Cross-polarization extinction enhancement and spin-orbit coupling of light for quantum-dot cavity-QED spectroscopy

TL;DR

This paper demonstrates a method to significantly improve cross-polarization extinction in quantum-dot cavity-QED spectroscopy by utilizing Fresnel birefringence and beam filtering, leading to enhanced single-photon contrast.

Contribution

It introduces an optimized approach combining birefringence and filtering to achieve a tenfold increase in polarization extinction for quantum dot spectroscopy.

Findings

Optimal single-reflection extinction enhancement observed.

Achieved 10x improvement in single-photon contrast.

Method applicable to resonant quantum dot excitation.

Abstract

Resonant laser spectroscopy is essential for the characterization, operation, and manipulation of single quantum systems such as semiconductor quantum dots. The separation of the weak resonance fluorescence from the excitation laser is key for high-quality single- and entangled photon sources. This is often achieved by cross-polarization laser extinction, which is limited by the quality of the optical elements. Recently, it was discovered that Fresnel-reflection birefringence in combination with single-mode filtering counteracting spin-orbit coupling effects enables a three-order of magnitude improvement of polarization extinction [PRX 11, 021007 (2021)]. Here, we first investigate multiple reflections and analyze beam reshaping, and observe that the single-reflection extinction enhancement is optimal. We then demonstrate this method for cross-polarization extinction enhancement for a resonantly excited semiconductor quantum dot in a birefringent optical micro cavity, and observe a 10x improvement of single-photon contrast.