Coherent polarization self-rotation
Phys. Rev. A 113, 043715 – Published 8 April, 2026
DOI: https://doi.org/10.1103/3m6y-sfx8
Abstract
We introduce and study coherent polarization self-rotation (CPSR), a two-photon light-matter interaction in dense alkali-metal vapors that enables both narrowband optical spectroscopy of magnetic transitions and coherent coupling between light and collective atomic spins. Unlike conventional polarization self-rotation, CPSR requires initial spin polarization and a predominantly linearly polarized probe. It operates efficiently even in optically thick vapors with high buffer-gas pressure, rapid spin-exchange collisions, and optically unresolved hyperfine structure. We demonstrate CPSR with near-unity contrast in rubidium and achieve an exceptionally narrow two-photon linewidth of 10 Hz in potassium. CPSR realizes a coherent interface between one optical quadrature and the long-lived collective electronic spin, offering a robust and scalable spin-light coupling in optically thick platforms. This opens opportunities for quantum optics, including quantum-enhanced metrology in the audio-frequency band and coherent transduction between light and ultralong-lived noble-gas spins via alkali-metal spins.
