Milestones in CV-‐QKD (cont’d) §� (2003) Reverse reconciliation introduced to overcome 3 dB loss limit [9] ú� In a reverse reconciliation protocol, Alice corrects her keys to have the same values as Bob’s §� (2004) No switching protocol was introduced to eliminate the need to change basis during encoding [10] ú� Simplifies implementation and enables higher secret key rates §� (2009-‐2011) CV-‐QKD proved secure [11, 12, 13] [1] T. C. Ralph, “Continuous variable quantum cryptography,” Phys. Rev. A, 61(1):010303, (1999). [2] T. C. Ralph, “Security of continuous-‐variable quantum cryptography,” Phys. Rev. A, 62, 062306 (2000). [3] M. Hillery, “<strong>Quantum</strong> cryptography with squeezed states,” Phys. Rev. A, 61(2):022309, Jan (2000). [4] M.D. Reid, “<strong>Quantum</strong> cryptography with a predetermined key, using continuous variable Einstein-‐Podolsky-‐Rosen correlations,” Phys. Rev. A, 62:022309, (2000). [5] D. Gottesman and J. Preskill, “Secure quantum key distribution using squeezed states,” Phys. Rev. A, 63:022309, (2001). [6] N.J. Cerf, M. Levy, & G. Van Assche, “<strong>Quantum</strong> distribution of Gaussian keys using squeezed states,” Phys. Rev. A, 63:052311,(2001). [7] F. Grosshans & P. Grangier, “Continuous variable quantum cryptography using coherent states,” Phys. Rev. Lett., 88:057902, (2002). [8] Ch. Silberhorn, T. C. Ralph, N. Lutkenhaus, and G. Leuchs, “Continuous variable quantum cryptography: Beating the 3 dB loss limit,” Phys. Rev. Lett., 89(16):167901, Sep (2002). [9] F. Grosshans, N. J. Cerf, J. Wenger, R. Tualle-‐Brouri, and P. Grangier, “Virtual entanglement and reconciliation protocols for quantum cryptography with continuous variables,” <strong>Quantum</strong> Information and Computation, 3:535–552, (2003). [10] C. Weedbrook, A. M. Lance, W. P. Bowen, T. Symul, T. C. Ralph, & P. K. Lam, “<strong>Quantum</strong> Cryptography without Switching,” Phys. Rev. Lett. 93, 170504 (2004). [11] R. Renner and J. I. Cirac, “de Finetti Representation Theorem for Infinite-‐Dimensional <strong>Quantum</strong> Systems and Applications to <strong>Quantum</strong> Cryptography,” Phys. Rev. Lett. 102 110504 (2009). [12] A. Leverrier and P. Grangier, “Unconditional Security Proof of Long-‐Distance Continuous-‐Variable <strong>Quantum</strong> Key Distribution with Discrete Modulation,” Phys. Rev. Lett. 102, 180504 (2009). [13] A. Leverrier and P. Grangier, “Erratum: Unconditional Security Proof of Long-‐Distance Continuous-‐Variable <strong>Quantum</strong> Key Distribution with Discrete Modulation [Phys. Rev. Lett. 102, 180504 (2009)],” Phys. Rev. Lett. 106, 259902(E) (2011).
CV-‐QKD in Free-‐Space Communications §� CV-‐QKD has several attractive features for optical communications in free space ú� Robust to background light � Homodyne detectors rely on a local oscillator laser co-‐ propagating with signal laser. Only photons with same frequency and same spatial mode as the local oscillator are detected ú� Robust to timing jitter � Local oscillator provide automatic timing reference ú� Robust to spatial jitter � As local oscillator and signal laser co-‐propagate in same spatial mode they both jitter spatially identically ú� No need for a “guide” laser � Adaptive optics can correct wavefront distortions due to propagation through atmosphere without need for a separate guide laser ú� Easily miniaturized opto-‐electronics
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