Differential-Phase-Shift Quantum Key Distribution Quantum Key Distribution Kyo Inoue Osaka...
Transcript of Differential-Phase-Shift Quantum Key Distribution Quantum Key Distribution Kyo Inoue Osaka...
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Differential-Phase-Shift Quantum Key Distribution
Kyo InoueOsaka UniversityNTT Basic Research LaboratoriesJST CREST
Collaboration with
H. Takesue, T. Honjo (NTT Basic Res. Labs.)
Yamamoto group (Stanford Univ.)
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(1)DPS-QKDSetup & ProtocolEavesdroppingExperiments
(2) Modified protocol with decoy pulses
(3) Entanglement-based schemes
(4) DPS-QKD using macroscopic coherent light
(5) DPS quantum secret sharing
Contents
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T
. . . .att.
0.1-0.2 photon/pulseAlice
{0, π}
DET-1
DET-2
Bob
coherentpulsesource
phasemod.
T
DPS (Differential-Phase-Shift) QKD
. . . .. . . .
Δθ
= 0 DET-1
Δθ
= π DET-2
time
Protocol(1) Signal transmission(2) Bob Alice: photon detection time(3) Alice knows which detector clicked at Bob.(4) Key bits are created as
DET-1 = “0” DET-2 = “1”
Features・Simple configuration・Efficient usage of the time domain・No photon discarded・Robustness against photon number splitting attack
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Alice
Eve. .. .Bob
error
Eavesdropping - intercept & resend -
Tran
smitt
er
0.1-0.2 photon/pls.
・A photon is detected once in 10 slots.
・She sends a photon over two pulses with measured phase difference.
・She sends nothing for unmeasured slots.
41
21
21
=×
Eavesdropping !
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Eavesdropping - photon number splitting -
Bob
Eve
×
Alice
. .. .photon number measurement(QND)
split gatelossless
errorEavesdropping !
transmission loss (dB)
key
crea
tion
rate
(log
)
DPS
BB84 with laser
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DPS-QKD Experiment
cw-laser intensitymod.
phasemod.
att.
pulsepatterngenerator
rep. rate:10 GHz
{0, π}
datagenerator
. . . .
timeintervalanalyzer
fiber
logicunit
waveguideinterferometer
SSPDlow noisenon-gatinglow jitter
Takesue et al., Nature Photon., 1, 343 (2007)collaborating with NIST
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17 kbit/s at 100 km.12 bit/s at 200 km.
Secure key against general individual attackbased on Edo, Takesue, Yamamoto, PRA 73, 012344 (2006).
Result
QE=1.4 %d.c.=50 cps
SSPD
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Field Transmission
NTT Yokosuka R&D Center
NTTYokosuka Office
17.8 km
PPLNphoton (1.55μm)
pump (0.98μm)
0.6μm
Si-APDfilter
delay (200ps)
PBSBS
Up-conversion photon detector
for polarization independency
pulse rate: 1 GHz
λ/2
QE: 2 %, d.c.: 2.8 kcps
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0 100 200 3002
3
4
5
6
50000
100000
150000
QB
ER
(%
)
Time (min)
Sifted key generation rate (bps)
QBER 3.14% (Avr)
Rate 120.26kbps (Avr)
Result
Sifted key:120 kbit/s with a QBER of 3.14 %.
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(1)DPS-QKDSetup & ProtocolEavesdroppingExperiments
(2) Modified protocol with decoy pulses
(3) Entanglement-based schemes
(4) DPS-QKD using macroscopic coherent light
(5) DPS quantum secret sharing
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DPS-QKD with Decoy Pulses
. . . .
Bob
modified version
Eavesdropping is found by bit error rate
Alice BobEve bit erroreavesdropping !
Conventionally
Eve gets some key bits, utilizing system errors.
Alice
μ μ
10μ μ μ
. . . .
. . . .
μ 5.5μ
5.5μ μ
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Bob
Eve
Trans.
Intercept & Resend attack is prohibited.
decoy click
Intercept & Resend against DPS-QKD with Decoy
Eavesdropping !
. . . .
. . . .
. . . .
Alice
1 : 2 : 1count rate:
Eve does not know whether a click is decoy or not.
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distance (km)
key
crea
tion
rate
(/pu
lse)
Simulation
0 20 40 60 80 100 120
10-1
10-2
10-3
10-4
10-5
10-6
10-7
decoy DPS
conventional DPS suffering from general individual attack
fiber loss: 0.25 dB/kmdark count: 10-5/gatedetection efficiency: 0.120% fluctuates in detection rate.
Transmission length can be extended.
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(1)DPS-QKDSetup & ProtocolEavesdroppingExperiments
(2) Modified protocol with decoy pulses
(3) Entanglement-based schemes
(4) DPS-QKD using macroscopic coherent light
(5) DPS quantum secret sharing
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. . . .< 1 photon/pls.
BobAlice
signal idler
pumppulse source
・ ・・ ・
< 1 photon/pls.
DPS-QKD utilizing Entanglement
. . . .
. . . .
. . . .. . . .
. . . .
parametricmedium
correlation
secret key
Entanglement generation
future scheme for long distance
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Quantum Relaying DPS-QKD
・・ ・・ ・・ ・・
Entanglementgeneration
Entanglementgeneration
signal 1 idler 1・・ ・・
signal 2・・ ・・
idler 2Alice Bob
Charlie
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Experiment: Entanglement Transmission
DSF(50km)
frequencyup-conversiondetector
LD1551nm
IM EDFA FBG
waveguideinterferometer
Frequencyup-conversiondetector
1 GHz 100 ps
PPLN (SHG)
Filter
1.5μmsuppression
PPLN(parametric down conversion)
Filter
Filter
1555nm1547nm
pump (0.7-μm)Suppression
1547,1555nmseparation
DSF(50km)
waveguideinterferometer
timeintervalanalyzer
QE: 4.4 1.4 %d.c.: 4kcps
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24.0 24.50
5e−05
0.0001
0
5000
10000
15000
PLC temperature for idler (deg.)
