Abstract
Security proofs that incorporate physical constraints of realistic heterodyne detectors are presented, establishing a rigorous analysis of collective attacks in a continuous-variable quantum cryptography scheme.
Highlights
Quantum key distribution (QKD) is the art of exploiting quantum optics to distribute a secret key between distant authenticated users
In CV QKD, information is decoded by a coherent measurement of the quantum electromagnetic field, i.e., homodyne or heterodyne
Ideal homodyne and heterodyne detection, which are measurements of the quadratures of the field, possess a continuous symmetry that plays a central role in our theoretical understanding of CV QKD
Summary
Quantum key distribution (QKD) is the art of exploiting quantum optics to distribute a secret key between distant authenticated users. By encoding information into the quantum electromagnetic field, QKD enables provably secure communication through an insecure communication channel, a task known to be impossible in classical physics This contrasts with standard and postquantum cryptography, which are based on computational assumptions and do not guarantee long-term security. A variety of protocols exist that differ in how the quadratures encode this information [3–7] When it comes to decoding, all CV-QKD protocols exploit coherent measurements of the field, i.e., either homodyne or heterodyne detection [8]. Furrer et al have considered digitized homodyne for a protocol based on the distribution of entangled states [6] and Matsuura et al have considered a binary encoding using coherent states, homodyne detection, and a test phase exploiting heterodyne [7] In both cases the key rates do not converge to the asymptotic bounds obtained in Refs. Collective attacks are not the most general attacks, they are known to be optimal, up to some finite-size corrections, through de Finetti reduction [13,21,22] While we focus on heterodyne detection, the same approach may be applied, with some modifications, to homodyne detection
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