A coupled quantum dot laser amplifier: Raman transitions between spin singlet and triplet states

TL;DR

This paper demonstrates laser amplification via Raman transitions between entangled spin states in a quantum-dot molecule, paving the way for solid-state single-emitter lasers with unique quantum features.

Contribution

It reports the first observation of steady-state laser amplification in Raman transitions between spin states of a quantum-dot molecule, highlighting a new approach for solid-state quantum lasers.

Findings

Observation of laser amplification in Raman transitions

Electric-dipole coupling between spin states and excited state

Potential for continuous-wave single-emitter laser in solid state

Abstract

A holy grail of photonics research is the realization of a laser that uses a single quantum emitter as the gain medium. Such a device would exhibit a plethora of new features, including lasing without a well-defined threshold and output intensity fluctuations that remain below the shot-noise limit. While single-atom lasers have been demonstrated, compact devices capable of continuous-wave operation require monolithic structures involving a solid-state quantum emitter. Here, we report the observation of steady-state laser amplification in Raman transitions between the lowest-energy entangled spin states of a quantum-dot molecule. Absorption and resonance fluorescence experiments demonstrate that the singlet and triplet states have electric-dipole coupling to a common optically excited state. Fast spin relaxation ensures population inversion on the triplet transition when the singlet transition is driven resonantly. By embedding the quantum-dot molecule in a cavity of modest quality factor, a solid-state single-emitter laser could be realized.