Fig. 10: Fidelity of satellite-to-ground entanglement transmission as a function of spectral irradiance.

We consider transmission of the Bell state Φ⁺ according to the scenario depicted in Fig. 8. The fidelity is given in eq. (29), and the average background photon number is given by \(\bar{n}={\mathcal{R}}\Delta T\), with \({\mathcal{R}}\) given by eq. (34). In order to calculate \({\mathcal{R}}\), we let λ = 810 nm, Δλ = 1 nm, Ω_fov = 100 μsr, r = 0.5 m, and ΔT = 1 ns; see, for e.g., refs ^70,99,110.