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 √(2) (α|0⟩+eiϕβ|1⟩), with |0⟩ and |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-hole-charged InAs quantum dot, we demonstrate complete control over the phase, ϕ. 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 wavelength-division multiplexing at the single-photon level.