Table 1 Reference system parameters.

Parameter description	Value
Transmitter aperture diameter, T_X	8 cm
Receiver aperture diameter, R_X	70 cm
Gaussian Beam waist, w₀	4 cm
Source wavelength, λ	785 nm
Source rate, f_s	500 MHz
Satellite orbit altitude, h	500 km
Minimum elevation limit, \({\theta }_{\min }\)	10^∘
Intrinsic quantum bit error rate, QBER_I	0.5%
Extraneous count probability, p_ec	5 × 10⁻⁷
After-pulsing probability, p_ap	0.1%
System loss metric, \({\eta }_{{{{{{{{\rm{loss}}}}}}}}}^{{{{{{{{\rm{sys}}}}}}}}}\)	40 dB
↪ Diffraction loss at zenith, η_diff(λ, 90)	19.4 dB
↪ Atmospheric loss at zenith, η_atm(λ, 90)	0.6 dB
\(\left.\begin{array}{l}\!\!\!\!\!\!\!\!\!\!\!\!\!\!\!\!\!\!\!\!\!\!\hookrightarrow {{{{{{{\rm{Optical}}}}}}}}\,{{{{{{{\rm{inefficiency}}}}}}}}\\ \hookrightarrow {{{{{{{\rm{Imperfect}}}}}}}}\,{{{{{{{\rm{beam}}}}}}}}\,{{{{{{{\rm{propagation}}}}}}}}\end{array}\right\}{\eta }_{{{{{{{{\rm{int}}}}}}}}}\)	12.0 dB 8.0 dB
Correctness parameter, ϵ_c	10⁻¹⁵
Security parameter, ϵ_s	10⁻¹⁰

Transmitter, receiver, and source properties determine range and elevation-dependent loss. The system loss metric, \({\eta }_{{{{{{{{\rm{loss}}}}}}}}}^{{{{{{{{\rm{sys}}}}}}}}}\), defined as the link efficiency at zenith, is 40 dB. The ‘intrinsic’ system loss is broken down into two components (see the section ‘Loss modelling’). \({\eta }_{{{{{{{{\rm{loss}}}}}}}}}^{{{{{{{{\rm{sys}}}}}}}}}\) can be scaled to model other SatQKD systems that differ by a fixed link loss ratio, e.g. different T_X or R_X apertures, or detector efficiencies. The intrinsic quantum bit error rate, QBER_I, incorporates errors from source quality, receiver measurement fidelity, basis misalignment, and polarisation fluctuations, while the extraneous count probability, p_ec, incorporates detector dark count and background rate. The correctness and security parameters are used to determine the finite-block composable SKL.

Quick links

Search