Kee, Q. L., Zhao, L., Lecamwasam, R., Shajilal, B., Liang, X., Jose, J. K., Chen, Y., Lam, P. K., Wang, T. (2026). Spin correlations in recirculating multipass alkali cells for advancing quantum magnetometry. Optics and Lasers in Engineering, 204, 109828. https://doi.org/10.1016/j.optlaseng.2026.109828
Abstract:
Multipass cells enable long optical path lengths in compact volumes and are central to quantum technologies such as atomic magnetometers and optical quantum memories. In optical magnetometry, multipass geometries enhance sensitivity by increasing optical depth, reducing photon shot noise, and enabling quantum non-demolition detection. However, in conventional cylindrical multipass cells, Lissajous beam trajectories lead to repeated revisiting and incomplete mirror coverage, limiting effective volume utilization. Here we present a recirculating multipass alkali cell that overcomes these limitations by increasing the active-to-cell volume ratio and minimizing beam spot overlap. We develop an analytical ABCD-matrix model to predict beam trajectories, spot sizes, and astigmatism, validated by Zemax simulations. We further introduce a general analytical framework for spin correlation noise that incorporates astigmatism and spatial intensity distributions. By deriving the spin-noise time-correlation function and spectrum, we show how beam intensity profiles influence spin diffusion noise. Our results demonstrate improved beam coverage, reduced spot overlap, and enhanced spin correlation, particularly for concave mirrors with long focal lengths, while showing that avoiding tightly-focused regions significantly suppresses spin diffusion noise. These findings establish recirculating multipass cells as a practical, high-performance platform for precision atomic sensing and other multipass-cavity-based quantum devices.
License type:
Attribution 4.0 International (CC BY 4.0)
Funding Info:
This research / project is supported by the A*STAR - A*STAR Career Development Fund
Grant Reference no. : 222D800028
This research / project is supported by the A*STAR - Italy-Singapore Science and Technology Collaboration Grant
Grant Reference no. : R23I0IR042
This research / project is supported by the A*STAR - Delta-Q (Quantum Sensing)
Grant Reference no. : C230917004
This research / project is supported by the NRF - Competitive Research Program
Grant Reference no. : NRF-CRP30-2023-0002
This research is supported by core funding from: Q.InC Strategic Research and Translational Thrust
Grant Reference no. : Q.InC Strategic Research and Translational Thrust