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arXiv:2106.13360 · Physical Review Letters

Atomic Compass: Detecting 3D Magnetic Field Alignment with Vector Vortex Light

Francesco Castellucci, Thomas W. Clark, Adam Selyem, Jinwen Wang, Sonja Franke‐Arnold

Published Nov 30, 2021• 80 citations
arXivHTMLPDF

Abstract

We describe and demonstrate how 3D magnetic field alignment can be inferred from single absorption images of an atomic cloud. While optically pumped magnetometers conventionally rely on temporal measurement of the Larmor precession of atomic dipoles, here a cold atomic vapor provides a spatial interface between vector light and external magnetic fields. Using a vector vortex beam, we inscribe structured atomic spin polarization in a cloud of cold rubidium atoms and record images of the resulting absorption patterns. The polar angle of an external magnetic field can then be deduced with spatial Fourier analysis. This effect presents an alternative concept for detecting magnetic vector fields and demonstrates, more generally, how introducing spatial phases between atomic energy levels can translate transient effects to the spatial domain.

DOI
10.1103/physrevlett.127.233202

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We describe and demonstrate how 3D magnetic field alignment can be inferred from single absorption images of an atomic cloud. While optically pumped magnetometers conventionally rely on temporal measurement of the Larmor precession of atomic dipoles, here a cold atomic vapor provides a spatial interface between vector light and external magnetic fields. Using a vector vortex beam, we inscribe structured atomic spin polarization in a cloud of cold rubidium atoms and record images of the resulting absorption patterns. The polar angle of an external magnetic field can then be deduced with spatial Fourier analysis. This effect presents an alternative concept for detecting magnetic vector fields and demonstrates, more generally, how introducing spatial phases between atomic energy levels can translate transient effects to the spatial domain.
At Glasgow we routinely use a variety of techniques to imprint structure in the spatial amplitude, phase and polarization of a light beam. This allows us to generate vector vortex beams at high fidelity, with applications in polarimetry and strong focusing. Vector vortex beams can also induce magnetic dipole moments in an atomic medium, in our case rubidium atoms at 100 micro Kelvin, with an orientation that depends on the local polarization direction. This affects, in a nontrivial manner, the propagation of the structured light field through the atomic medium, dependent on an external magnetic field. We show that we can retrieve the orientation of the magnetic field from the absorption of the structured light - an atomic compass.
Abstract The relationship between the magnetic field direction and the spatial intensity distribution of a radially polarized light passing through a polarized thermal atom ensemble is investigated, which is intuitively presented in a polarization selection absorption effect of thermal atoms. The radially polarized light has a spatial axisymmetric polarization structure, which is set as the probe beam. If the direction of the applied magnetic field is transformed, the absorption of the alignment atomic system to special polarization components of the probe light is changed, resulting in a different absorption ratio. This allows the 3D vector direction of the magnetic field to be inferred by using only the absorption ratio and the projection coefficient of the transmission intensity pattern. Based on this, this work provides a compass based on a thermal atom system, demonstrating a new method for measuring the magnetic field direction in space.
Absorption profiles of vector light upon interaction with atomic vapor carries distinct signatures of an external magnetic field vector. However, this signature becomes ambiguous for antiparallel magnetic field vectors of equal magnitude, which makes their absorption profiles visually indistinguishable. To resolve this ambiguity, we present a theoretical analysis of the interaction of vector light with optically polarized atoms immersed in reference and test magnetic fields. Furthermore, we demonstrate the complete characterization of the arbitrarily oriented test magnetic field via a Fourier analysis of the absorption profile. This analysis reveals a one-to-one correspondence between the magnetic field properties and the profile's contrast and rotational angle. Our findings open an avenue to design an optical vector atomic magnetometer based on structured light fields.
We present a magnetic field imaging technique based on spatially resolved detection of Larmor precession. An optically trapped, elongated, and cold atomic sample of rubidium serves as magnetic field probe. We detect Larmor precession with a spatial and a temporal resolution of ∼50μm and ∼120μs, respectively. Projection-noise limited absorption imaging, feasible with current technologies, implies a sensitivity of ∼10pT/Hz at 50μm resolution; addition of an optical lattice could give ∼300fT/Hz sensitivity.
We describe a method to dispersively detect all three vector components of an external magnetic field using alkali atoms based on the Voigt effect. Our method relies on measuring the linear birefringence of the radio frequency dressed atomic medium via polarization homodyning. This gives rise to modulated polarization signals at the first and second harmonic of the dressing frequency. The vector components of the external magnetic field are mapped onto the quadratures of these harmonics. We find that our scheme can be utilised in both cold and hot atomic gases to detect such external fields in shielded and unshielded environments. In the shielded hot vapour case we achieve field sensitivities well below 1~pT/√ Hz range for all 3 vector components, using pump-probe cycles with 125 Hz repetition rate, and limited by the short coherence time of the cell. Finally, our scheme has a simple single axis beam geometry making it advantageous for miniature magnetic field sensors.
We propose and demonstrate an experimental implementation for the observation of magnetic fields from spatial features of absorption profiles in a warm atomic vapor. A radially polarized vector beam that traverses atomic vapor will generate an absorption pattern with a petal-like structure by the mediation of a transverse magnetic field (TMF). The spatial absorption pattern rotates when the azimuthal angle of the TMF is changed, while its contrast decreases when the longitudinal component of the magnetic field increases. By analyzing the intensity distribution of the transmitted pattern, we can determine the magnetic field strength. Our work provides a framework for investigating 3D magnetic field distributions based on atoms.