Calibration of Spin-Light Coupling by Coherently Induced Faraday Rotation

TL;DR

This paper introduces a calibration method using Coherently Induced Faraday Rotation (CIFAR) to accurately measure light-matter coupling strength in spin oscillators, applicable in various experimental setups without altering existing conditions.

Contribution

The paper presents a novel CIFAR-based technique for calibrating spin-light coupling rates that is independent of detection efficiency and adaptable to continuous or pulsed measurements.

Findings

Successfully calibrated coupling rate in warm cesium vapor

Method is robust against detection quantum efficiency variations

Applicable to both continuous and pulsed measurement regimes

Abstract

Calibrating the strength of the light-matter interaction is an important experimental task in quantum information and quantum state engineering protocols. The strength of the off-resonant light-matter interaction in multi-atom spin oscillators can be characterized by the coupling rate $\Gamma_\text{S}$. Here we utilize the Coherently Induced Faraday Rotation (CIFAR) signal for determining the coupling rate. The method is suited for both continuous and pulsed readout of the spin oscillator, relying only on applying a known polarization modulation to the probe laser beam and detecting a known optical polarization component. Importantly, the method does not require changes to the optical and magnetic fields performing the state preparation and probing. The CIFAR signal is also independent of the probe beam photo-detection quantum efficiency, and allows direct extraction of other parameters of the interaction, such as the tensor coupling $\zeta_\text{S}$, and the damping rate $\gamma_\text{S}$. We verify this method in the continuous wave regime, probing a strongly coupled spin oscillator prepared in a warm cesium atomic vapour.