Real-world applications of atomic magnetometers require the ability to operate them with high-sensitivity in the presence of magnetic noise. In the present work, high-sensitivity operation of unshielded atomic magnetometers in a magnetically noisy environment is demonstrated. The distinguishing feature of the demonstrated approach is the implementation of active in-situ bias field stabilization using multiple fluxgate magnetometers. This is combined with the use of a counter-propagating pump and triple-pass probe configuration, to maximize the atomic polarization and the probe rotation respectively, so to reach high-sensitivity. The improvement in sensitivity of the unshielded system with respect to previous realizations is fully characterized, with the contributions of the different modifications of the apparatus individually quantified. The presented set-up is suitable for the detection of long-range magnetic fields, where shielding or differential measurements using multi-sensor set-ups do not constitute viable options.
Real-world applications of atomic magnetometers require the ability to operate them with high-sensitivity in the presence of magnetic noise. In the present work, high-sensitivity operation of unshielded atomic magnetometers in a magnetically noisy environment is demonstrated. The distinguishing feature of the demonstrated approach is the implementation of active in-situ bias field stabilization using multiple fluxgate magnetometers. This is combined with the use of a counter-propagating pump and triple-pass probe configuration, to maximize the atomic polarization and the probe rotation respectively, so to reach high-sensitivity. The improvement in sensitivity of the unshielded system with respect to previous realizations is fully characterized, with the contributions of the different modifications of the apparatus individually quantified. The presented set-up is suitable for the detection of long-range magnetic fields, where shielding or differential measurements using multi-sensor set-ups do not constitute viable options.
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 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.
Optically pumped atomic magnetometers are capable of measuring radio-frequency magnetic fields with high sensitivity, but their narrow bandwidth, of the order of 1 kHz, restricts their applications. Further, their full potential is often not realized, with noisy environments or quantum noise curtailing their sensitivity. This study presents a two-chamber atomic magnetometer, with independent control over the tuning field and pumping helicity in each chamber, which addresses both bandwidth and sensitivity limitations. It demonstrates a practical instance of bandwidth expansion, by simultaneous measurement of signals spaced more than 100 kHz apart, at frequencies corresponding to nuclear quadrupole resonance of ammonium nitrate and potassium chlorate, two materials commonly found in improvised explosive devices. It further demonstrates: the intrinsic reduction of common-mode noise, including environmental and probe light-shift noise, down to 2.4 fT/Hz, with the use of resonant, but oppositely pumped, atomic chambers; the reduction of photon shot noise down to 28 aT/Hz with the use of 44 probe passes through the two chambers; and the reduction of atom noise down to 34 aT/Hz, in agreement with prediction, using a large combined volume, 128 cm3, of 87Rb atoms. This work underlines the potential sensitivity of these quantum sensors, while exploring the technical limitation, namely the high pump power required, that stands as a barrier to that sensitivity. Further, it marks a significant step towards utilizing atomic magnetometers in applications demanding broader bandwidth or multiplexing, notably simultaneous measurements at far-spaced radio frequencies.
Miniaturized high-sensitivity atomic magnetometers play a crucial role in biomagnetic measurements. The utilization of multipass cells enhances the sensitivity of atomic magnetometers. This study explores the benefits of employing a multipass cell in spin-exchange relaxation-free (SERF) atomic magnetometers through theoretical and experimental analysis. A signal-to-noise ratio (SNR) model was established by accounting for the optimal detuning frequency of the probe light and low-frequency 1/f noise. This enabled the optimal number of probe light passes through the vapor cell to be determined. Additionally, compact and symmetric reflective optical paths were designed to mitigate polarization gradients in atomic magnetometers with high atomic number density. Experimental results confirmed that the magnetic field sensitivity of the triple-pass configuration (1.8 fT/Hz1/2) was 1.89 times that of the single-pass configuration (3.4 fT/Hz1/2), consistent with the theoretical analysis. This study provides valuable theoretical guidance for analyzing the SNR performance of SERF atomic magnetometers and demonstrates the potential of multipass cells in enhancing their magnetic field sensitivity. The utilization of multipass cells presents a viable approach toward the realization of highly sensitive and portable miniaturized SERF atomic magnetometers.
The sensitive detection of either static or radio frequency (RF) magnetic fields is essential to many fundamental studies and applications. Here, we demonstrate the operation of a cold-atom-based RF magnetometer in performing 1D and 2D imaging of small metallic objects. It is based on a cold 85Rb atomic sample and operates in an unshielded environment with no active field stabilization. It shows a sensitivity up to 200 pT/Hz in the 5−35 kHz bandwidth range and can resolve a 0.4 mm wide cut in a 0.8 mm thick metallic foil. The characteristics of our system make it a good candidate for applications in civil and industrial surveillance.