Keeping the photon in the dark

Quantum dots are excellent single photon sources, typically using the recombination of bright excitons (electron hole pairs). But quantum dots also host dark excitons, states that do not emit light and are therefore difficult to access.

In our latest work, we set out to address these dark states. Applying a magnetic field makes them slightly brighter through a spin flip, but they remain largely inaccessible. To overcome this, we use chirped laser pulses, which allow direct excitation into the dark state. Because dark excitons are long lived, the excitation can be stored before being retrieved with a second chirped pulse.

Combining our theoretical modeling with experiments from our colleagues, we demonstrate that this process indeed works.

This study was carried out in collaboration with the Photonics Group at the University of Innsbruck, the Semiconductor Division at JKU Linz, and Martin Axt's group at University of Bayreuth.

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