Upload
wtyru1989
View
237
Download
5
Tags:
Embed Size (px)
Citation preview
Why is QKD not used?Towards high-performance CVQKD
Practical security considerations
Experimental Demonstration ofContinuous-Variable Quantum Key Distribution
over 80 km of Standard Telecom Fiber
Paul Jouguet, Sebastien Kunz-Jacques, AnthonyLeverrier, Philippe Grangier, Eleni Diamanti
SeQureNet, Telecom ParisTech
2012-09-14
1/20
Why is QKD not used?Towards high-performance CVQKD
Practical security considerations
QKD: four main limitations (1/2)
Speed
I Not enough for OTP: not a serious issue
I Physical parameters estimation over large blocks: hardwaredrifts, latency
Distance
I Asymmetric crypto is not limited
I Trusted nodes are not a good solution: quantum repeaters arerequired
2/20
Why is QKD not used?Towards high-performance CVQKD
Practical security considerations
QKD: four main limitations (2/2)
Security
I Incomplete security proofs
I Distance between proofs and practical implementations
Deployment
I QKD requires a dark fiber: $$$
I WDM compatibility: lowers QKD extra premium
3/20
Why is QKD not used?Towards high-performance CVQKD
Practical security considerations
Two technologies
Discrete variables Continuous variables
medium photon phase/polar. field amplitude-phasedetection photon counters coherent detection
range 100 km 25kmrate 1Mb/s 10kb/s
components active cooling standardintegration WDM WDM
security yes yes
4/20
Why is QKD not used?Towards high-performance CVQKD
Practical security considerations
Gaussian protocol
Losses and excess noise lower the SNR.
5/20
Why is QKD not used?Towards high-performance CVQKD
Practical security considerations
Optical setup
6/20
Why is QKD not used?Towards high-performance CVQKD
Practical security considerations
Speed limitations
I Delay between classical and quantum signals (200ns)
I Laser pulsed with a tunable frequency (1MHz)
I Data acquisition speed (up to 5MHz)
I Filtering: tradeoff between speed and electronic noise (currentcutoff at 10MHz, 100MHz feasible arxiv:1006.1257 Yue-MengChi et al.)
I High-speed error correction: LDPC codes (GPU) or polarcodes (CPU) (up to 10Mbit/s) (arxiv:1204.5882, P. Jouguetand S. Kunz-Jacques)
7/20
Why is QKD not used?Towards high-performance CVQKD
Practical security considerations
Range limitations
I High error-correction efficiency, even at low SNRs
I Finite-size effects
I Low SNR Alice/Bob synchronization mechanism
I Low-loss LO path
I Excess noise (imperfect relative phase estimation)
New SNR regions allowed by error-correction techniques.
8/20
Why is QKD not used?Towards high-performance CVQKD
Practical security considerations
Channel virtualization
I Idea introduced by Leverrier (Phys. Rev. A 77, 042325(2008))
I Translates the initial problem into a channel coding problemon a good channel
I Good means very efficient error-correcting codes available
I Usual suspect: BIAWGNC
9/20
Why is QKD not used?Towards high-performance CVQKD
Practical security considerations
How to improve the efficiency of the multidimensionalscheme?
I Improve the approximation between the virtual channel andthe target channel
I Improve the efficiency of the codes on the target channel(Phys. Rev. A 84, 062317 (2011), P. Jouguet, S.Kunz-Jacques and A. Leverrier)
10/20
Why is QKD not used?Towards high-performance CVQKD
Practical security considerations
What is a good code for the BIAWGNC?
I A code is designed for a channel and a SNR
I Free parameter: the code rate R = n−mn , m the number of
parity-check equations, n the length
I Low SNR / Lot of redundancy / Low rate
I Efficiency β (SNR) = RC(SNR)
I Typical values:I Slice reconciliation: β = 90%, SNR= 3, @30kmI Multidimensional reconciliation: β = 89%, SNR= 0.5, @50km
11/20
Why is QKD not used?Towards high-performance CVQKD
Practical security considerations
Set of available codes
β SNR
93.6% 1.09793.1% 0.16195.8% 0.07596.9% 0.02996.6% 0.014595.9% 0.00725
12/20
Why is QKD not used?Towards high-performance CVQKD
Practical security considerations
How to get more flexibility on the SNR?
