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arXiv · 1705.10965

Magic-wavelength Faraday probe measures spin continuously and without light shifts

M. Jasperse·M. J. Kewming·S. N. Fischer·P. Pakkiam·R. P. Anderson·L. D. Turner
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Abstract

We describe a dispersive Faraday optical probe of atomic spin which performs a weak measurement of spin projection of a quantum gas continuously for more than one second. To date focusing bright far-off-resonance probes onto quantum gases has proved invasive, due to strong scalar and vector light shifts exerting dipole and Stern-Gerlach forces. We show that tuning the probe near the magic-zero wavelength at 790 nm between the fine-structure doublet of $^{87}$Rb cancels the scalar light shift, and careful control of polarization eliminates the vector light shift. Faraday rotations due to each fine-structure line reinforce at this wavelength, enhancing the signal-to-noise ratio for a fixed rate of probe-induced decoherence. Using this minimally-invasive spin probe we perform microscale atomic magnetometry at high temporal resolution. Spectrogram analysis of the Larmor precession signal of a single spinor Bose-Einstein condensate measures a time-varying magnetic field strength with 1 μG accuracy every 5 ms; or equivalently makes > 200 successive measurements each at $10\,\mathrm{pT/\sqrt{Hz}}$ sensitivity.

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M. Jasperse, M. J. Kewming, S. N. Fischer, P. Pakkiam, R. P. Anderson, L. D. Turner. 2017-05-31. Magic-wavelength Faraday probe measures spin continuously and without light shifts. https://doi.org/10.1103/physreva.96.063402

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