Quantum cryptography approaching the classical limit.

We consider the security of continuous-variable quantum cryptography as we approach the classical limit, i.e., when the unknown preparation noise at the sender's station becomes significantly noisy or thermal (even by as much as 10(4) times greater than the variance of the vacuum mode). We show that, provided the channel transmission losses do not exceed 50%, the security of quantum cryptography is not dependent on the channel transmission, and is therefore incredibly robust against significant amounts of excess preparation noise. We extend these results to consider for the first time quantum cryptography at wavelengths considerably longer than optical and find that regions of security still exist all the way down to the microwave.

[1]  Nicolas J. Cerf,et al.  Virtual entanglement and reconciliation protocols for quantum cryptography with continuous variables , 2003, Quantum Inf. Comput..

[2]  Miguel Navascués,et al.  Optimality of Gaussian attacks in continuous-variable quantum cryptography. , 2006, Physical review letters.

[3]  Nicolas Cerf,et al.  From quantum cloning to quantum key distribution with continuous variables: a review (Invited) , 2007 .

[4]  S. Lloyd,et al.  Characterization of collective Gaussian attacks and security of coherent-state quantum cryptography. , 2008, Physical review letters.

[5]  Christian Weedbrook,et al.  Quantum cryptography without switching. , 2004, Physical review letters.

[6]  Marcella Giovannini,et al.  Mid-infrared single-photon counting. , 2006, Optics letters.

[7]  J. Cirac,et al.  De Finetti representation theorem for infinite-dimensional quantum systems and applications to quantum cryptography. , 2008, Physical review letters.

[8]  R. Rosenfeld.  Nature , 2009, Otolaryngology--head and neck surgery : official journal of American Academy of Otolaryngology-Head and Neck Surgery.

[9]  V. Scarani,et al.  The security of practical quantum key distribution , 2008, 0802.4155.

[10]  G Leuchs,et al.  Continuous variable quantum cryptography: beating the 3 dB loss limit. , 2002, Physical review letters.

[11]  C. E. SHANNON,et al.  A mathematical theory of communication , 1948, MOCO.

[12]  Thomas M. Cover,et al.  Elements of Information Theory , 2005 .

[13]  Thierry Paul,et al.  Quantum computation and quantum information , 2007, Mathematical Structures in Computer Science.

[14]  P. Grangier,et al.  Continuous variable quantum cryptography using coherent states. , 2001, Physical review letters.

[15]  N. Cerf,et al.  Unconditional optimality of Gaussian attacks against continuous-variable quantum key distribution. , 2006, Physical Review Letters.

[16]  P. Knight,et al.  Introductory quantum optics , 2004 .

[17]  N. Cerf,et al.  Quantum key distribution using gaussian-modulated coherent states , 2003, Nature.

[18]  Radim Filip.  Continuous-variable quantum key distribution with noisy coherent states , 2008 .

[19]  Anthony Leverrier,et al.  Unconditional security proof of long-distance continuous-variable quantum key distribution with discrete modulation. , 2008, Physical review letters.

[20]  Vikram Sharma,et al.  No-switching quantum key distribution using broadband modulated coherent light. , 2005, Physical review letters.

[21]  Seth Lloyd,et al.  Continuous Variable Quantum Cryptography using Two-Way Quantum Communication , 2006, ArXiv.

[22]  Vladyslav C. Usenko,et al.  Feasibility of continuous-variable quantum key distribution with noisy coherent states , 2009, 0904.1694.