Fig. 4: Characterization of entanglement in orthogonal bases. | npj Quantum Information

Fig. 4: Characterization of entanglement in orthogonal bases.

From: Scalable spin–photon entanglement by time-to-polarization conversion

Fig. 4

a Measured correlations in the σz σz basis. In the passive TPC scheme, photons which are generated in the first (second) excitation cycle and take the short (long) path enable direct projection in the \(\left|0/{-1}\right\rangle\) and \(\left|H/V\right\rangle\) (see methods). These photons enable the reconstruction of the diagonal density matrix elements of the spin-photon system. b Measured correlations in the σx σx basis. Photons which arrive at the path-erasing time slot are expected to reveal a polarization correlation with the spin state in the equatorial bases. We plot the conditional probability of measuring the electron spin in the \(\left|\pm{x}\right\rangle\) basis, upon detection of a ZPL photon, for a given interferometer phase ϕ, which sets the photon measurement basis to \(\left|\phi \right\rangle =(\left|H\right\rangle +{e}^{i\phi }\left|V\right\rangle )/\sqrt{2}\). The blue (orange) points show the measurement data for preparation of the entangled states \(\left|\psi \right\rangle =(\left|0\right\rangle \left|V\right\rangle \pm {e}^{i\phi }\left|-1\right\rangle \left|H\right\rangle )\sqrt{2}\), with corresponding sinusoidal fits (lines). The clear deviation from a flat line witnesses the entanglement generation. The phase uncertainty for each data point is ±0.18 radians, as determined from the resolution of the phase readout (see Supplementary Information). The error bars indicate the standard error of the mean.

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