LAUSR

Continuous variable quantum key distribution attracts increasing attention in recent years due to its potential high secret key rates and the compatibility with existing communication infrastructure. This letter derives the secret key rate for a binary modulated continuous variable quantum key distribution using an optimally displaced threshold detection and post-selection. To improve the secret key rate, we optimize the post selected area and the coherent amplitude for different transmission efficiency of the channel under different thermal noises. Both the individual and collective beamsplitter attacks are considered. Numerical results show that the secret key rate using the optimally displaced threshold detection can surpass that using the classical detection scheme under different transmission efficiencies and different thermal noises. Besides, more improvement on the secret key rate can be obtained when the transmission efficiency is low.