Spin-resolved quantum-dot resonance fluorescence

Confined spins in self-assembled semiconductor quantum dots promise to serve both as probes for studying mesoscopic physics in the solid state and as stationary qubits for quantum-information science(1-7). Moreover, the excitations of self-assembled quantum dots can interact with near-infrared photons, providing an interface between stationary and 'flying' qubits. Here, we report the observation of spin-selective photon emission from a resonantly driven quantum-dot transition. The Mollow triplet(8) in the scattered photon spectrum-the hallmark of resonance fluorescence when an optical transition is driven resonantly-is presented as a natural way to spectrally isolate the photons of interest from the original driving field. We also demonstrate that the relative frequencies of the two spin-tagged photon states can be tuned independent of an applied magnetic field through the spin-selective dynamic Stark effect, induced by the same driving laser. This demonstration should be a step towards the realization of challenging tasks such as electron-spin readout, heralded single-photon generation for linear-optics quantum computing and spin-photon entanglement.