Electrical control of the exciton fine structure of a quantum dot molecule.

We electrically control the coherent mixing of the optically bright spin states of excitons confined in InAs/GaAs quantum dot molecules. By tunnel coupling two quantum dots, using a vertical electric field, the exciton fine structure splitting and eigenstate orientation relative to the crystal lattice are tuned. We model the electric field dependent anisotropic electron-hole exchange interaction accurately and propose that the controllable mixing of the spin states will enable electrically controlled quantum operations on exciton spin qubits.

Exciton-spin memory with a semiconductor quantum dot molecule.

We report on a single photon and spin storage device based on a semiconductor quantum dot molecule. Optically excited single electron-hole pairs are trapped within the molecule, and their recombination rate is electrically controlled over 3 orders of magnitude. Single photons are stored up to 1 µs and read out on a subnanosecond time scale. By using resonant excitation, the circular polarization of individual photons is transferred into the spin state of electron-hole pairs with a fidelity above 80%, which does not degrade for storage times up to the 12.5 ns repetition period of the experiment.