Overcoming power broadening of the quantum dot emission in a pure wurtzite nanowire

TL;DR

This paper demonstrates overcoming power broadening in quantum dot emission within ultraclean wurtzite nanowires, achieving high brightness and coherence at saturation, with implications for quantum network photon sources.

Contribution

It introduces a method to suppress power broadening in quantum dots using ultraclean nanowires, enhancing photon coherence at high emission rates.

Findings

Achieved single-photon count rates of 460,000 cps with >99% purity.

Extended coherence time to 1.2 ns at 300 mK, doubling previous values.

Reduced emission spectrum linewidth by increasing excitation power.

Abstract

One of the key challenges in developing quantum networks is to generate single photons with high brightness, purity, and long temporal coherence. Semiconductor quantum dots potentially satisfy these requirements; however, due to imperfections in the surrounding material, the coherence generally degrades with increasing excitation power yielding a broader emission spectrum. Here we overcome this power broadening regime and demonstrate the longest coherence at exciton saturation where the detection count rates are highest. We detect single-photon count rates of 460,000 counts per second under pulsed laser excitation while maintaining a single-photon purity of greater than 99%. Importantly, the enhanced coherence is attained with quantum dots in ultraclean wurtzite InP nanowires, where the surrounding charge traps are filled by exciting above the wurtzite InP nanowire bandgap. By raising the excitation intensity, the number of possible charge configurations in the quantum dot environment is reduced, resulting in a narrower emission spectrum. Via Monte Carlo simulations we explain the observed narrowing of the emission spectrum with increasing power. Cooling down the sample to 300 mK, we further enhance the single-photon coherence two-fold as compared to operation at 4.5 K, resulting in a homogeneous coherence time, T2, of 1.2 ns.