Single Quantum Emitters in Monolayer Semiconductors

TL;DR

This paper introduces a new class of single quantum emitters in monolayer tungsten-diselenide, demonstrating their potential for scalable quantum photonic applications with narrow linewidths and strong photon anti-bunching.

Contribution

It reports the discovery and characterization of defect-localized exciton-based SQEs in 2D materials, a novel class differing from traditional 3D solid-state sources.

Findings

Narrow emission linewidths (~0.13 meV) significantly smaller than delocalized excitons.

Strong photon anti-bunching confirms single-photon emission.

Distinct fine structure with two polarized excitonic modes and a large exchange coupling.

Abstract

Single quantum emitters (SQEs) are at the heart of quantum optics and photonic quantum information technologies. To date, all demonstrated solid-state single-photon sources are confined in three-dimensional materials. Here, we report a new class of SQEs based on excitons that are spatially localized by defects in two-dimensional tungsten-diselenide monolayers. The optical emission from these SQEs shows narrow linewidths of ~0.13 meV, about two orders of magnitude smaller than that of delocalized valley excitons. Second-order correlation measurements reveal strong photon anti-bunching, unambiguously establishing the single photon nature of the emission. The SQE emission shows two non-degenerate transitions, which are cross-linearly polarized. We assign this fine structure to two excitonic eigen-modes whose degeneracy is lifted by a large ~0.71 meV coupling, likely due to the electron-hole exchange interaction in presence of anisotropy. Magneto-optical measurements also reveal an exciton g-factor of ~8.7, several times larger than that of delocalized valley excitons. In addition to their fundamental importance, establishing new SQEs in 2D quantum materials could give rise to practical advantages in quantum information processing, such as efficient photon extraction and high integratability and scalability.