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Séminaire « Propriétés optiques et électroniques des nanostructures » de l’INSP

Fundamental limits to photon coalescence and coherent scattering in quantum dot single-photon sources - Jake Iles-Smith, Jesper Mork - Mardi 31 mai 2016 à 14 h

INSP - 4 place Jussieu - 75252 PARIS Cedex 05 - Barre 22-32 - 2e étage, salle 201

Jake Iles-Smith and Jesper Mork - DTU Fotonik, Technical University of Denmark

Abstract

A semiconductor quantum dot embedded in a cavity or operating in the weak excitation limit dominated by coherent (elastic) scattering is a promising system for realizing solid-state sources that emit on-demand indistinguishable single-photons. Such sources are considered important for the development of quantum computers. However, phonons in the solid-state environment perturb the quantum dot energy levels, leading to decoherence and jeopardizing the indistinguishability of subsequently emitted photons.

In the talk we will discuss how the parameters characterizing the cavity-emitter system, like cavity quality factor and cavity-dot coupling strength, affect the rate of decoherence and the indistinguishability. It turns out that differences between phonon emission and phonon absorption probabilities lead to a “coloured” reservoir, where non-Markovian effects are important. Thus, simple approaches, where the dephasing is described by the common Lindblad-approach, fail in predicting how the indistinguishability depends on the characteristic parameters of the coupled system. Possibilities for reducing the rate of decoherence will be discussed.

In the regime of weak excitation dominated by coherent scattering, it is expected that the emitted photons benefit from a substantial suppression of detrimental interactions between the source and its solid-state (phonon) environment. Nevertheless, we demonstrate here that phonon interactions continue to play a prominent role in determining solid-state emission characteristics even for weak excitation. Specifically, we find that non-Markovian relaxation of the phonon environment leads to a fundamental limit to the fraction of coherently scattered light and to the visibility of two-photon coalescence at weak driving, both of which are absent within simpler Markovian treatments and atomic systems.