I Possible to design codes with lower rates
I Not necessary: repetition codes
I Shortening, puncturing
I Optimization on the modulation variance
13/20
Why is QKD not used?Towards high-performance CVQKD
Practical security considerations
Theoretical secret key rate
Parameters: VA ∈ {1, 100}, T = 10−0.2d/10, ξ = 0.01, η = 0.6,Velec = 0.01
10−6
10−5
0.0001
0.001
0.01
0.1
1
0 20 40 60 80 100 120 140 160 180
Key
rate
(secretbits/pulse)
Distance (km)
1SNR=1.097 (1)
2
SNR=0.161 (2)
3
SNR=0.075 (3)
4
SNR=0.029 (4)
5
SNR=0.0145 (5)
6
SNR=0.00725 (6)
14/20
Why is QKD not used?Towards high-performance CVQKD
Practical security considerations
Finite size effects
I First analysis for discrete modulation protocols in Phys. Rev.A 81, 062343 (2010), Leverrier et al.
I Statistical uncertainty over estimated parameters (T , ξ)
I K = nN (βI (x ; y)− SεPE (y ;E )−∆(n))
I Extended analysis for Gaussian modulation, includingimperfect homodyne detection (efficiency, electronic noise)and shot noise estimation (Phys. Rev. A 86, 032309 (2012),poster 33)
I Main effect: uncertainty on the excess noise ξ
15/20
Why is QKD not used?Towards high-performance CVQKD
Practical security considerations
Experimental results
Parameters: d = 53km, η = 0.552, Velec = 0.015, SNR= 0.17,β = 94%, ε = 10−10
-0.0005
0
0.0005
0.001
0.0015
0.002
0 5 10 15 20
Excess
noise(shotnoiseunits)
Time (hours)
excess noisestd dev of the experimental excess noise
std dev of the theoretical estimator (108 samples)std dev of the theoretical estimator (106 samples)
16/20
Why is QKD not used?Towards high-performance CVQKD
Practical security considerations
Experimental results
Parameters: d = 53km,80km, η = 0.552, Velec = 0.015,SNR=0.17,0.08, β = 94%, ε = 10−10
100
1000
10000
100000
0 20 40 60 80 100
Key
rate
(bit/s)
Distance (km)
asymptotic theoretical key rate�nite-size theoretical key rate (108 samples)
asymptotic experimental point�nite-size experimental point (108 samples)
17/20
Why is QKD not used?Towards high-performance CVQKD
Practical security considerations
Imperfect preparation
I Thermal noise (Phys. Rev. A 81, 022318 (2010), Usenko andFilip)
I Gaussian modulation: truncated and discretized (finiteamount of randomness)
I Can be taken into account into the security proof (Phys. Rev.A 86, 032309 (2012), poster 33)
I But a lot of random numbers are required (+ sifting andmultidimensional protocol)
I Calibration proceduresI Calibration of the homodyne detectionI Calibration of the phase noise
18/20
Why is QKD not used?Towards high-performance CVQKD
Practical security considerations
Summary
I Long distance CVQKD with Gaussian modulation is possiblethanks to low SNR error-correction capability
I Computing-power consuming because of decoding close to thethreshold
I We use GPU (30× faster than CPU plus friendly Moore’s law)
I Higher secure distance with virtual Gaussian post-selection?(arxiv:1205.6933, J. Fiurasek, N. J. Cerf, arxiv:1206.0936, N.Walk et al.)
I Work on WDM coming
19/20
Why is QKD not used?Towards high-performance CVQKD
Practical security considerations
Enquire about Cygnus
I An open and customizable CVQKD research platform
I Tests/demonstrations of integration in optical networks
20/20