Highly indistinguishable and strongly entangled photons from symmetric GaAs quantum dots

Abstract

The development of scalable sources of non-classical light is fundamental to unlocking the technological potential of quantum photonics. Semiconductor quantum dots are emerging as near-optimal sources of indistinguishable single photons. However, their performance as sources of entangled-photon pairs are still modest compared to parametric down converters. Photons emitted from conventional Stranski–Krastanov InGaAs quantum dots have shown non-optimal levels of entanglement and indistinguishability. For quantum networks, both criteria must be met simultaneously. Here, we show that this is possible with a system that has received limited attention so far: GaAs quantum dots. They can emit triggered polarization-entangled photons with high purity (g(2)(0) = 0.002±0.002), high indistinguishability (0.93±0.07 for 2 ns pulse separation) and high entanglement fidelity (0.94±0.01). Our results show that GaAs might be the material of choice for quantum-dot entanglement sources in future quantum technologies.

Building Blocks for Quantum Network Based on Group‐IV Split‐Vacancy Centers in Diamond

“…Quantum bit (qubit), as the fundamental building block for quantum computing and quantum network, can take various materialized forms in reality as long as the system comprises two distinct quantum states that can be coherently superpositioned, for example, the atomic clock states of trapped ion, the orthogonal polarization states of photon, the spin states of electron confined in a solid‐state potential, the superconducting state of micro‐circuit, and the emergent Majorana bound states featuring topological protection . All these candidates possess a finite coherence time imposed by the dephasing processes originating from the inevitable coupling to the host environment.…”

Advanced Technologies for Quantum Photonic Devices Based on Epitaxial Quantum Dots

“…Thanks to the Coulomb interaction between the QD‐confined charges, the X energy is typically separated from the XX energy by a few meV. The pump laser energy is thus not resonant with either line and can be effectively suppressed with sharp notch filters . Recent studies have shown that the X and XX can be coherently populated with near‐equal efficiencies, showing entanglement fidelities comparable to that of SPDC sources .…”

“…d) Cross‐sectional 3D view of an AFM image of a nanohole in an AlGaAs layer, along with the sketch of the sample structure and the top view of the AFM measurement result; e–f) microphotoluminescence spectrum of a representative QD under non‐resonant excitation (e) and resonant two‐photon excitation (f). Reproduced with permission . Copyright 2017, Springer Nature.…”

“…were the first to demonstrate that droplet‐etched GaAs/AlGaAs QDs can display an ultra‐small FSS, with an average of 4 µeV . The very small FSS combined with a short radiative lifetime of a few 100 ps allow the ideal lifetime‐limited linewidth of ≈5 µeV of the exciton emission close to the value of the FSS, resulting in single pairs of entangled photons emission with an ultra‐high purity and high degree of entanglement without any postgrowth tuning techniques . Additionally, they can generate single‐photons with emission wavelength around 780 nm under both non‐resonant excitation (Figure e) and resonant two‐photon excitation (Figure (f)).…”

Interfacing a quantum dot with a spontaneous parametric down-conversion source

“…An alternative approach is to pursue intracavity SPDC as discussed in the introduction, but we believe that a better option is to use even shorter lifetime quantum dots such as the GaAs/AlGaAs system, where quantum dots are grown by droplet epitaxy. Early results show radiative lifetimes of less than 250 ps [26,27] and high indistinguishability without any filtering or shaping. Table 1.…”