Quantum key distribution with continuous variables

Abstract

We study a new quantum cryptography protocol with continuous variables for the construction of secret quantum keys. The protocol is based on pairs of Einstein-Podolsky-Rosen entangled quadratures of a two-mode electromagnetic field generated by non-degenerate parametric amplification. Instantaneous measurements of the quantum fluctuations provide the random bits of the secret key. The irreversible alteration of the quadrature entanglement due to unauthorized measurements immunizes the quantum key distribution against eavesdropping attacks. Based on two identical non-degenerate parametric amplifiers, the protocol circumvents the usual 50% bits rejection due to base incompatibility during the key generation process, and avoids the need for homodyne detection schemes which are highly sensitive to the mode matching problems.