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Current Optics and Photonics

Optimization of a Radio-frequency Atomic Magnetometer Toward Very Low Frequency Signal Reception

Hyun Joon Lee, Ye-Jin Yu, Jang‐Yeol Kim, J. Lee, Han Seb Moon, In‐Kui Cho

Published Jun 25, 2021• 1 citation
Publisher

Abstract

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.

DOI
10.3807/copp.2021.5.3.213

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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.

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Abstract An atomic magnetometer (AM) is very sensitive to magnetic fields and useful in many applications. AM works by optical interrogation of orientation of alkali-atom spins in a vapor cell. Since the sensitivity characterizes the performance of AM, it should be optimized. We investigate the effect of the gain of a balanced photodetector on the sensitivity of an RF atomic magnetometer setup. While the amplitude of RF signal (BRF) varies between 0.1-10 nT, the frequency is fixed at 100 kHz. The gain of the balanced photodetector varies between 103 - 107 V/A. the noise density and AM signal are measured to calculate the signal-to-noise ratios (SNR) and the AM sensitivity. The results show that noise density increases with the gain value. The AM signal increases with both BRF as well as the gain value. SNR increases with BRF while the AM sensitivity is independent on BRF. When the gain is increased from 103 - 105 V/A, SNR increases and reaches a maximum while the AM sensitivity decreases and reaches a minimum value of 0.4 pT/√Hz. However, SNR and the AM sensitivity are almost unchanged for the gain value of 105 - 107 V/A. Therefore, the gain of balanced photodetector in our AM setup should be set sufficiently high, at least 105 V/A.

Journal of Physics Conference Series•Jun 1, 2025•0 citations
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.
Radio communication through attenuating media necessitates the use of very-low frequency (VLF) and ultra-low frequency (ULF) carrier bands, which are frequently used in underwater and under-ground communication applications. Quantum sensing techniques can be used to circumvent hard constraints on the size, weight and noise floor of classical signal transducers. In this low-frequency range, an optically pumped atomic sample can be used to detect carrier wave modulation resonant with ground-state Zeeman splitting of alkali atoms. Using a compact, self-calibrating system we demonstrate a resonant atomic transducer for digital data encoded using binary phase- and frequency-keying of resonant carrier waves in the 200 Hz -200 kHz range. We present field trial data showing sensor noise floor, decoded data and received bit error rate, and calculate the projected range of sub-sea communication using this device.
We describe an alkali-metal magnetometer for detection of weak magnetic fields in the radio-frequency (rf) range. High sensitivity is achieved by tuning the Zeeman resonance of alkali atoms to the rf frequency and partially suppressing spin-exchange collisions in the alkali-metal vapor. We demonstrate magnetic field sensitivity of 2 fT/Hz(1/2) at a frequency of 99 kHz with a resonance width of 400 Hz. We also derive a simple analytic expression for the fundamental limit on the sensitivity of the rf magnetometer and show that a sensitivity of about 0.01 fT/Hz(1/2) can be achieved in a practical system with a measurement volume of 200 cm3.
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.
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.
Abstract An atomic magnetometer (AM) is very sensitive to magnetic fields and useful in many applications. AM works by optical interrogation of orientation of alkali-atom spins in a vapor cell. Since the sensitivity characterizes the performance of AM, it should be optimized. We investigate the effect of the gain of a balanced photodetector on the sensitivity of an RF atomic magnetometer setup. While the amplitude of RF signal (BRF) varies between 0.1-10 nT, the frequency is fixed at 100 kHz. The gain of the balanced photodetector varies between 103 - 107 V/A. the noise density and AM signal are measured to calculate the signal-to-noise ratios (SNR) and the AM sensitivity. The results show that noise density increases with the gain value. The AM signal increases with both BRF as well as the gain value. SNR increases with BRF while the AM sensitivity is independent on BRF. When the gain is increased from 103 - 105 V/A, SNR increases and reaches a maximum while the AM sensitivity decreases and reaches a minimum value of 0.4 pT/√Hz. However, SNR and the AM sensitivity are almost unchanged for the gain value of 105 - 107 V/A. Therefore, the gain of balanced photodetector in our AM setup should be set sufficiently high, at least 105 V/A.