A coupled quantum dot laser amplifier using raman transitions between spin singlet and triplet states

We report the observation of Raman amplification in a three-level lambda scheme realized in a single coupled quantum dot (CQD) molecule. When both QDs contain a single electron, the lowest energy levels correspond to spin singlet (S) or triplet (T) states, which share a common optically excited state (X). Electron tunneling between the two dots gives rise to an exchange splitting between the S and T states, which allows us to selectively address them optically. We take advantage of fast (-10 ns) relaxation from T to S to generate population inversion and laser amplification on the T-to-X transition by pumping the S transition.