Continuous-variable quantum key distribution with a locally generated local oscillator

Transcription

1 Continuous-variable quantum key distribution with a locally generated local oscillator Bing Qi, Pavel Lougovski, Raphael Pooser, Warren Grice, Miljko Bobrek, Charles Ci Wen Lim, and Philip G. Evans Quantum information science group Oak Ridge National Laboratory Qcrypt 2016, Sept 12 16, 2016

2 Outline Continuous-variable (CV) QKD based on coherent detection Why *local* local oscillator ()? Our solution: theory & experiment Conclusion & outlook 2

3 Detection techniques in QKD Single photon detector (SPD) Widely applied in various QKD protocols; Performance improved over the years; Presently, high cost. Optical homodyne detection Build upon highly efficient photo-diodes working at room temperature cost effective; Immune to broadband background light QKD Weak signal Photo diode Diff. photo current through lit fiber 1,2 or free space 3 ; Require a reliable phase reference. Strong Beam splitter 3 B. Qi, et al., New J. Phys. 12, (2010) R. Kumar, et al., New J. Phys. 17, (2015) B. Heim, et al., New J. Phys. 16, (2014)

4 Gaussian-modulated coherent state (GMCS) QKD Protocol P A p A x A X A 1. Quantum state transmission X B X A P B P A x A + ip A 2. Classical Information Exchange Single-homodyne measure X or P 1 Double-homodyne measure X and P 2 Uncertainty Principle Gain information on X (P) introduce noise on P (X) 4 F. Grosshans, et al., Nature (2003) C. Weedbrook, et al., Phys. Rev. Lett. 93, (2004)

5 A gap between theory and practice Theory A crucial assumption trusted Security could be compromised if Eve can manipulate the Practice H. Häseler, et al., Phys. Rev. A 77, (2008) X.-C. Ma, et al., Phys. Rev. A 87, (2013) J.-Z. Huang, et al., Phys. Rev. A 87, (2013) P. Jouguet, et al., Phys. Rev. A 87, (2013) J.-Z. Huang, et al., Phys. Rev. A 89, (2014) The propagates through the insecure channel security issue > 10 8 photons/pulse vs. signal ~ 1 photon/pulse complicated system design Sig Laser PD 5 t Quantum channel t Sig

6 CV-QKD with *locally* generated Laser2 Challenge How to establish phase reference between independent lasers? Laser1 Quantum signal Photo diode Diff. photo current Solution Quadrature-remapping scheme Pilot-aided phase recovery 6

7 Quadrature-remapping scheme Scheme Measure in *random* basis Determine phase difference & rotate data in post-processing Slow phase drift: can be determined from quantum signals B. Qi, et al., Phys. Rev. A 76, (2007) Alice P A Fast phase change? P B X B X P B B X A X cos P A X A A sin P A sin cos 7

8 Pilot-aided phase recovery scheme Scheme Noise analysis R i S i R i+1 Phase noise Laser1 Laser2 IM IM T d t 0 t 1 T d t 2 Double Homodyne σ = Δθ S(T d ) 2 + Δθ L (T d ) 2 2 Δθ(T d ) 2 = 2T d τ c τ c laser coherence time + 2N 0 ηn ref Φ R,i Φ R,i+1 Excess noise Φ S,i = Φ R,i +Φ R,i+1 2 ε θ = V A σ 8 M. Koashi, Phys. Rev. Lett. 93, (2004) B. Qi, et al., Phys. Rev. X 5, (2015)

9 Determine laser phase noise Setup PC BD Results L BS 90 Optical hybrid OSC Delay T d Sig 90 shift 9 L Clarity-NLL-1542-HP (Wavelength Reference) BD 350MHz balanced photodetector (Thorlabs) Δθ(T d ) 2 = 2T d τ c Phase T d =20ns is 0.040±0.001 o High rate T d =100ps phase noise could be Khan, et al., Continuous-Variable Quantum Communication at 10 GHz and Compatible with Telecom Networks Poster sessions (Thursday) o Improved scheme A. Marie et al., arxiv: (2016)

10 Proof-of-principle experiment AM PM R i S i R i+1 20ns 20ns PC BD S Ch 1 Ch 2 AWG Sync to OSC 25km SMF L 90 Optical hybrid OSC 10

11 Classical BPSK Experimental results Reference photon number Measured phase noise: 0.040±0.001 Quantum input 11 Detector noise: 0.83 in shot-noise unit

12 Simulation results Asymptotic key rate against collective attack 1 Data size for composable security 2 Realistic model: Eve cannot control noise/loss in Bob. α=0.2db/km; ν el =0.1; =0.5; =0.04; f=0.95; V A =1 Fiber length=10km, ν el =0; other parameters are the same 12 S. Fossier, et al., J. Phys. B 42, (2009) A. Leverrier, Phys. Rev. Lett. 114, (2015)

13 Conclusion & outlook Conclusion: we proposed CV-QKD with local Remove potential security loopholes Simplify CV-QKD implementation Outlook: cost-effective QKD The gap between classical and quantum coherent communication systems is becoming smaller It is conceivable to conduct both classical communication and QKD using the same infrastructure 13 B. Qi, arxiv: v2(2016)

14 Related works Papers o B. Qi, et al., Phys. Rev. X 5, (2015) o D. B. S. Soh, et al., Phys. Rev. X 5, (2015) o D. Huang, et al., Opt. Lett. 40, 3695 (2015) o A. Marie et al., arxiv: (2016) Poster sessions o o o T. Iskhakov, et al., "Single Quadrature Continuous Variable Quantum Key Distribution with a Local Local Oscillator", Tuesday B. Schrenk, et al., "Pilot-Assisted Local Oscillator Synchronisation for CV-QKD", Thursday L. T. Vidarte, et al., "Proof-of-Principle Study of Self-Coherent Continuous-Variable Quantum Key Distribution", Thursday 14