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# Spin damping in an rf atomic magnetometer

## Author(s): Alem, Orang; Sauer, Karen L; Romalis, Michael V

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 Abstract: Under negative feedback, the quality factor Q of a radio-frequency atomic magnetometer can be decreased by more than two orders of magnitude, so that any initial perturbation of the polarized spin system can be rapidly damped, preparing the magnetometer for detection of the desired signal. We find that noise is also suppressed under such spin damping, with a characteristic spectral response corresponding to the type of noise; therefore magnetic, photon shot, and spin-projection noise can be measured distinctly. While the suppression of resonant photon shot noise implies the closed-loop production of polarization-squeezed light, the suppression of resonant spin-projection noise does not imply spin squeezing, rather simply the broadening of the noise spectrum with Q. Furthermore, the application of spin damping during phase-sensitive detection suppresses both signal and noise in such a way as to increase the sensitivity bandwidth. We demonstrate a threefold increase in the magnetometer’s bandwidth while maintaining 0.3 fT/root Hz sensitivity. DOI: 10.1103/PhysRevA.87.013413 Publication Date: Jan-2013 Electronic Publication Date: 16-Jan-2013 Citation: Alem, Orang, Sauer, Karen L, Romalis, Mike V. (2013). Spin damping in an rf atomic magnetometer. PHYSICAL REVIEW A, 87 (10.1103/PhysRevA.87.013413 DOI: doi:10.1103/PhysRevA.87.013413 ISSN: 1050-2947 Type of Material: Journal Article Journal/Proceeding Title: PHYSICAL REVIEW A Version: Final published version. Article is made available in OAR by the publisher's permission or policy.

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