A scheme of the magnetometer that simultaneously employs M X and M R magnetic resonance signals with the latter signal related to the radial component of the rotating atomic magnetic moment is proposed and tested. With respect to the shape, dynamic characteristics, and metrological parameters, the M R signal is similar to the M X signal that is widely used in magnetometry but the former signal can be detected simultaneously with the M X signal using a common radio optical scheme. The proposed device represents a fast M X magnetometer with the phase in the feedback loop that is controlled by a slow precise M R magnetometer implemented using the same atoms. The device that can be based on a conventional M X sensor simultaneously exhibits a relatively short response time (τ ≤ 0.1 s) and the accuracy that is approximately equal to the resolution of the quantum M X discriminator at times of 10–100 s. The scheme is experimentally tested, and the statistic estimate of reproducibility is (1.2 ± 1.1) pT.
A scheme of the magnetometer that simultaneously employs M X and M R magnetic resonance signals with the latter signal related to the radial component of the rotating atomic magnetic moment is proposed and tested. With respect to the shape, dynamic characteristics, and metrological parameters, the M R signal is similar to the M X signal that is widely used in magnetometry but the former signal can be detected simultaneously with the M X signal using a common radio optical scheme. The proposed device represents a fast M X magnetometer with the phase in the feedback loop that is controlled by a slow precise M R magnetometer implemented using the same atoms. The device that can be based on a conventional M X sensor simultaneously exhibits a relatively short response time (τ ≤ 0.1 s) and the accuracy that is approximately equal to the resolution of the quantum M X discriminator at times of 10–100 s. The scheme is experimentally tested, and the statistic estimate of reproducibility is (1.2 ± 1.1) pT.
The new scheme of a combined quantum magnetometric device is proposed that represents a fast M X magnetometer, in which the phase of M X signal detection is corrected with respect to the maximum of the variable component of the atomic magnetic moment. The device combines a high response speed (τ ≤ 0.1 s) with high precision, which is determined by the resolving power of the quantum M X magnetometer for a time of an order of 100 s. The reproducibility of field measurements is on a level of 2–3 pT.
Introduction Shortly after the inception of atomic magnetometry, alkali-vapor magnetometers were being used to measure the Earth's magnetic field to unprecedented precision. During the same era, Bell and Bloom first demonstrated all-optical atomic magnetometry through synchronous optical pumping [1] (see Chapters 1 and 6). In this approach, optical-pumping light is frequency- or amplitude-modulated at harmonics of the Larmor frequency ω L to generate a precessing spin polarization within an alkali vapor at finite magnetic field [2, 3]. Although this technique received considerable attention from the atomic physics community for its applicability to optical pumping experiments, Earth's-field alkali-vapor atomic magnetometers continued to rely on radiofrequency (RF) field excitation for several decades (see Chapter 4). Upon the advent of diode lasers addressing alkali and metastable helium transitions, synchronously pumped magnetometers experienced a revival beginning in the late 1980s. In recent years, such magnetometers have found applications in nuclear magnetic resonance detection [4] (see also Chapter 14), quantum control experiments [5], and chip-scale devices intended for spacecraft use [6] (see also Chapters 7 and 15). All-optical magnetometers possess several advantages over devices that employ RF coils. RF-driven magnetometers can suffer from cross-talk if two sensors are placed in close proximity, since the AC magnetic field driving resonance in one vapor cell can adversely affect the other. All-optical magnetometers are free from such interference. When operated in self-oscillating mode [7], RF-driven magnetometers require an added ±90° electronic phase shift in the feedback loop to counter the intrinsic phase shift between the RF field and the probe-beam modulation.
We report a rubidium atomic magnetometer based on pump-probe nonlinear magneto-optical rotation. The rubidium vapor cell is placed in a five-layer magnetic shield with inner coils that can generate uniform magnetic fields along the direction of pump beam, and the cell is also placed in the center of a Helmholtz coil that can generate an oscillating magnetic field perpendicular to the direction of pump beam. The atoms are optically pumped by circularly polarized pump beam along a constant magnetic field in a period of time, then the pump beam is turned off and a /2 pulse of oscillating magnetic field for 87Rb atoms is applied. After the above process, the individual atomic magnetic moments become phase coherent, resulting in a transverse magnetization vector precessing at the Larmor frequency in the magnetic field. The linearly polarized probing beam is perpendicular to the direction of magnetic field, and can be seen as a superposition of the left and right circularly polarized light. Because of the different absorptions and dispersions of the left and right circularly polarized light by rubidium atoms, the polarization direction of probing beam rotates when probing beam passes through rubidium vapor cell. The rotation of the polarization is subsequently converted into an electric signal through a polarizing beam splitter. Finally, the decay signal related to the transverse magnetization vector is measured. The Larmor frequency proportional to magnetic field is obtained by the Fourier transform of the decay signal. The value of magnetic field is calculated from the formula:B=(2/) f, where and f are the gyromagnetic ratio and Larmor frequency, respectively. In order to measure the magnetic field in a wide range, the tracking lock mode is proposed and tested. The atomic magnetometer can track the magnetic field jump of 1000 nT or 10000 nT, indicating that the atomic magnetometer has strong locking ability and can be easily locked after start-up. The main performances in different magnetic fields are tested. The results show that the measurement range of the atomic magnetometer is from 100 nT to 100000 nT, the extreme sensitivity is 0.2 pT/Hz1/2, and the magnetic field resolution is 0.1 pT. The transverse relaxation times of the transverse magnetization vector in different magnetic fields are obtained, and the relaxation time decreases with the increase of the magnetic field. When the measurement range is from 5000 nT to 100000 nT, the magnetic field sampling rate of the atomic magnetometer can be adjusted in a range from 1 Hz to 1000 Hz. The atomic magnetometer in high sampling rate can measure weak alternating magnetic field at low frequency. This paper provides an important reference for developing the atomic magnetometer with large measurement range, high sensitivity and high sampling rate.
We show, theoretically and experimentally, how the absolute orientation and polarization state of radio-frequency (rf) magnetic fields in a transverse two-dimensional (2D) plane can be uniquely determined using two optically pumped atomic magnetometers. In addition, the output signals from these quantum sensors can be readily expressed as a magnetic Jones vector. This composite device can complement electric field detection in finding rf directions or it can be used in applications where the electric field is negligible. The latter is found in a myriad of applications where the source can be modeled as radiating magnetic dipoles in the near-field limit. This tool could be used to characterize the response of a material to rf excitation or to distinguish signal from noise.
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.
The operation of basic types of quantum magnetometers with optical pumping as signal receivers in the ultra-long wavelength range is demonstrated in this work. The circuit realization of an experimental setup, provides the registration of double radio-optical resonance signals, is discussed. The realized magnetometers sensitivity is tens of pT/Hz1/2at bandwidth up to 1 kHz. The comparison of the absorption resonance signals in operation modes of quantum magnetometers with and without of synchronous detection is done. Maximum frequency of magnetic signals is about 534 Hz. An estimate of the maximum receiving distance is about of 100 m. The spectrum of frequency-modulated magnetometer signal is discussed. Prospects and features for the use of quantum magnetometers as super-low-frequency signal receivers are presented.