Exciton-spin memory with a single semiconductor quantum dot molecule

We present an exciton-spin memory scheme using a single QDM consisting of two InAs QDs separated by a thin GaAs tunnelling barrier. Electrical control of the electron-hole spatial separation allowed the exciton lifetime to be tuned in the 1-1000 ns range. Storage and read-out operations were implemented using sub nanosecond modulation of the lifetime and photon storage up to 1μs was demonstrated. Using resonant excitation the circular polarisation of photons was transferred and stored in the exciton Zeeman states of a QDM under a magnetic field. The delayed emission was clearly co-polarised with the excitation light and a combined fidelity of 80% for the write and read operations was achieved.