On-demand generation of background--free single photons from a solid-state source

TL;DR

This paper reports a solid-state single-photon source with an unprecedentedly low second-order coherence, achieved through two-photon excitation and advanced filtering, promising significant improvements for quantum information applications.

Contribution

The authors demonstrate the lowest reported $g^{(2)}(0)$ for a single-photon source using GaAs/AlGaAs quantum dots with two-photon excitation and ultralow dark-count detectors.

Findings

Achieved $g^{(2)}(0) = (7.5 imes 10^{-5})$ without background subtraction.

Used two-photon excitation to suppress re-excitation.

Implemented ultralow dark-count detectors for minimal false coincidences.

Abstract

True on--demand high--repetition--rate single--photon sources are highly sought after for quantum information processing applications. However, any coherently driven two-level quantum system suffers from a finite re-excitation probability under pulsed excitation, causing undesirable multi--photon emission. Here, we present a solid--state source of on--demand single photons yielding a raw second--order coherence of $g^{(2)}(0)=(7.5\pm1.6)\times10^{-5}$ without any background subtraction nor data processing. To this date, this is the lowest value of $g^{(2)}(0)$ reported for any single--photon source even compared to the previously best background subtracted values. We achieve this result on GaAs/AlGaAs quantum dots embedded in a low--Q planar cavity by employing (i) a two--photon excitation process and (ii) a filtering and detection setup featuring two superconducting single--photon detectors with ultralow dark-count rates of $(0.0056\pm0.0007) s^{-1}$ and $(0.017\pm0.001) s^{-1}$, respectively. Re--excitation processes are dramatically suppressed by (i), while (ii) removes false coincidences resulting in a negligibly low noise floor.