Suppressing phonon decoherence of high performance single-photon sources in nanophotonic waveguides

TL;DR

This paper demonstrates that applying a low refractive index cladding to nanophotonic waveguides significantly suppresses phonon-induced decoherence in quantum-dot single-photon sources, greatly enhancing photon indistinguishability.

Contribution

It introduces a method to reduce phonon decoherence in quantum-dot sources by cladding waveguides, improving photon coherence and enabling efficient fiber coupling.

Findings

Photon indistinguishability approaches unity with cladding

Decoherence is suppressed by waveguide cladding

Photon extraction efficiency is improved

Abstract

The fundamental process limiting the coherence of quantum-dot based single-photon sources is the interaction with phonons. We study the effect of phonon decoherence on the indistinguishability of single photons emitted from a quantum dot embedded in a suspended nanobeam waveguide. At low temperatures, the indistinguishability is limited by the coupling between the quantum dot and the fundamental vibrational modes of the waveguide and is sensitive to the quantum-dot position within the nanobeam cross-section. We show that this decoherence channel can be efficiently suppressed by clamping the waveguide with a low refractive index cladding material deposited on the waveguide. With only a few microns of cladding material, the coherence of the emitted single photons is drastically improved. We show that the degree of indistinguishability can reach near unity and become independent of the quantum-dot position. We finally show that the cladding material may serve dual purposes since it can also be applied as a means to efficiently outcouple single photons from the nanophotonic waveguide into an optical fiber. Our proposal paves the way for a highly efficient fiber-coupled source of indistinguishable single photons based on a planar nanophotonic platform.