Controllable Photonic Time-Bin Qubits from a Quantum Dot

Photonic time-bin qubits are well suited to transmission via optical fibers and waveguide circuits. The states take the form 1/root(2)(alpha vertical bar 0 > + e(i phi) beta vertical bar 1 >) with vertical bar 0 > and vertical bar 1 > referring to the early and late time bin, respectively. By controlling the phase of a laser driving a spin-flip Raman transition in a single-holecharged InAs quantum dot, we demonstrate complete control over the phase, phi. We show that this photon generation process can be performed deterministically, with only a moderate loss in coherence. Finally, we encode different qubits in different energies of the Raman scattered light, paving the way for wavelengthdivision multiplexing at the single-photon level.