Differential-Phase-Shift Quantum Key Distribution Quantum Key Distribution Kyo Inoue Osaka...

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.)

(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

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

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 !

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

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

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

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

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 %.

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

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.

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.

. . . .< 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

Quantum Relaying DPS-QKD

・・・・・・・・

Entanglementgeneration

Entanglementgeneration

signal 1 idler 1・・・・

signal 2・・・・

idler 2Alice Bob

Charlie

Experiment: Entanglement Transmission

DSF(50km)

frequencyup-conversiondetector

LD1551nm

IM EDFA FBG


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)



QE: 4.4 1.4 %d.c.: 4kcps

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)

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.

(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.

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

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

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

・・・・・・・・

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

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.

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.


att.

error correctionprivacy amplification final key rate: 1.5 kbps

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

Differential-Phase-Shift Quantum Key Distribution Quantum Key Distribution Kyo Inoue Osaka...

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