Spin-flip Raman emission from a quantum dot molecule

InAs quantum dots (QDs) combine bright, high-purity single photon emission with a ground state spin qubit, providing an excellent solid state system for quantum information technologies. A quantum dot molecule, which consists of two neighboring QDs separated by a narrow tunnel barrier, has additional advantages. When each QD is charged with a single electron, a spin singlet-triplet Λ system is formed that can have a longer spin dephasing time than a single spin. Furthermore, optically driving near one arm of the system results in spin-flip Raman emission. We demonstrate that through this process the frequency, bandwidth, and pulse shape of the single Raman photons is controlled. We also perform quantum correlation measurements, including the second order correlation function g⁽²⁾(t) and indistinguishability of these photons. The ability to control the photon wavepacket of Raman emission should enable tunable and indistinguishable solid state single photon sources as well as efficient photon transfer in a quantum network.