Fig. 2: Wavevector-resolved Bell-state measurement between write-out and read-out photons.
From: Massively-multiplexed generation of Bell-type entanglement using a quantum memory
a–d Coincidences between (sr, sw) = {(+, +), (+, −), (−, +), (−, −)} ports, respectively, with a single pair of Alice and Bob bases \(\{{\xi }_{{\rm{w}}}^{(2)},{\xi }_{{\rm{r}}}^{(2)}\}\). e–h Expected values of a measurement for subsequent combinations of \(\{{\xi }_{{\rm{w}}}^{(1)},{\xi }_{{\rm{w}}}^{(2)}\}\) and \(\{{\xi }_{{\rm{r}}}^{(1)},{\xi }_{{\rm{r}}}^{(2)}\}\) bases. Each expected value is a linear combination of coincidences between ± ports. i Bell parameter \({\mathcal{S}}({x}_{{\rm{s}}},{y}_{{\rm{s}}})\) retrieved by fitting a sine function (with xs and ys spatial frequencies) to the expected value for each combination of bases and taking the Bell linear combination of the results. j Bell parameter averaged over xs (red curve) along fitted sine (blue dashed curve) with amplitude 2.60 ± 0.19 indicating CHSH violation by more than three standard deviations σ. Subsequent shadings correspond to σ and 2σ. Solid lines indicate CHSH inequality violation threshold.
