Excess Noise Analysis of Continuous Variable Quantum Key Distribution

Excess noise will seriously affect the security of the quantum key in a reverse reconciliation coherent-state quantum key distribution system. Theoretical analysis of the excess noise in Alice's system, excess noise in channel and excess noise in Bob's homodyne detector are presented. And the bound of the excess noise in Alice, channel and Bob are also analyzed in the condition of ensuring the security of the quantum key. The results shows that the channel excess noise has the most serious impact to the security of the quantum key.