GAP Optique Geneva University 1 Quantum Communication  With 1 photon: Q cryptography  With 2 photons: Q crypto, Bell tests, qutrits, plasmons  With 3 photons: Q teleportation  With 4 photons: entanglement swapping  News from the industry forehead Nicolas Gisin Hugo Zbinden, Ivan Marcikic, Hugues de Riedmatten, Sylvain Fasel, Jeroen van Houwelingen, Rob Thew Group of Applied Physics, University of Geneva

GAP Optique Geneva University 2 Q communication in optical fibres  The transmission depends on the wavelength - Lower attenuation : 1310 nm (0.3 dB/km) and 1550 nm (0.2dB/km) (telecom wavelengths) Two problems : Losses and decoherence. How to minimize them ?  Time-bin coding with  Decoherence due to birefringence : Polarization Mode Dispersion photons at telecom wavelength

GAP Optique Geneva University 3 Time-bin qubits  qubit :  any qubit state can be created and measured in any basis variable coupler variable coupler 1 0   h AliceBob D 0 D 1 switch 1 0 State preparation Projective measurement W. Tittel & G. Weihs, Quant. Inf. Comput. 1, Number 2, 3 (2001)

GAP Optique Geneva University 4 B 0 A 0 1 B 1 A    Detectors & Coincidence   Time-bin entanglement PDC  Laser Variable coupler Robust against decoherence in optical fibers After 2x2km of optical fibers 2 km optical fibers V net =96%.Photon pair creation in a non-linear crystal.Parametric down-conversion (PDC).Energy and momentum conservation p =710nm s =1310nm i =1550nm R. Thew et al., Phys. Rev. A 66, (2002)

GAP Optique Geneva University 5 1-photon: Q crypto AliceBob km Results: (PRA 63,012309, 2001 and S. Fasel et al., EJPD 30, 143, 2004) CDC IF Asynchronous heralded single-photon source Time between a click at detector A and a click at detector B [# trigger signals] Number of events (normailzed) P(1 )=60% P(2 )=0.02% g (2) (0)= KHz (quant-ph/ )

GAP Optique Geneva University 6 2-photons: Bell test over 50 km Bob Alice Time arrival on A 1 Time arrival on B 1 = short path = long path Type I NLC Creating 1.3 & 1.55  m deterministic sepation with WDM coupler

GAP Optique Geneva University 7  Idea: verify from time to time the phase Stabilisation of the interferometers Every 100 s the phase is brought back to a given value

GAP Optique Geneva University 8 Bell test over 50 km  With phase control we can choose four different settings  = 0 ° or 90 ° and  = -45 ° or 45 °  Violation of Bell inequalities: Violation of Bell inequalities by more than 15  Marcikic et al., PRL, in press, quant-ph/

GAP Optique Geneva University 9 2-photons: Qutrit Entanglement

GAP Optique Geneva University 10 Bell Violation with qutrits I = / I(lhv) = 2 < I(2) = < I(3) = 2.872

GAP Optique Geneva University 11 2-photons: Plasmon assisted entanglement transfer In collaboration with Prof. Erni, Zürich  a short lived phenomenon like a plasmon can be coherently excited at two times that differ by much more than its lifetime. At a macroscopic level this would lead to a “Schrödinger cat” living at two epochs that differ by much more than a cat’s lifetime.

GAP Optique Geneva University 12 3 photons: Q teleportation & Q relays  EPR  Bell 2 bits U  J. D. Franson et al, PRA 66,052307,2002 Collins et al., quant-ph/

GAP Optique Geneva University 13 Q repeaters & relays * entanglement * Bell measurement.. QND measurement + Q memory * entanglement * Bell measurement. ?? REPEATER RELAY H. Briegel, W. Dür, J. I. Cirac and P. Zoller, Phys. Rev. Lett. 81, 5932 (1998) J. D. Franson et al, PRA 66,052307,2002; D. Collins et al., quant-ph/

GAP Optique Geneva University 14 2 km of optical fiber Alice Alice:creation of qubits to be teleported Alice 55 m Bob Bob:analysis of the teleported qubit, 55 m from Charlie Bob Charlie Charlie:the Bell measurement Charlie fs 710 nm Experimental setup creation of entangled qubits coincidence electronics & LBO RG WDM RG WDM Ge InGaAs LBO BS InGaAs f s l a s e r sync out 1. 3 m  1. 3 m  1. 5 m  1. 5 m  2km H. de Riedmaten et al., PRL 92, /4, 2004 I. Marcikic et al., Nature, 421, , 2003

