GAP Optique Geneva University photon Quantum Communication Geneva University,Switzerland Group ofAppliedPhysics Nicolas Gisin splitter (entanglement) nonlocality Quantum The photon both paths explores randomness Quantum detectors 1 GAP Optique Geneva University ƒ ƒ ƒ ƒ Nature. It wouldbe absurdnottoexploit thisgiftof simulations. Numerical - Internet lotteries, - -PIN numbers,information society: This giftofNature is extremelyusefulinour Nature offersuspure randomness. source ofpurerandomness intoday’sphysics. Quantum Randomness istheonlyintrinsic Quantum Randomness 2 GAP Optique Geneva University - This canbe used inmany ways: Secret &PrivateRandomness isnothing buta Let’s exploit thisgiftofNature + H orV?The resultisrandom,butit lc Bob Alice V or - ? The result israndom, butitis ? The + H This isNonlocal SecretRandomness! Quantum Magic, Entanglement Quantum Entanglement random If AliceandBobmake the samemeasurement (both H/Vorboth+/-), Quantum Theory: then theresultis , private and secret isthesameat AliceandatBob thesame atAliceand atBob cryptographic key:QKD . - V + H . 3 GAP Optique Geneva University Plain text Plain text http://www.uqcc.org Updating Quantum Cryptography andCommunication Slide taken from the Japanese UQCC: Secret key ⊕ Quantum key distribution(QKD) QKD forencryption the plain text. the plain encode anddecode Use thekeyto QKD forencryption One-time padorAES Photons Cipher text Cipher text Secret key ⊕ Plain text Plain text 4 QKD can beused for any application that requires secret keys GAP Optique Geneva University Scheme to ensure that dataarege Scheme toensurethat Text Tag Quantum keydistribution (QKD) W.-C. Messageauthentication QKD forauthentification QKD forauthentification function togenerate thetag. choose ahash Use thekeyto Photons nuine and have not been altered. nuine andhavenotbeenaltered. Text Tag Verification 5 GAP Optique Geneva University 4 D. Stucki etal., NewJournal of Physics , 41.1-41.8, 2002. Quant-ph/0203118 QKD over67km + aerial cable (in SteCroix, Jura) ! RMP 74 , 145-195,2002 4 cm 6 GAP Optique Geneva University ƒ ƒ ƒ ƒ ƒ (Device Independent) Easier totest More protocols Longer distances Cheaper Faster Quantum Cryptography: Challenges Engineering Science 7 GAP Optique Geneva University 150 kmofinstalled fibers Long distanceQKD:Worldrecords Lausanne , OpticsExpress17 NJP 11 250 kminthelab 075003(2009) , , 13326(2009) . 8 GAP Optique Geneva University single-photon sources, it would take single-photon sources, itwould With the bestoptical fibers,perfect 100kHz 10MHz 10kHz 1MHz Rate 1kHz Key Secret 1Hz P2P +WDM 100 There isahard wallaround400 km! Distance [km] 200 Distance limitation Today Commercial Today Today Lab +4 Years 0 400 300 noise-free detectorsand ideal10GHz centuries tosend1qubit over1000 km! 9 GAP Optique Geneva University The synchronisation requires Quantum memories Entanglement Teleportation ofentanglement

Beating thehardwall: Entanglement overtwicethedistance ⇒ Q teleportation Entanglement 10 Today’s efficiencies

Nature 456 GAP Optique Geneva University photon in ≈ 20 % , 773, 2008 is nowcodedin ahugeentangledstates Quantum Memory The quantumstate ofthephoton fblin f«aos» atoms of billions« crystal doped with billions ofions Quantum Memoriesarestillin thelabs in sameQstate at desiredtime photon out 11 GAP Optique Geneva University ƒ ƒ ƒ Europe must react! detectors. detectors andfor superconducting This isthecaseboth forsemiconductor in theUnited-Sates. Today, thebest detectors areallproduced Single-photon detectors 12 GAP Optique Geneva University Quantum NetworksasManyBody Systems “spin” “spin” Simulators “interaction” “interaction” CalTec, USA Prof. H.J.Kimple Borrowed from 13 GAP Optique Geneva University ƒ ƒ ƒ ƒ - improved detectors andsources. improved - And Device Independent. Self-testing: - protocolsexploiting entanglement, more - memories, quantum - Big challenges: tomorrow’s communications. to increasethesecurity oftoday’sand Nonlocal SecretPrivate Randomness, incredible giftsofNature: However, itwould beabsurdnottoexploitthis understand. (Entanglement) ishardto Quantum “Magic” Conclusions 14