Exchange interaction and tunneling induced transparency in coupled quantum dots

TL;DR

This paper studies how tunneling and exchange interactions in coupled quantum dots can be controlled with electric fields and light polarization to produce transparency effects in their optical spectra, revealing insights into spin-preserving and spin-flip tunneling.

Contribution

It introduces a detailed model of excitonic states in quantum dot molecules considering exchange interactions and tunneling, demonstrating controllable tunneling-induced transparency in optical spectra.

Findings

Tunneling coupling creates a transparency window in absorption spectra.

External electric fields and polarization control enable manipulation of quantum interference.

Measurement of transparency window widths reveals tunneling amplitudes.

Abstract

We investigate the optical response of quantum dot molecules coherently driven by polarized laser light. Our description includes the splitting in excitonic levels caused by isotropic and anisotropic exchange interactions. We consider interdot transitions mediated by hole tunneling between states with the same total angular momentum and between bright and dark exciton states, as allowed by spin-flip hopping between the dots in the molecule. Using realistic experimental parameters we demonstrate that the excitonic states coupled by tunneling exhibit a rich and controllable optical response. We show that through the appropriate control of an external electric field and light polarization, the tunneling coupling establishes an efficient destructive quantum interference path that creates a transparency window in the absorption spectra, whenever states of appropriate symmetry are mixed by the carrier tunneling. We explore the relevant parameter space that allows probing this phenomenon in experiments. Controlled variation of applied field and laser detuning would allow the optical characterization of spin-preserving and spin-flip hopping amplitudes in such systems, by measuring the width of the tunneling-induced transparency windows.