Intrinsic Quantum Noise in Faraday Rotation Measurements of a Single Electron Spin

TL;DR

This paper provides a fully quantum-mechanical analysis of Faraday rotation in quantum dots, revealing intrinsic quantum noise that limits measurement sensitivity and proposing a method to assess spin state purity.

Contribution

It introduces a quantum model for Faraday rotation that accounts for entanglement-induced noise, advancing understanding of measurement limits in quantum dot spin detection.

Findings

Intrinsic quantum noise sets fundamental sensitivity limits.

Quantum entanglement affects Faraday rotation measurements.

Proposes a method to measure spin state purity.

Abstract

Faraday rotation is one way to realize quantum non-demolition measurement of electron spin in quantum dots. To describe Faraday rotation, semiclassical models are typically used, based on quantized electron spin states and classical electromagnetic fields. Such treatments neglect the entanglement between electronic and photonic degrees of freedom that produce intrinsic quantum noise, limiting the ultimate sensitivity of this technique. We present a fully quantum-mechanical description of Faraday rotation, and quantify this intrinsic noise. A method for measuring the purity of a given spin state is suggested based on this analysis.