Cavity-enhanced polarization rotation measurements for low-disturbance probing of atoms

TL;DR

This paper introduces a cavity-enhanced polarization rotation technique to improve magnetic effect detection in transparent media with minimal disturbance, demonstrating theoretical analysis and experimental validation with atomic ensembles.

Contribution

It presents a novel cavity-enhanced measurement method for polarization rotation, showing improved sensitivity and simplicity over traditional approaches.

Findings

Enhanced Faraday rotation detection in atomic ensembles

Demonstrated shot-noise-limited sensitivity

Theoretical predictions match experimental results

Abstract

We propose and demonstrate cavity-enhanced polarization-rotation measurement as a means to detect magnetic effects in transparent media with greater sensitivity at equal optical disturbance to the medium. Using the Jones calculus, we compute the effective polarization rotation effect in a Fabry-Perot cavity containing a magnetic medium, including losses due to enclosure windows or other sources. The results show that when measuring polarization rotation, collecting the transmitted light has advantages in simplicity and linearity relative to collecting the reflected light. We demonstrate the technique by measuring Faraday rotation in a $^{87}$Rb atomic ensemble in the single-pass and cavity-enhanced geometries, and observe enhancement in good agreement with the theoretical predictions. We also demonstrate shot-noise-limited operation of the enhanced rotation scheme in the small-angle regime.