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WP 3 WP 3 – Quantum Repeaters Časlav Brukner Institute of Quantum Optics and Quantum Information (IQOQI) Vienna & University of Vienna

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Relation to other WP‘s within QAP

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Workpackages

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WP3.1 Quantum Channels OEAW,UNIGE,LMU,UG Milestones: M3.1.1 See two-photon interference signal after transmission of photons through >500m fibre (month 12) M3.1.2 Successful transmission of entanglement over >5km free- space link (month 9) Deliverables: D3.1.1 Comparison of fiber and free-space transmission of qubits (month 12) UNIGE part of 3.3

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Free-Space distribution of entanglement and single photons over 144 km, R. Ursin, F. Tiefenbacher, T. Schmitt-Manderbach, H. Weier, T. Scheidl, M. Lindenthal, B. Blauensteiner, T. Jennewein, J. Perdigues, P. Trojek, B. Ömer, M. Fürst, M. Meyenburg, J. Rarity, Z. Sodnik, C. Barbieri, H. Weinfurter, A. Zeilinger, submitted In collaboration with: Entanglement over 144km free-space

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La Palma - Tenerife Results Bell S-Value: S=2,508+-0,037 in 221 sec. QKD Results: QBER 4,8% 178 secret bits in 75 sec. Link performance :

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Milestones: M3.2.1 Demonstration of narrow band bright time-bin entangled photon source (month 6) M3.2.2 Demonstration of polarization entanglement from ps-pulsed lasers (month 12) Deliverables: D3.2.1 Narrowband, bright entangled photon pair sources (12 month) WP3.2 Advanced sources of entangled photon pairs CNRSGRE OEAW UNIGE UBRISTOL Elsag KTH IDQUAN ULB

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Time-bin entangled sources UNIGE: Demonstration of a narrow-band bright time-bin entangled source based on PDC in periodically poled Lithium niobate waveguides and fibre bragg grating filters for the PDC photons at 10pm. Two-photon excitation of an excitonic transition in a single CdSe/ZnSe quantum dot. Current problems: the excitation is not resonant. CNRSGRE

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parameters: ~ 25 mW violet laser diode ~ detected 805 nm ~ 94% visibility of quantum correlations ~ 30% coincidence/single count ratio used in advanced undegraduate lab courses at LMU course schedule: theory of parametric down-conversion basics of state analysis preparation of distinct Bell states measurement of correlation function in complementary bases (visibility) violation of Bell inequality measurement of density matrix (fidelity of quantum state, entanglement witness, Peres-Horodecki criterium) Advanced sources

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Experiment Spectra Photonic Crystal Fibre Source Coincidences~ s -1

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HOM experiment using bright fibre sources 80 four-fold coincidences per sec.

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Fidelity 89% with pure entangled state Tomography 6000 pairs per sec Bright entangled pair source in microstructured fibre

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Further developments Periodically poled twin hole fiber as source of photon pairs. Based on fiber optic source producing pairs at telecom wavelengths based on parametric down conversion. Preliminary results: coincidences UB collaboration with Southampton University KTH Asynchronous sources of heralded single photons at 1550nm

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WP3.3 Long distance fiber-optic quantum relays and purification OEAW,UNIGE,UBRISTOL,KTH,UG Milestones: M3.3.1 Remote Bell-state analysis achieved (month 9) M3.3.2 Two remote sources of entanglement operating synchronously (month 12) Deliverables: D3.3.1 Locking of remote lasers (month 12)

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1: EPR 2: Distribute 3: Create Qubit 4: Prepare BSM 5: BSM 6: Send result 7: Store photon 8: Wait for BSM 9: Analysis Real World Q Teleportation Distance: 550 m Fibre: 800m O. Landry et al., quant-ph/

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Heralded Photon Q Teleportation Laser fs LBO & PC n n+1 n n m Only those events that are coincident with the 4 th photon are considered V raw =0.87+/-0.07 F raw =0.93+/-0.04 O. Landry et al., quant-ph/

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Detect 3 of 4 Bell states Only requires two detectors and No auxiliary photons Compatible with polarisation encoding Teleportation F = 76% J. A. W. van Houwelingen et al., Phys. Rev. A, 74, (2006) 3- Bell-State Measurement teleportation

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Quantum Memory first successes (Lukin, Kimble) Entanglement Purification fidelity F > 0.9 from 2 pairs of F = 0.75 purification above local realism threshold Pan et al., al, Nature 423, 417 (2003) Walther et al., PRL 94, (2005) Entanglement swapping teleportation of entanglement fidelity F > 0.9 (sufficient to violate Bell ‘ s inequality) Jennewein et al. PRL 88, (2002), quant/ph de Riedmatten et al., quant/ph ? Locking independent & remote lasers

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2,5 m 1 km electronic signal 80 MHz loop gain 720 MHz loop gain Electronic synchronization fs Laser I fs Laser II Electronic synchronization of lasers UG

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V~83% Visibility independent, spatially separated single-photon sources electronically synchronized fs mode locked lasers with a timing jitter of 260 fs prototype technology for quantum networking and quantum computing R. Kaltenbaek, B. Blauensteiner, M. Zukowski, M. Aspelmeyer, A. Zeilinger, PRL 96, (2006) HOM with independent lasters UG

