[2603.28421] Learning unified control of internal spin squeezing in atomic qudits for magnetometry

Quantum Physics arXiv:2603.28421 (quant-ph) [Submitted on 30 Mar 2026] Title:Learning unified control of internal spin squeezing in atomic qudits for magnetometry Authors:C. Z. Cao, J. Z. Han, M. Xiong, M. Deng, L. Wang, X. Lv, M. Xue View a PDF of the paper titled Learning unified control of internal spin squeezing in atomic qudits for magnetometry, by C. Z. Cao and 6 other authors View PDF HTML (experimental) Abstract:Generating and preserving metrologically useful quantum states is a central challenge in quantum-enhanced atomic magnetometry. In multilevel atoms operated in the low-field regime, the nonlinear Zeeman (NLZ) effect is both a resource and a limitation. It nonlinearly redistributes internal spin fluctuations to generate spin-squeezed states within a single atomic qudit, yet under fixed readout it distorts the measurement-relevant quadrature and limits the accessible metrological gain. This challenge is compounded by the time dependence of both the squeezing axis and the effective nonlinear action. Here we show that physics-informed reinforcement learning can transform NLZ dynamics from a source of readout degradation into a sustained metrological resource. Using only experimentally accessible low-order spin moments, a trained agent identifies, in the $f=21/2$ manifold of $^{161}\mathrm{Dy}$, a unified control policy that rapidly prepares strongly squeezed internal states and stabilizes more than $4\,\mathrm{dB}$ of fixed-axis spin squeezing under always-on NL...