Extended linear regime of cavity-QED enhanced optical circular birefringence induced by a charged quantum dot

TL;DR

This paper explores the limits of linear optical effects like Faraday rotation and birefringence in cavity-QED systems with quantum dots, showing their robustness at certain power levels and implications for quantum information processing.

Contribution

It extends the understanding of the linear regime of cavity-QED effects by analyzing the transition to saturation and comparing semiclassical and quantum models.

Findings

GFR and GCB are input-field independent at intermediate powers in the strong coupling regime.

Dressed state resonances are sensitive to input power and not well described by semiclassical approximation.

Linear effects enable rapid, robust readout of single electron spins and high-speed quantum gates.

Abstract

Giant optical Faraday rotation (GFR) and giant optical circular birefringence (GCB) induced by a single quantum-dot spin in an optical microcavity can be regarded as linear effects in the weak-excitation approximation if the input field lies in the low-power limit [Hu et al, Phys.Rev. B {\bf 78}, 085307(2008) and ibid {\bf 80}, 205326(2009)]. In this work, we investigate the transition from the weak-excitation approximation moving into the saturation regime comparing a semiclassical approximation with the numerical results from a quantum optics toolbox [S.M. Tan, J. Opt. B {\bf 1}, 424 (1999)]. We find that the GFR and GCB around the cavity resonance in the strong coupling regime are input-field independent at intermediate powers and can be well described by the semiclassical approximation. Those associated with the dressed state resonances in the strong coupling regime or merging with the cavity resonance in the Purcell regime are sensitive to input field at intermediate powers, and cannot be well described by the semiclassical approximation due to the quantum dot saturation. As the GFR and GCB around the cavity resonance are relatively immune to the saturation effects, the rapid read out of single electron spins can be carried out with coherent state and other statistically fluctuating light fields. This also shows that high speed quantum entangling gates, robust against input power variations, can be built exploiting these linear effects.