Fig. 2: Coherent single-photon scattering and spin control.

a Setup for measuring photon visibility. The time-bin encoded qubit is reflected off the QD, which is initialized in the \(\left\vert \Uparrow \right\rangle\) state. Upon entering the interferometer, the early time-bin is delayed, which interferes with the late time-bin, constituting a \({\left\vert \pm X\right\rangle }_{p}=\left\vert e\right\rangle \pm \left\vert l\right\rangle\) basis measurement. PBS, polarizing beam-splitter; BS, 50:50 beam-splitter; QWP (HWP), quarter (half) wave-plate. b Intensity visibility in photonic X-bases as a function of the mean photon number per pulse \(\bar{n}\). The pure dephasing rate γ_d is extracted from the y-intercept where \(\bar{n}=0\). c The spin-echo sequence used to probe the spin coherence. The π-pulse is equally distant from the two π/2 pulses to eliminate inhomogeneous spin dephasing. The phase of the last π/2 pulse ϕ_r maps the equatorial state \(\left\vert \Uparrow \right\rangle +{e}^{i{\phi }_{r}}\left\vert \Downarrow \right\rangle\) to the optically bright state \(\left\vert \Uparrow \right\rangle\) (ϕ_r = π) or dark state \(\left\vert \Downarrow \right\rangle\) (ϕ_r = 0). d Contrast between the spin \(\left\vert \Downarrow \right\rangle\) and \(\left\vert \Uparrow \right\rangle\) populations as a function of ϕ_r.