title: Practical limitation for continuous-variable quantum cryptography using coherent States.
abstract: In this Letter, first, we investigate the security of a continuous-variable quantum cryptographic scheme with a postselection process against individual beam splitting attack. It is shown that the scheme can be secure in the presence of the transmission loss owing to the postselection. Second, we provide a loss limit for continuous-variable quantum cryptography using coherent states taking into account excess Gaussian noise on quadrature distribution. Since the excess noise is reduced by the loss mechanism, a realistic intercept-resend attack which makes a Gaussian mixture of coherent states gives a loss limit in the presence of any excess Gaussian noise.
authors.affiliation: CREST Research Team for Photonic Quantum Information, Department of Physics, Gakushuin University, Mejiro 1-5-1, Toshima-ku, Tokyo 171-8588, Japan. namiki@qo.phys.gakushuin.ac.jp
authors.forename: Ryo
authors.initials: R
authors.lastname: Namiki
authors.forename: Takuya
authors.initials: T
authors.lastname: Hirano