Magic-wavelength Faraday probe measures spin continuously and without light shifts
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 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 {\mu}G accuracy every 5 ms; or equivalently makes > 200 successive measurements each at sensitivity.
Keywords
Cite
@article{arxiv.1705.10965,
title = {Magic-wavelength Faraday probe measures spin continuously and without light shifts},
author = {M. Jasperse and M. J. Kewming and S. N. Fischer and P. Pakkiam and R. P. Anderson and L. D. Turner},
journal= {arXiv preprint arXiv:1705.10965},
year = {2017}
}