Photonic time-bin qubits are well suited to transmission via optical fibers and waveguide circuits. The states take the form 1 ffiffiffiffi ffi ð2Þ p ðαj0i þ e iϕ βj1iÞ, with j0i and j1i 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, 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 wavelengthdivision multiplexing at the single-photon level.

We exploit the nonlinearity arising from the spin-photon interaction in an InAs quantum dot to demonstrate phase shifts of scattered light pulses at the single-photon level. Photon phase shifts of close to 90 • are achieved using a charged quantum dot in a micropillar cavity. We also demonstrate a photon phase switch by using a spin-pumping mechanism through Raman transitions in an in-plane magnetic field. The experimental findings are supported by a theoretical model which explores the dynamics of the system. Our results demonstrate the potential of quantum dot-induced nonlinearities for quantum information processing. *