshielded conditions. The two operational frequencies correspond to the Larmor frequencies of 85 Rb and 87 Rb, as determined by their distinct gyromagnetic ratios in the same magnetic field environment. A rate of 400 symbols/s is adeptly demonstrated with an ambient noise floor of < 20 pT/√Hz, attaining a signal-to-noise ratio of 20 dB. These findings highlight the efficacy of dual-frequency atomic magnetometry as a sophisticated and resilient technique for magnetic field communication in unshielded environments.
High sensitivity operation of radio-frequency atomic magnetometers in unshielded environment requires compensation of low-frequency fluctuations of the ambient magnetic field. Here we demonstrate the use of phase-lock techniques to stabilise the magnetic environment and achieve high sensitivity at high frequencies. This is achieved by using the output of the atomic magnetometer both for stabilisation and for measurement purposes. The approach is validated by a proof-of-concept in unshielded environment. The phase-lock approach is also compared to the standard approach where the magnetic environment is stabilised with the help of a set of fluxgate magnetometers, and it is shown that the phase-lock approach features superior performances in signal detection.
We describe a single-channel rubidium (Rb) radio-frequency atomic magnetometer (RFAM) as a receiver that takes magnetic signal resonating with Zeeman splitting of the ground state of Rb. We optimize the performance of the RFAM by recording the response signal and signal-to-noise ratio (SNR) in various parameters and obtain a noise level of 159 fT/Hz around 30 kHz. When a resonant radio-frequency magnetic field with a peak amplitude of 8.0 nT is applied, the bandwidth and signal-to-noise ratio are about 650 Hz and 88 dB, respectively. It is a good agreement that RFAM using alkali atoms is suitable for receiving signals in the very low frequency (VLF) carrier band, ranging from 3 kHz to 30 kHz. This study shows the new capabilities of the RFAM in communications applications based on magnetic signals with the VLF carrier band. Such communication can be expected to expand the communication space by overcoming obstacles through the high magnetic sensitive RFAM.
We propose and demonstrate a radio-frequency (rf) atomic magnetometer based on parametric resonances. Previously, most rf atomic magnetometers are based on magnetic resonances and their sensitivities are often limited by spin-exchange relaxation. Here, we introduce a novel scheme for an rf magnetometer where the rf magnetic field is measured by exciting the parametric resonances instead of magnetic resonances using parametric modulation fields. In this way, the spin-exchange relaxation is almost eliminated. Benefiting from the low spin relaxation rate, the parametric resonance scheme exhibits a narrower linewidth and stronger signal, which results in a higher sensitivity. With a 6×6×3 mm^{3} Rb atomic vapor cell, we developed an rf atomic magnetometer with a noise floor of 2 fT/Hz^{1/2}, which is about one order of magnitude higher than the sensitivity achieved in the magnetic-resonance-based scheme. The presented rf detection scheme holds promise in advancing rf atomic magnetometers and brings new insight into their various applications.
We report on a single-channel rubidium radio-frequency atomic magnetometer operating in unshielded environments and near room temperature with a measured sensitivity of 130 fT/Hz. We demonstrate consistent, narrow-bandwidth operation across the kHz–MHz band, corresponding to three orders of magnitude of the magnetic field amplitude. A compensation coil system controlled by a feedback loop actively and automatically stabilizes the magnetic field around the sensor. We measure a reduction in the 50 Hz noise contribution by an order of magnitude. The small effective sensor volume, 57 mm3, increases the spatial resolution of the measurements. Low temperature operation, without any magnetic shielding, coupled with the broad tunability, and low beam power, dramatically extends the range of potential field applications for our device.
We report on a single-channel rubidium radio-frequency atomic magnetometer operating in unshielded \nenvironments and near room temperature with a measured sensitivity of 130 fT/√ \nHz. We demonstrate \nconsistent, narrow-bandwidth operation across the kHz–MHz band, corresponding to three orders \nof magnitude of the magnetic field amplitude. A compensation coil system controlled by a feedback \nloop actively and automatically stabilizes the magnetic field around the sensor. We measure \na reduction in the 50 Hz noise contribution by an order of magnitude. The small effective sensor \nvolume, 57 mm3 \n, increases the spatial resolution of the measurements. Low temperature operation, \nwithout any magnetic shielding, coupled with the broad tunability, and low beam power, dramatically \nextends the range of potential field applications for our device.
Atomic magnetometry was performed at Earth’s magnetic field over a free-space distance of ten meters. Two laser beams aimed at a distant alkali-vapor cell excited and detected the 87Rb magnetic resonance, allowing the magnetic field within the cell to be interrogated remotely. Operated as a driven oscillator, the magnetometer measured the geomagnetic field with ≲3.5 pT precision in a ∼2 s data acquisition; this precision was likely limited by ambient field fluctuations. The sensor was also operated in self-oscillating mode with a 5.3 pT/Hz noise floor. Further optimization will yield a high-bandwidth, fully remote magnetometer with sub-pT sensitivity.