Continuous Variable QKD Protocols in Realistic Environments and Entanglement Verification in Qubit-Mode Systems

摘要

Continuous variables techniques in quantum key distribution are characterized by the replacement of photon counting by homodyne or heterodyne detection. We investigate expected key rates using coherent states with a Gaussian distribution of amplitudes as signal states and pay special attention to excess noise in the channel and to the fact that any practical error correction will deviate from the ideal Shannon limit. We propose a combination of reverse reconciliation and post-selection to provide stable key rates. We also analyse the situation of just two input states in a noiseless environment and limits of the tolerable excess noise.