WP 3

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WP 3

• WP 3 Quantum Repeaters
• Caslav Brukner
• Institute of Quantum Optics and Quantum
  Information (IQOQI) Vienna
• University of Vienna

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Relation to other WPs 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
gt500m fibre (month 12) M3.1.2 Successful
transmission of entanglement over gt5km 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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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
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La Palma - Tenerife Results
Link performance
Bell S-Value S2,508-0,037 in 221 sec. QKD
Results QBER 4,8 178 secret bits in 75 sec.
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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)

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

• parameters
• 25 mW violet laser diode
• 20000 detected pairs/sec _at_ 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)

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Photonic Crystal Fibre Source
Coincidences3.105 s-1
Spectra
Experiment
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HOM experiment using bright fibre sources
80 four-fold coincidences per sec.
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Bright entangled pair source in microstructured
fibre
6000 pairs per sec
Fidelity 89 with pure entangled state
Tomography
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Further developments
UB

• 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
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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Real World Q Teleportation
1 EPR
2 Distribute
3 Create Qubit
4 Prepare BSM
5 BSM
6 Send result
7 Store photon
8 Wait for BSM
9 Analysis
Distance 550 m Fibre 800m
O. Landry et al., quant-ph/0605010
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Heralded Photon Q Teleportation
200 m
200 m
LBO
Vraw0.87/-0.07 Fraw0.93/-0.04
Only those events that are coincident with the
4th photon are considered
O. Landry et al., quant-ph/0605010
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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, 022303 (2006)
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Locking independent remote lasers
?
Quantum Memory first successes (Lukin,
Kimble) Entanglement Purification fidelity F gt
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, 040504
(2005) Entanglement swapping teleportation of
entanglement fidelity F gt 0.9 (sufficient to
violate Bells inequality) Jennewein et al. PRL
88, 017903 (2002), quant/ph 0409008 de
Riedmatten et al., quant/ph 0409093
?
?
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Electronic synchronization of lasers
UG
fs Laser I
Electronic synchronization
80 MHz loop gain 720 MHz loop gain
fs Laser II
electronic signal
1 km
2,5 m
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HOM with independent lasters
UG

• 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

V83 Visibility
R. Kaltenbaek, B. Blauensteiner, M. Zukowski, M.
Aspelmeyer, A. Zeilinger, PRL 96, 240502 (2006)
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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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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/0408067 P.
Villoresi et al. Experimental demonstration of a
quantum communication channel from a LEO
satellite to Earth, to be published
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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), 023113
(2006) M3.5.2 Evaluate the defect positioning
accuracy (month 8) APPLIED PHYSICS
A-MATERIALS SCIENCE PROCESSING, 83 (2) 321-327
(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) 083002 (2006)

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Entangling paramagnetic solid state systems
Fault-tolerant repeater scheme with 2 Qbits per
node MD Lukin et al. PRL 96 (7) 070504 (2006)
A
B
2
2
1
1
0
A
B
Create,e.g. 0gtA 1gtB 1gtA 0gtB by raman
transitions. Solids inhomogeneous broadening
detunes A and B external
compensation field.
P. Tamarat, PRL 97 (8) Art. 083002 (2006)
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Electron nuclear spin entanglement
Coop. with MD Lukin (Harvard)

• Entanglement between electron
• and nuclear spins.

L. Childress et al. Science DOI
10.1126/science.1131871

• 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
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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 (gt50 km)
(Vienna) M Locking of independent lasers
separated by gt 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,
Period16) M2 Evaluate robustness of nuclear spin
coherence during measurement on electron spin.
(Stutt, Period19) D Swap of electron spin
coherence and entanglement to nuclear spins.
(Stutt, Period112)
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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.
023113 (2006) M3.5.2 Evaluate the defect
positioning accuracy (due month 8) APPLIED
PHYSICS A-MATERIALS SCIENCE PROCESSING, 83 (2)
321-327 (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. 083002 (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 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.

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Entangled photons for relays
M 3.2.2 Demonstration of polarization
entanglement from ps-pulsed lasers  Achieved
Fulconis et al, Nature Photonics submitted D
3.2.1 Narrowband, bright entangled photon pair
sources  In preparation due m12
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WP 3.1 Space Quest
ISS (International Space Station) 400km from
ground
Columbus Module (ESA)
1400km distance
Calar Alto - Spain
OGS (ESA) Tenerife - Spain
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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
Entanglement in Space
Schedule EM/EQM 2010 Lunch 2011 Experiment
2012