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  • Letter
  • Open Access

Continuous cloud position spectroscopy using a magneto-optical trap

Benedikt Heizenreder1,*, Ananya Sitaram1,*, Sana Boughdachi1,2, Andrew von Hörsten2, Yan Xie3, Andreas Brodschelm2, and Florian Schreck1,4,†

  • *These authors contributed equally to this work.
  • †Contact author: CloudPositionSpectroscopy@strontiumBEC.com
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Phys. Rev. Applied 25, L031003 – Published 17 March, 2026

DOI: https://doi.org/10.1103/wdp6-98wh

Abstract

We demonstrate a continuous spectroscopy technique with frequency sensitivity well below the natural transition linewidth, while maintaining a locking range hundreds of times larger. The method exploits the position dependence of a continuous, broadband magneto-optical trap (MOT) operating on the 7.5-kHz-wide intercombination line of strontium. We show that the frequency sensitivity is fundamentally insensitive to the effective MOT laser linewidth. By applying active feedback on the MOT position to a dispersion-optimized frequency comb, which serves as the reference for stabilizing the MOT laser (Boughdachi et al., arXiv:2507.23617), we achieve a frequency instability below 4.4×10−13 after 400 s of averaging in both the optical and radio-frequency domains, surpassing the performance of conventional hot-vapor modulation transfer spectroscopy. Our method is a broadly applicable alternative route to frequency references in the high 10−14 range around 100 s.

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Phys. Rev. Applied 25, L031003– Published 17 March, 2026
  • Received 9 September 2025
  • Revised 14 November 2025
  • Accepted 18 February 2026
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Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI.

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