Table 1.

Measurement results

Swapped state03+03
VH/V0.618 ± 0.0670.610 ± 0.062
VP/M0.607 ± 0.0600.556 ± 0.065
VR/L0.624 ± 0.0560.542 ± 0.065
V¯0.616 ± 0.0350.569 ± 0.037
W = 1/2 − (1 + 3V¯)/4−0.212 ± 0.027−0.177 ± 0.028
Local S value2.487 ± 0.2872.469 ± 0.287
  • Numerical values of the measurement results including the individual visibilities VH/M, VP/M, and VR/L in the three mutually unbiased bases horizontal/vertical (H/V), plus/minus (P/M), and right/left (R/L) as well as the mean visibility V, the expectation value of the entanglement-witness operator W, and the locally measured S value. Over the 143-km free-space link the entanglement witness was more than 6 SDs beyond the classical bound of 0. This proved the presence of entanglement between photons “0” and “3” in the states ∣Ψ03 and ∣Ψ+03. The violation of a CHSH-type Bell inequality was shown locally on La Palma, underlining the quality of our setup. All outcomes are given for the swapped states ∣Ψ03 and ∣Ψ+03 with the respective SDs assuming Poissonian photon statistics.