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WP3.3 Terrestrial and satellite free-space quantum communication OEAW,LMU,UBRISTOL Milestones: M3.4.1 Single link Bell-state analysis (month 6) (correlations are measured at Tenerifa – move to next period?) M3.4.2 Measurement of single photons reflected off a ranging satellite (month 12) Deliverables: D3.4.1 Specification of requirements of entanglement sources on satellites (month 9)

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P. Villoresi et al.: Space-to-ground quantum- communication, quant-ph/ ; P. Villoresi et al.: Experimental demonstration of a quantum communication channel from a LEO satellite to Earth, to be published Laser- Ranging Station 5860 km Single photons from a Satellite 700-ps pulse 17 kHz repetition rate 0.1 photon

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WP3.5 Creation of entangled states of single atoms and photons by interference USTUTT Milestones: M3.5.1 Evaluation of production yield for different ion implantation strategy (month 6) APPLIED PHYSICS LETTERS 88 (2), (2006) M3.5.2 Evaluate the defect positioning accuracy (month 8) APPLIED PHYSICS A-MATERIALS SCIENCE & PROCESSING, 83 (2) (2006) Deliverables: D3.4.1 Writing NV defect patterns in type IIa diamond (month 9) JOURNAL OF PHYSICS-COND MAT 18 (21), 807-S824 (2006), PRL 97 (8) (2006)

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Entangling paramagnetic solid state systems voltage Laser Detuning, GHz 30 Center B Center A P. Tamarat, PRL 97 (8): Art (2006) AB Create,e.g. |0> A |1> B + |1> A |0> B by raman transitions. Solids: inhomogeneous broadening detunes A and B external compensation field. A B Fault-tolerant repeater scheme with 2 Qbits per node: MD Lukin et al. PRL 96 (7): (2006)

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Electron nuclear spin entanglement * * * Coop. with MD Lukin (Harvard) L. Childress et al. Science DOI: /science Entanglement between electron and nuclear spins. Robustness of nuclear coherence during measurement on electron spin time / s Ramsey fringes of single nuclear spin coupled to electron spin: Free evolution After measurement on electron spin

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Future ? WP 3.1 Quantum Channels Demonstration of a mobile polarization entangled photon source (Vienna) WP3.2 Advanced sources of entangled photon pairs Polarisation entangled photon source operating at telecom wavelengths (Vienna) Demonstration of a colinear, wavelength non-degenerate polarization entangled photon source (Vienna) WP 3.3 Long distance fiber-optic quantum relays and purification M: Demonstration of the robustness of polarisation entanglement over long distance fiber transmission (>50 km) (Vienna) M: Locking of independent lasers separated by > 100 m (Vienna, 24 month) M: Synchronisation of ps lasers. (Geneva, 18 month) D: HOM dip between independent ps pumped entanglement sources. (Geneva, 24 month) WP 3.4 Terrestrial and satellite free-space quantum communication M Single link Bell-state analyses (old one!) (Vienna) Analyze the influence of tracking on quantum communication in a satellite-ground link (Vienna) WP 3.5 Creation of entangled states of single atoms and photons by interference M1 Evaluate optimum method to generate electron-nuclear spin coherence. (Stutt, Period1+6) M2 Evaluate robustness of nuclear spin coherence during measurement on electron spin. (Stutt, Period1+9) D Swap of electron spin coherence and entanglement to nuclear spins. (Stutt, Period1+12)

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WP 3.5 Deliverables + Milestones M3.5.1 Evaluation of production yield for different ion implantation strategy (due: month 6) APPLIED PHYSICS LETTERS 88 (2): Art. No (2006) M3.5.2 Evaluate the defect positioning accuracy (due: month 8) APPLIED PHYSICS A-MATERIALS SCIENCE & PROCESSING, 83 (2): (2006) D3.5.1 Writing NV defect patterns in type IIa diamond (due: month 9) JOURNAL OF PHYSICS-COND MAT 18 (21): S807-S824 (2006) PRL 97 (8): Art (2006)

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ULB contribution to WP3.2 We have demonstrated a source of photon pairs based on parametric fluorescence in periodically poled twin hole fibers NBH As far as we know this is the only kind of fiber optics source of photon pairs that uses a chi_2 non linearity. If the source can be made more narrow band, it would be particularly useful for fiber optics quantum communication systems. Work on improving the source is under way. (This is a collaboration with Southampton University, where the samples are manufactured). No need to report the following: We have studied the possibility of using vector modulational instability in photonic crystal fibers as bright tunable fiber optics source of photon pairs. During preliminary work, we noticed some unexpected non linear effects that were reported in NHB2-06. Their relevance for such sources is under study.

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Entangled photons for relays M Demonstration of polarization entanglement from ps-pulsed lasers Achieved : Fulconis et al, Nature Photonics submitted D Narrowband, bright entangled photon pair sources In preparation: due m12

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ISS (International Space Station) ~400km from ground OGS (ESA) Tenerife - Spain Calar Alto - Spain 1400km distance Columbus Module (ESA) WP 3.1 Space Quest

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Time-bin entanglement sources Two-photon excitation of an excitonic transition in a single CdSe/ZnSe quantum dot. The green line is the frequency doubled laser frequency. In the middle trace the excitation is on resonance. In the top (bottom) trace the excitation is above (below) resonance and the second harmonic generation by the bulk crystal can be seen. This set of traces shows that this excitation is not resonant.

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WP 3.1 Space-QUEST Schedule: EM/EQM:2010 Lunch:2011 Experiment: 2012 Entanglement in Space

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