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

2. Relation to other WP‘s within QAP

3. Workpackages

4. 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

5. Entanglement over 144km free-space
In collaboration with:
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

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

7. WP3.2 Advanced sources of entangled photon pairs CNRSGRE OEAW UNIGE UBRISTOL Elsag KTH IDQUAN ULB
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)

8. 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.
CNRSGRE
Two-photon excitation of an excitonic transition in a single CdSe/ZnSe quantum dot. Current problems: the excitation is not resonant.

9. Advanced sources ~ 30% coincidence/single count ratio 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)

10. Photonic Crystal Fibre Source
Coincidences~3.105 s-1
Spectra
Experiment

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

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

13. Further developments UB KTH
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.
collaboration with Southampton University
Preliminary results: coincidences
KTH
Asynchronous sources of heralded single photons at 1550nm

14. 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)

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

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

17. 3- Bell-State Measurement teleportation
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)

18. Locking independent & remote lasers?
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  

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

20. HOM with independent lastersUG
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
Realizing HOM visibility of entangled photons above 95% (APL, UIUC, UQ, UV)
Develop improved (current 91% visibility) pulsed (Ti:Saph) source of entangled photons, maintaining HOM visibility > 90% while reducing spectral filtering requirements, enabling multi-source interference experiments and improving the rate of generation. (APL, UIUC, UQ, UV)
V~83% Visibility
R. Kaltenbaek, B. Blauensteiner, M. Zukowski, M. Aspelmeyer, A. Zeilinger, PRL 96, (2006)

21. 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)

22. Single photons from a Satellite
Laser-
Ranging
Station
5860 km
Single photons from a Satellite
700-ps pulse
17 kHz repetition rate
0.1 photon
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

23. 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)

24. Entangling paramagnetic solid state systems
Fault-tolerant repeater scheme with 2 Qbits per node:
MD Lukin et al.  PRL 96 (7): (2006) B
voltage
Laser Detuning, GHz 3
Center B
Center A 2 2 1 1 A B
Create,e.g. |0>A |1>B+ |1>A |0>B by raman
transitions.
Solids:
inhomogeneous broadening detunes A and B
external compensation field.
P. Tamarat, PRL 97 (8): Art (2006)

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

26. 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)

27. WP 3.5 Deliverables + Milestones
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)

28. ULB contribution to WP3.2
We have demonstrated a source of photon pairs based on parametric fluorescence in periodically poled twin hole fibers NBH1-06. 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.

29. 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

30. 1400km distance ISS (International Space Station) WP 3.1 Space Quest
~400km from ground
WP 3.1 Space Quest
Columbus Module (ESA)
1400km distance
OGS (ESA)
Tenerife - Spain
Calar Alto - Spain

31. 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.

32. WP 3.1 Space-QUEST Entanglement in Space Schedule: EM/EQM: 2010
Lunch: 2011
Experiment:
EM…. Engeneering module
EQM… Engeneering qulified module (=flighmodule)