Universal growth scheme for entanglement-ready quantum dots

TL;DR

This paper presents a universal growth method for quantum dots that emit entangled photons at telecom wavelengths with small fine-structure splitting, suitable for quantum networks, by employing droplet-epitaxy techniques.

Contribution

The authors develop a growth strategy that produces quantum dots with small FSS in the telecom band, compatible with optical cavities, using droplet-epitaxy on different substrates.

Findings

Quantum dots with 72% improved symmetry.

Mean FSS four times smaller than traditional Stranski-Krastanow QDs.

Successful emission at ~900nm and 1550nm wavelengths.

Abstract

Efficient sources of individual pairs of entangled photons are required for quantum networks to operate using fibre optic infrastructure. Entangled light can be generated by quantum dots (QDs) with naturally small fine-structure-splitting (FSS) between exciton eigenstates. Moreover, QDs can be engineered to emit at standard telecom wavelengths. To achieve sufficient signal intensity for applications, QDs have been incorporated into 1D optical microcavities. However, combining these properties in a single device has so far proved elusive. Here, we introduce a growth strategy to realise QDs with small FSS in the conventional telecom band, and within an optical cavity. Our approach employs droplet-epitaxy of InAs quantum dots on (001) substrates. We show the scheme improves the symmetry of the dots by 72%. Furthermore, our technique is universal, and produces low FSS QDs by molecular beam epitaxy on GaAs emitting at ~900nm, and metal-organic vapour phase epitaxy on InP emitting at 1550 nm, with mean FSS 4x smaller than for Stranski-Krastanow QDs.