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arXiv:2011.03785 · Physical Review A

Floquet description of optically pumped magnetometers

H. M. Florez, Tadas Pyragius

Published Mar 22, 2021• 5 citations
arXivHTMLPDF

Abstract

We present a theoretical description of the Voigt and Faraday effect based optically pumped magnetometers using the Floquet expansion. Our analysis describes the spin-operator dynamics of the first- $\stackrel{\ifmmode \hat{}\else \^{}\fi{}}{F}(t)$ and second-order ${\stackrel{\ifmmode \hat{}\else \^{}\fi{}}{F}}^{2}(t)$ moments and takes into account different pumping profiles and decoherence effects. We find that the theoretical results are consistent with previous experimental demonstrations over a wide range of fields and pumping conditions. Finally, the theoretical analysis presented here is generalized and can be extended to different magnetometry schemes with arbitrary pumping profiles and multiple radio-frequency fields.

DOI
10.1103/physreva.103.033113

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We present a theoretical description of the Voigt and Faraday effect based optically pumped magnetometers using the Floquet expansion. Our analysis describes the spin-operator dynamics of the first- F\ifmmode^\elseˆ\fi(t)\stackrel{\ifmmode \hat{}\else \^{}\fi{}}{F}(t)F\ifmmode^\elseˆ\fi​(t) and second-order F\ifmmode^\elseˆ\fi2(t){\stackrel{\ifmmode \hat{}\else \^{}\fi{}}{F}}^{2}(t)F\ifmmode^\elseˆ\fi​2(t) moments and takes into account different pumping profiles and decoherence effects. We find that the theoretical results are consistent with previous experimental demonstrations over a wide range of fields and pumping conditions. Finally, the theoretical analysis presented here is generalized and can be extended to different magnetometry schemes with arbitrary pumping profiles and multiple radio-frequency fields.
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The deterioration of spin coherence has been a significant challenge in the field of quantum magnetic measurements based on optically pumped atomic magnetometers (OPAMs). However, measurement and evaluation methods for specific relaxation components of OPAMs under working conditions remain lacking, which impedes further improvement in OPAM performance. To address this, we propose a methodology for quantifying the relaxation components of an OPAM under realistic operating conditions. Using this method, we confirm the existence of an anomalous relaxation mechanism induced by radio-frequency (RF) magnetic fields and develop an empirical expression to describe its behavior. The results experimentally demonstrate that, in addition to the well-known spin-exchange relaxation, the dominant contributions to spin relaxation arise from optical pumping and RF magnetic fields. This work paves the way for sensitivity enhancement in quantum magnetometry and refines the theoretical understanding of relaxation mechanisms in OPAMs.
We present a unified and easy-to-follow analytical framework based on the Bloch equations for deriving the small-signal frequency response of several common types of optically pumped magnetometers (OPMs). These include the Mx, light-shift dispersed Mz, Bell–Bloom, and RF (radio-frequency) types, as well as the class of unmodulated zero-field OPMs. It is shown that, depending on the operating regime, the frequency response of some of these magnetometers deviates significantly from the commonly assumed first-order filter behavior.
We present a theoretical study of the spectra produced by optical--radio-frequency double resonance devices, in which resonant linearly polarized light is used in the optical pumping and detection processes. We extend previous work by presenting algebraic results which are valid for atomic states with arbitrary angular momenta, arbitrary rf intensities, and arbitrary geometries. The only restriction made is the assumption of low light intensity. The results are discussed in view of their use in optical magnetometers.
Abstract Optically-pumped magnetometers (OPM) based on parametric resonance allow real-time tri-axial measurement of very small magnetic fields with a single optical access to the gas cell. Most of these magnetometers rely on circularly polarized pumping light. We focus here on the ones relying on linearly polarized light, yielding atomic alignment. For these magnetometers we investigate three second order effects which appear in the usual regimes of operation, so to clarify if they translate to metrological problems like systematic errors or increased noise. The first of these effects is the breakdown of the three-step approach when the optical beam has a large intensity. The second one is the breakdown of the rotating wave approximation when the frequencies of the RF fields are not much larger than the rates of other atomic processes. The third one is the tensor light-shift which appears when the light is slightly detuned from resonance. This work should help to clarify the accuracy reachable with OPM, which is an important question notably for medical imaging applications.
Optically pumped magnetometers usually rely on optical pumping using circularly or linearly polarized light. We study here zero-field magnetometers pumped with elliptically polarized light, preparing both atomic orientation and alignment with complementary geometries. We start by extending the three-step approach for elliptically polarized pumping. This allows us to study the Hanle effect in elliptical polarization by comparing the analytical absorption signals with experiments made on 4He^{4}\mathrm{He}4He metastable state. We then study parametric resonance magnetometers based on elliptical polarization by using the dressed-atom formalism with one and two radio-frequency fields. The results show good agreement with the experimental measurements and interesting perspectives for magnetometry where symmetry breaking by pumping light is mitigated.