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arXiv:2509.07736 · Physical Review Applied

Continuous cloud position spectroscopy using a magneto-optical trap

Benedikt Heizenreder, Ananya Sitaram, Sana Boughdachi, Andrew von Hörsten, Yan Xie, Andreas Brodschelm, Florian Schreck

Published Feb 18, 2026• 0 citations
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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 , 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.

DOI
10.1103/wdp6-98wh

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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 , 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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In this paper, we present a technique for magneto-optical cooling and trapping of neutral atoms using a single laser. The alternating-frequency magneto-optical trap (AF-MOT) uses an agile light source that sequentially switches between cooling and repumping transition frequencies by tuning the injection current of the laser diode. We report on the experimental demonstration of such a system for 87Rb and 85Rb based on a microintegrated extended cavity diode laser performing laser frequency jumps of up to 6.6 GHz with a tuning time in the microsecond regime and a repetition rate of up to 7.6 kHz. For that, a combination of a feed-forward for coarse frequency control and a feedback for precise locking was used. We discuss the results of the AF-MOT characterization in terms of atom numbers and cloud temperature for different operation parameters.