Resonance fluorescence and laser spectroscopy of three-dimensionally confined excitons in monolayer WSe$_2$

TL;DR

This study demonstrates resonance fluorescence in monolayer WSe2, revealing single-photon emission, a weakly fluorescent exciton state, and providing insights into the quantum states of localized excitons in 2D semiconductors.

Contribution

It presents the first resonance fluorescence of three-dimensionally confined excitons in monolayer WSe2, enabling exploration of exciton coherence and valley-spin properties.

Findings

Achieved near-ideal single-photon fluorescence with up to 3 MHz count rate.

Identified a weakly-fluorescent exciton state ~5 meV blue-shifted from the ground state.

Performed high-resolution spectroscopy to understand quantum states of localized excitons.

Abstract

Resonant optical excitation of few-level quantum systems enables coherent quantum control, resonance fluorescence, and direct characterization of dephasing mechanisms. Experimental demonstrations have been achieved in a variety of atomic and solid-state systems. An alternative but intriguing quantum photonic platform is based on single layer transition metal chalcogenide semiconductors, which exhibit a direct band-gap with optically addressable exciton valley-pseudospins in a uniquely two-dimensional form. Here we perform resonance and near-resonance excitation of three-dimensionally confined excitons in monolayer WSe$_2$ to reveal near ideal single photon fluorescence with count rates up to 3 MHz and uncover a weakly-fluorescent exciton state ~ 5 meV blue-shifted from the ground-state exciton. We perform high-resolution photoluminescence excitation spectroscopy of the localized excitons, providing important information to unravel the precise nature of the quantum states. Successful demonstration of resonance fluorescence paves the way to probe the localized exciton coherence. Moreover, these results yield a route for investigations of the spin and valley coherence of confined excitons in two-dimensional semiconductors.