Highly indistinguishable and strongly entangled photons from symmetric GaAs quantum dots

TLDR

Scalable sources of non‑classical light are essential for quantum photonics, and semiconductor quantum dots are promising but currently provide only modest entanglement and indistinguishability for entangled‑photon pair generation. This study demonstrates that droplet‑etched GaAs quantum dots can simultaneously produce highly indistinguishable and strongly entangled photon pairs. Using a two‑photon resonant excitation scheme, the authors trigger polarization‑entangled photons from GaAs quantum dots, achieving high purity (g^(2)(0)=0.002), indistinguishability (0.93), and fidelity (0.94). The emitted photons violate Bell’s inequality (2.64) without filtering, achieving near‑unity entanglement and indicating GaAs as the preferred platform for future quantum technologies.

Abstract

The development of scalable sources of non-classical light is fundamental to unlock the technological potential of quantum photonics\cite{Kimble:Nat2008}. Among the systems under investigation, semiconductor quantum dots are currently emerging as near-optimal sources of indistinguishable single photons. However, their performances as sources of entangled-photon pairs are in comparison still modest. Experiments on conventional Stranski-Krastanow InGaAs quantum dots have reported non-optimal levels of entanglement and indistinguishability of the emitted photons. For applications such as entanglement teleportation and quantum repeaters, both criteria have to be met simultaneously. In this work, we show that this is possible focusing on a system that has received limited attention so far: GaAs quantum dots grown via droplet etching. Using a two-photon resonant excitation scheme, we demonstrate that these quantum dots can emit triggered polarization-entangled photons with high purity (g^(2)(0)=0.002 +/-0.002), high indistinguishability (0.93 +/-0.07) and high entanglement fidelity (0.94 +/-0.01). Such unprecedented degree of entanglement, which in contrast to InGaAs can theoretically reach near-unity values, allows Bell's inequality (2.64 +/-0.01) to be violated without the aid of temporal or spectral filtering. Our results show that if quantum-dot entanglement resources are to be used for future quantum technologies, GaAs might be the system of choice.