towards secure qkd with testable assump6ons on modula6on

Towards secure QKD with testable assump6ons on modula6on devices

AkihiroMizutani1Collaborators:YuichiNagamastu1,MarcosCurty2,Hoi-KwongLo3,KojiAzuma4,RikizoIkuta1,TakashiYamamoto1,NobuyukiImoto1,KiyoshiTamaki4

1OsakaUniversity2UniversityofVigo3UniversityofToronto4NTTBasicResearchLaboratories

PracHcalsecurityofQKD

Source

Measurement Bob

Alice

Eve

SecurityproofssofarmakeidealassumpHonsontheusers’devices.

Sourceimperfec,ons

RealisHcimperfecHons,evenmajorimperfecHonssuchasmodula,onerrors,arenottakenintoaccountinmostofsecurityproofs.

Measurement-device-independent(MDI)QKDH.K.Loetal,Phys.Rev.LeW.108,130503(2012).

L.Lydersenetal.,Nat.Photonics4,686(2010).Detectorblindinga:acks

Time-shi?a:acksY.Zhaoetal.,Phys.Rev.A78,042333(2008).

DetectorcontrolI.Gerhardtetal,Nat.Commun.2,349(2011).

Ø  Thesecurityofmostexis,ngimplementa,onsofQKDhasnotbeenrigorouslyestablishedyet.Why?

GLLPsecurityproofD.GoWesmanetal.,Quant.Inf.Comput.4,325(2004).Ø  Phase-encodingBB84

PhasemodulatorLaser Detector

OpHcalpulses

EvenunderthesmallphasemodulaHonerrors,theachievabledistanceandthekeyratedrasHcallydecrease.

BobAlice

GLLPanalysis Qubitspaceof2consecuHvepulses

:Idealstates:actualstates

Loss-tolerantprotocolØ  Loss-tolerantprotocol


OpHcalpulsesBobAlice

K.Tamakietal.,Phys.Rev.A90,052314(2014).

GLLPanalysis Loss-tolerantprotocol

Themainidea:UHlizingthe“basismismatchedevents”toesHmateEve’sleakedinformaHon.

Loss-tolerantprotocolØ  Loss-tolerantprotocol




TheLTprotocolassumesthatthephasemodulaHonerrorsfollowIID.

IIDdistribuHononmodulaHondevice

・・・

Loss-tolerantprotocol




Hardorevenimpossibletoconfirmintheexperiment.


Ø  Loss-tolerantprotocol





WeneedmorerelaxedassumpHonsonthesource.








TowardssecureQKDwithtestableassumpDonsonmodulaDondevices(seearXivsoon!)



WeneedmorerelaxedassumpHonsonthesource.


CharacterizaHonofmodulaHondevices

Phaseinterval Taggedpulses Failureprobability

AllthepulsesemiWedwithPhasemodulator:

•  Untaggedsignal:Pulsewhosephaseliesintheinterval•  Taggedsignal:Pulsewhosephasedoesnotlieintheinterval

Phasemodulator

Laser DetectorOpHcalpulses

Intensitymodulator




AllthepulsesemiWedwith

…Ø  Non-IIDmodulaHonerrorsareaccommodated.

Ø  IntervalsarepotenHallytestableinexperiments.

Phasemodulator:

Phasemodulator


Intensitymodulator



Intensitymodulator:


AllthepulsesemiWedwithPhasemodulator:

Intensityinterval Taggedpulses Failureprobability

AllthepulsesemiWedwith

Ø  Taggedeventsoccurindependentlyof

Phasemodulator


Intensitymodulator


Simula6on results

Finite-keylengthØ  Securekeylengthagainstcoherenta:acks:

NumberofZ-basisdetectedeventsfromuntaggedsingle-photonemissions

LeakedinformaHonfortheuntaggedsingle-photonemissions

BitsexchangedinreconciliaHon

Ø  Es,ma,onfortheparameters:

:Extendthe“decoy-statemethod”basedonourintensityintervalassumpHon.

M.Curtyetal.,Nat.Commun.,5,3732(2014).

:PhaseerrorratefortheuntaggedsinglephotonemissionsamongtheZ-basisuntaggedsingle-photonemissions.

seearXivsoon!

Keyrateagainstdistancen  Keyrate=keylengthpersignaltransmission.n  Secrecyparametern  Correctnessn  LossintheopHcalfiber=0.2dB/kmn  DetecHonefficiency=46%,darkcount= Y-L.Tangetal.,Phys.Rev.LeW.113,190501(2014).

F.Xuetal.,PRA92,032305(2015).

Modula,ondevicesPhaseinterval:

Intensityinterval(±3%):

=Probability(perpulse)ofbeingoutsidetheinterval

(5-sigma) (6-sigma)

Phasemodulator: Intensitymodulator:1.7°

0.03μ 0.03μ0 0.001

Keyrateagainstdistancen  Keyrate=keylengthpersignaltransmission.n  Secrecyparametern  Correctnessn  LossintheopHcalfiber=0.2dB/kmn  DetecHonefficiency=46%,darkcount= Y-L.Tangetal.,Phys.Rev.LeW.113,190501(2014).

NoHce1)  Ifincreases,thenumberofpulsesthatdonotliewithintheintervalsalsoincreases.ThetaggedsignalsbecomeproblemaHcespeciallyinthehighlossregime.2)  Iftheintervalsareguaranteedby5-sigmaconfidencelevel,morethan100kmsecureQKDispossiblewithinreasonablenumberofsignaltransmissions.

Modula,ondevicesF.Xuetal.,PRA92,032305(2015).Phaseinterval:



(5-sigma) (6-sigma)

Keyrateagainstdistance

(5-sigma) (6-sigma)

n  Keyrate=keylengthpersignaltransmission.n  Secrecyparametern  Correctnessn  LossintheopHcalfiber=0.2dB/kmn  DetecHonefficiency=46%,darkcount= Y-L.Tangetal.,Phys.Rev.LeW.113,190501(2014).


NoHceEvenifweassume±5%intensityfluctuaHonswithguaranteeingthe5-sigmaconfidencelevel,secureQKDoverabout90kmispossiblewithareasonablenumberofsignaltransmissions.

Modula,ondevicesF.Xuetal.,PRA92,032305(2015).Phaseinterval:


Conclusions&Outlook

Ø  Devicecharacteriza,onsonmodula,ondevices:1.RemovetheIIDassump,on.2.IntervalsarethesufficientcondiHonandnodetailedcharacteriza,onisneeded,suchasanerrordistribuHonandtheindependenceamongtheactualphasesandintensiHes.

Ø  Applica,ontoanotherQKDseVng:Toapplyourtheorytoanothersetng,saytheMDIsetng.

Ø  Highperformance:LongdistantsecureQKDispossibleupto(withpulseemissions)

intensityandphaseintervals.

withrealisHcassumpHonsonthemodulaHondevicesof

Ø  Experimentalschemeforthecharacteriza,on:Howtoguaranteethephaseandintensityintervalsareimportantfutureworks.

towards secure qkd with testable assump6ons on modula6on

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