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Proceedings of SPIE, the International Society for Optical Engineering/Proceedings of SPIE

Entanglement in the biexciton cascade and the effect of pure dephasing

Pierce Munnelly, Alexander Carmele

Published Feb 9, 2012• 0 citations
Publisher

Abstract

The biexciton cascade within semiconductor quantum dots is known to be a useful source of polarizationentangled photon pairs. An analytical solution in the weak-coupling regime for quantum-state tomography matrix elements, i.e. the two-photon correlation function, is presented. It is demonstrated that with the inclusion of pure dephasing and considering degenerate exciton levels, the entanglement is not affected, and a convenient formula to calculate the degree of entanglement in an experiment is derived.

DOI
10.1117/12.906572

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The biexciton cascade within semiconductor quantum dots is known to be a useful source of polarizationentangled photon pairs. An analytical solution in the weak-coupling regime for quantum-state tomography matrix elements, i.e. the two-photon correlation function, is presented. It is demonstrated that with the inclusion of pure dephasing and considering degenerate exciton levels, the entanglement is not affected, and a convenient formula to calculate the degree of entanglement in an experiment is derived.
A fundamental approach to generate polarization-entangled photon pairs from solid-state devices is the biexciton cascade in semiconductor quantum dots. For efficient photon pair generation in the weak coupling regime, we present an analytical solution for the two-photon matrix elements (quantum-state tomography), including dephasing and relaxation mechanisms. In particular, we show that a pure dephasing mechanism does not affect the degree of entanglement for quantum dots with degenerated exciton levels.
We develop a theoretical model to study the intensity–intensity correlation of polarization-entangled photons emitted in a biexciton–exciton cascade. We calculate the degree of correlation and show how polarization correlations are affected by the presence of dephasing and energy-level splitting of the excitonic states. Our theoretical calculations are in agreement with the recent observation of polarization-dependent intensity–intensity correlations from a single semiconductor quantum dot (Stevenson et al 2006 Nature 439 179). Our model can be extended to study polarization-entangled photon emission in coupled quantum dot systems.
Abstract. We develop a theoretical model to study the Intensity-Intensity correlation of polarization entangled photons emitted in a biexciton-exciton cascade. We calculate the degree of correlation and show how polarization correlation are affected by the presence of dephasing and energy level splitting of the excitonic states. Our theoretical calculations are in agreement with the recent observation of polarization dependent Intensity-Intensity correlations from a single semiconductor quantum dot [R. M. Stevenson et. al. Nature 439, 179 (2006)]. Our model can be extended to study polarization entangled photon emission in coupled quantum dot systems. PACS numbers: 03.67.bg,42.50.Ar,42.50.CtNonclassical Correlation of Polarization Entangled Photons in a Biexciton-Exciton Cascade2 1.
We theoretically investigate the production of polarization-entangled photons through the biexciton cascade decay in a single semiconductor quantum dot. To accomplish a high degree of entanglement, despite the exciton fine-structure splitting, one must either energetically align the two exciton states by means of external fields or erase the which-path information by postselection or time reordering of photons. Here we show that in the latter schemes the photon state becomes deteriorated through dephasing processes in the solid, and the degree of entanglement remains low.
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We compute the concurrence of the polarization-entangled photon pairs generated by the biexciton cascade decay of a semiconductor quantum dot. We show how a cavity-induced increase of the photon emission rate reduces the effect of dot dephasing and excitonic fine structure on the concurrence. However, strong dot-cavity couplings, as well as low detection efficiencies, increase the detrimental effect of multiple cascades. This affects the merits of the entangled photon-pair source, beyond what is estimated by quantum tomography.