Channel Parameters
Noise Sources
Modulation
11.5
Channel Noise χ_line
11.8
Total Noise χ_tot
2.5%
Excess Noise %
-8.5
SNR (dB)
Noise vs Distance
Key Rate Sensitivity to Excess Noise
Noise Budget Breakdown
Shot Noise Units (SNU)
In CV-QKD, noise is measured relative to the shot noise unit (SNU), which represents the quantum vacuum noise variance.
• Shot noise = 1 SNU (by definition)
• Excess noise ξ typically ranges from 0.001 to 0.05 SNU
• Electronic noise should be < 0.01 SNU for good performance
• Channel-added noise χ_line = (1-T)/T grows exponentially with distance