GAP Optique Geneva University 15results Equatorial states Raw visibility : V raw = 55 ± 5 % = 77.5 ± 2.5 % = 78 ± 3% = 77 ± 3% North & south poles mean fidelity: F poles =77.5 ± 3 % 77.5 ±2.5 % Mean Fidelity » 67 % (no entanglement)

GAP Optique Geneva University 16 2 km of optical fiber Alice Alice:creation of qubits to be teleported Alice 55 m Bob Bob:analysis of the teleported qubit, 55 m from Charlie Bob Charlie Charlie:the Bell measurement Charlie fs 710 nm Experimental setup creation of entangled qubits coincidence electronics & LBO RG WDM RG WDM Ge InGaAs LBO BS InGaAs f s l a s e r sync out 1. 3 m  1. 3 m  1. 5 m  1. 5 m  2km H. de Riedmaten et al., PRL 92, /4, 2004 On the same spool ! See Halder et al quant-ph/

GAP Optique Geneva University 17 4-photons: Entanglement swapping Bell state measurement Entangled photons that never interacted EPR source

GAP Optique Geneva University 18 Sources of time-bin entangled photons The experiment Bell state measurement Entanglement analysis Actively stabilized interferometers  1km

GAP Optique Geneva University 19 In the experiment :Partial Bell state measurement Entanglement swapping Four Bell states involved in the experiment !

GAP Optique Geneva University 20 Superposition basis: results V = (80 ± 4) % F  90 % 78 hours of measurement !

GAP Optique Geneva University 21 Results: computational basis Mean Fidelity =

GAP Optique Geneva University 22 News from the industry forehead Yesterday, September 29, id Quantique, DeckPoint and the University of Geneva officially inaugurated the first data archive site secured with Quantum Cryptography.

GAP Optique Geneva University 23 Data archiving network secured by Quantum Crypto  10 km

GAP Optique Geneva University 24 Quantis: Quantum random numbers on demand ( 4 Mbit/s per module, up to 4 modules on one PC card 1 light source 1 beam splitter 2 photon counters in a few cm 3 (  4x5x1 cm 3 ) !!! www. idquantique.com

GAP Optique Geneva University 25 Few « qubit » Applications Photon-counting OTDR Coherent Q measurement of the degree of polarization: symbole plein: polarimètre symbole vide: projection sur  (-) DOP=1 DOP=0.74 DOP=0.34 DOP temps(s) J.Lightwave Tech, 2, 390, 2004 PRL 91, , 2003

GAP Optique Geneva University 26 Conclusions Where are the applications? Next September 29, id Quantique, DeskPoint and the University of Geneva will officially inaugurate the first data archive site secured with Quantum Cryptography.

GAP Optique Geneva University 27 Single Photon Sources 919 nm / 0.7 nm 650 nm / >50 nm 1550 nm / 7nm /  Quantum Dot NV High pump Low pump g (2) (0) [%] P 2 [%] P 1 [%] 76 MHz5.3 MHz803 kHz34 kHzNTNT Beveratos et. al., PRL 89, (2002) Vuckovic et. al., APL 82, 3596 (2003) Fasel et. al. in preparation

GAP Optique Geneva University 28 Size of the classical communication One proton in one cm 3 at a temperature of 300 K:  bits protons in one cm 3 at a temperature of 300 K  x 155  bits To be compared to today’s optical fiber communication in labs: 1 Tbyte x 1024 WDW channels x 1000 fibers  bits/sec.   1 hour !! bits

GAP Optique Geneva University 29 entangled time-bin qubit  variable coupler non-linear crystal B s A s l B l A depending on coupling ratio and phase , maximally and non-maximally entangled states can be create d R. Thew et al, PRA 66, , 2002 Extensions to entanglement in higher dimensions: - qutrits: R. Thew et al, quant-ph/ up to dimesnion 20: H. Deriedmatten et al, quant-ph/

GAP Optique Geneva University 30 Bell state measurement H. Weinfurter, Europhysics Letters 25, (1994) H. de Riedmatten et al., Phys. Rev. A 67, (2003) 1 2 A B