Direct Observation of Controlled Coupling in an Individual Quantum Dot Molecule

TL;DR

This paper demonstrates direct observation and control of quantum coupling in individual quantum dot molecules using electric fields, revealing anti-crossings and molecular character transitions.

Contribution

It provides the first direct experimental evidence of quantum coupling in single quantum dot molecules and explores its manipulation via electric fields.

Findings

Observation of anti-crossing between excitonic states.

Identification of direct and indirect exciton character.

Dependence of coupling strength on inter-dot separation.

Abstract

We report the direct observation of quantum coupling in individual quantum dot molecules and its manipulation using static electric fields. A pronounced anti-crossing of different excitonic transitions is observed as the electric field is tuned. Comparison of our experimental results with theory shows that the observed anti-crossing occurs between excitons with predominant spatially \emph{direct} and \emph{indirect} character. The electron component of the exciton wavefunction is shown to have molecular character at the anti-crossing and the quantum coupling strength is deduced optically. In addition, we determine the dependence of the coupling strength on the inter-dot separation and identify a field driven transition of the nature of the molecular ground state.