Fig. 3: Generation and verification of Bell states.

a Experimental sequence consisting of the preparation of spin and photonic qubits, the entanglement protocol, and readout. The spin state is initialized and read out by optically driving the \(\left\vert \Uparrow \right\rangle \leftrightarrow \left\vert \uparrow \Downarrow \Uparrow \right\rangle\) transition (pale red) and \({\hat{R}}_{i}\) controls the spin projection basis. The photonic qubit is prepared and measured by the same interferometer in either the Z-basis (green) or equatorial basis (blue) time window. b Raw two-photon coincidences measured during the photonic (p) readout window and spin (s) projections. c Measured two-photon coincidences corrected for laser background. d Visibility fringes of background-corrected two-photon coincidences as a function of the qubit phase θ_p when the spin state is projected on \({\left\vert -X\right\rangle }_{s}\propto \left\vert \Uparrow \right\rangle -\left\vert \Downarrow \right\rangle\). Circles (squares/triangles) correspond to projection on the photonic X-basis (±Z-basis). Solid curves are fits using \({V}_{s}\cos ({\theta }_{p}+{\theta }_{{{{\rm{offset}}}}})\), and dashed lines are horizontal line fits.