Towards secure QKD with testable assump6ons on modula6on devices Akihiro Mizutani 1 Collaborators: Yuichi Nagamastu 1 , Marcos Curty 2 , Hoi-Kwong Lo 3 , Koji Azuma 4 , Rikizo Ikuta 1 , Takashi Yamamoto 1 , Nobuyuki Imoto 1 , Kiyoshi Tamaki 4 1 Osaka University 2 University of Vigo 3 University of Toronto 4 NTT Basic Research Laboratories
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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
PhasemodulatorLaser Detector
OpHcalpulsesBobAlice
K.Tamakietal.,Phys.Rev.A90,052314(2014).
GLLPanalysis Loss-tolerantprotocol
Themainidea:UHlizingthe“basismismatchedevents”toesHmateEve’sleakedinformaHon.
Loss-tolerantprotocolØ Loss-tolerantprotocol
PhasemodulatorLaser Detector
OpHcalpulsesBobAlice
K.Tamakietal.,Phys.Rev.A90,052314(2014).
TheLTprotocolassumesthatthephasemodulaHonerrorsfollowIID.
IIDdistribuHononmodulaHondevice
・・・
Loss-tolerantprotocol
PhasemodulatorLaser Detector
OpHcalpulsesBobAlice
K.Tamakietal.,Phys.Rev.A90,052314(2014).
Hardorevenimpossibletoconfirmintheexperiment.
TheLTprotocolassumesthatthephasemodulaHonerrorsfollowIID.
Ø Loss-tolerantprotocol
Loss-tolerantprotocol
PhasemodulatorLaser Detector
OpHcalpulsesBobAlice
K.Tamakietal.,Phys.Rev.A90,052314(2014).
WeneedmorerelaxedassumpHonsonthesource.
TheLTprotocolassumesthatthephasemodulaHonerrorsfollowIID.
Hardorevenimpossibletoconfirmintheexperiment.
Ø Loss-tolerantprotocol
Loss-tolerantprotocol
PhasemodulatorLaser Detector
OpHcalpulsesBobAlice
K.Tamakietal.,Phys.Rev.A90,052314(2014).
TowardssecureQKDwithtestableassumpDonsonmodulaDondevices(seearXivsoon!)
Hardorevenimpossibletoconfirmintheexperiment.
TheLTprotocolassumesthatthephasemodulaHonerrorsfollowIID.
WeneedmorerelaxedassumpHonsonthesource.
Ø Loss-tolerantprotocol
CharacterizaHonofmodulaHondevices
Phaseinterval Taggedpulses Failureprobability
AllthepulsesemiWedwithPhasemodulator:
• Untaggedsignal:Pulsewhosephaseliesintheinterval• Taggedsignal:Pulsewhosephasedoesnotlieintheinterval
Phasemodulator
Laser DetectorOpHcalpulses
Intensitymodulator
Ø Loss-tolerantprotocol
CharacterizaHonofmodulaHondevices
Phaseinterval Taggedpulses Failureprobability
AllthepulsesemiWedwith
…Ø Non-IIDmodulaHonerrorsareaccommodated.
Ø IntervalsarepotenHallytestableinexperiments.
Phasemodulator:
Phasemodulator
Laser DetectorOpHcalpulses
Intensitymodulator
Ø Loss-tolerantprotocol
CharacterizaHonofmodulaHondevices
Intensitymodulator:
Phaseinterval Taggedpulses Failureprobability
AllthepulsesemiWedwithPhasemodulator:
Intensityinterval Taggedpulses Failureprobability
AllthepulsesemiWedwith
Ø Taggedeventsoccurindependentlyof
Phasemodulator
Laser DetectorOpHcalpulses
Intensitymodulator
Ø Loss-tolerantprotocol
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:
Intensityinterval(±3%):
=Probability(perpulse)ofbeingoutsidetheinterval
(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).
=Probability(perpulse)ofbeingoutsidetheinterval
NoHceEvenifweassume±5%intensityfluctuaHonswithguaranteeingthe5-sigmaconfidencelevel,secureQKDoverabout90kmispossiblewithareasonablenumberofsignaltransmissions.
Modula,ondevicesF.Xuetal.,PRA92,032305(2015).Phaseinterval:
Intensityinterval(±5%):
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.
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