Coi
ncid
ence
rat
e pe
r si
gnal
cou
nt
Count rate for idler (H
z)
Visibility of 81.6% without removing background noise.
Average number of photon pair: 0.07/pilse.
Time-bin entangled photons are successfully transmitted over 50 x 2 km.
Result
two-photon interference data on TIA
waveguide temperature for idler (deg)
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(1)DPS-QKDSetup & ProtocolEavesdroppingExperiments
(2) Modified protocol with decoy pulses
(3) Entanglement-based schemes
(4) DPS-QKD using macroscopic coherent light
(5) DPS quantum secret sharing
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BobAlice
{-δ, δ}dec.
δ Re[E]
Im[E]
θ4
θ3
θ2
θ1
θi = {δ, –δ}
θ4
θ3
θ2
θ1
θ4
θ3
θ2
θ1
Coherentsource
Δθ
= {δ, 0, –δ}
Phasemod.
DPS-QKD using Macroscopic Coherent Light
quantum noise
signal level, I
Prob
abili
ty
Conventionally, photon counting is needed.
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(1) Alice → Bob:Signal transmission
Secret key
Protocol
(2) Bob creates bit “1” when I > Id
bit “0” when I < - Id
(3) Bob → Alice:Time slot at which bit was created
(4) Alice creates bit “1” in case θi – θi+1 = 2δbit “0” in case θi – θi+1 = – 2δ
for the time slot at which Bob created bit.
(5) Alice → Bob:Time slots for which θi – θi+1 = 0
(6) Bob discards the bits for θi – θi+1 = 0
“0” “1”
Id-Id
Conventional photodetectors are available.
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Fiber length (km)
Key
cre
atio
n ra
te (/
slot
)
BE
EBk
ββ
αα
≡
α:detection efficiency
β:noise factor
k is a parameter indicating performance of Bob’s detectorrelative to Eve’s.
Simulation (1)
0 10 20 30 40 50
1
10-1
10-2
10-3
10-4
10-5
k = 1
k = 0.5
k = 0.25
Final key creation rate: Rs (IAB – max{IAE , IBE })
Rs : sifted key rateIAB : mutual information between Alice & BobIAE : mutual information between Alice & EveIBE : mutual information between Bob & Eve
Alice
error correction
Bob
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Simulation (2)
0 50 100 150 200
fiber length (km)
1
10-1
10-2
10-3
10-4
10-5
key
crea
tion
rate
(/sl
ot)
k = 1
k = 0.5
k = 0.25
Final key creation rate: Rs (IAB – IBE )
Alice
error correction
Bob
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(1)DPS-QKDSetup & ProtocolEavesdroppingExperiments
(2) Modified protocol with decoy pulses
(3) Entanglement-based schemes
(4) DPS-QKD using macroscopic coherent light
(5) DPS quantum secret sharing
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Quantum Secret Sharing (QSS)Function
Alice and Bob have fractions of a secret key shared with Charlie.Alice (or Bob) cannot decipher message from Charlie by her (or him) alone.
Previous scheme
Alicesecrete key
partial key partial key
secrete key Bob
Charlie
- Entanglement based scheme- BB84 based scheme
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・ ・・ ・ ・ ・・ ・
phasemod.{0, π}
coherentpulsesource
phasemod.
monitor
~ 1ph./plsatt.
Alice CharlieBob
ΔθaΔθb “0”
“1”
0 π0 “0” “1”π
“1” “0”
Δθa
Δθb
{0, π}
DPS Quantum Secret Sharing (QSS)
Charlie’s data are XOR of Alice’s and Bob’s.
・ ・・ ・
・ ・・ ・
Charlie’s data are recovered in collaboration of Alice and Bob. QSS
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Eavesdropping by dishonest Bob
Eavesdropping by dishonest Alice
phasemod. Charlie
Bob
coherentpulsesource
Bob cannot fully know Alice’s data.
measure
phase mod. Charlie
Bob Alice
Alice
Eavesdropping against DPS-QSS
Alice ~ 0.1 photon/pls.
~ 0.1 photon/pls. coherentpulsesource
measurephasemod.
Alice cannot fully know Bob’s data.
Bob’s monitoring forces Alice to send 0.1 ph/pls.
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fiber(5km)
fiber(5km)
rep: 1 GHzpulse width: 125 ps
0.1 ph./pls
waveguide interferometer
ΔL = 20 cm
1 Gbps 1 Gbps
10:1 coupler
APD
APD(4MHz)
QBER: 6.4 %sifted key rate: 3.9 kbps
Experiment
cw-laser intensitymod.
pulsepatterngenerator
datagenerator
phasemod.
datagenerator
phasemod.
timeintervalanalyzer
att.
error correctionprivacy amplification final key rate: 1.5 kbps
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Summary
(3) Entanglement-based schemesExperiment utilizing fiber four-wave mixing for entanglement generation.
DPS-QKD is presented.
(1) Setup & protocol, eavesdropping, experimentsSimple configuration, no photon discarded.Robust against photon-number-splitting attack12 bit/s at 200 km, 17 kbit/s at 100 km for secure key (with SSPD)
(2) Modified protocol with decoy slotsIntercept-resend attack is prohibited.
(4) DPS-QKD using macroscopic coherent lightConventional photodetectors are available.
(5) DPS quantum secret sharingSimple configuration