WP 3WP 3 – Quantum Repeaters

Časlav BruknerInstitute of Quantum Optics and Quantum Information (IQOQI) Vienna&University of Vienna

Relation to other WP‘s within QAP

Workpackages

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

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

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:

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

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

parameters:• ~ 25 mW violet laser diode • ~ 20000 detected pairs/sec @ 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

Experiment

Spectra

Photonic Crystal Fibre SourceCoincidences~3.105 s-1

HOM experiment using bright fibre sources

80 four-fold coincidences per sec.

Fidelity 89% with pure entangled state

Tomography

6000 pairs per sec

Bright entangled pair source in microstructured fibre

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

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)

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/0605010

Heralded Photon Q Teleportation

Laser fs

LBOLBO

&

PCnn+1

nn+1

200 m200 m

Only those events that are

coincident with the 4th photon

are considered

Vraw

=0.87+/-0.07

Fraw

=0.93+/-0.04

O. Landry et al., quant-ph/0605010

0 180 360 540 720 900 1080 12600

100

200

300

400

500

600

700

Th

ree

-fo

ld c

oin

cid

an

ces

(pe

r 4

.4h

, co

rre

cte

d)

Phase (degrees)

D1

D2

t =

b

e

f

a

t 1 t 0

t 1 t 0

t 2

+

+

-

-

D2D1 00 0122 1211 02 0

010

22

12

11

21

01

02

2000 0122 1211 02

1/16

1/16

1/16

1/16

1/16

1/16

1/16

1/16

1/4 1/4

1/8 1/81/4 1/4 1/8 1/8

1/8 1/8 1/81/8

1/2

1/81/81/8 1/8 1/8

1/81/81/8

V=51± 3%V=69±10%V=55± 3%

• 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)

e i

3- Bell-State Measurement teleportation

Quantum MemoryQuantum Memory

first successes (Lukin, Kimble)

Entanglement PurificationEntanglement 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, 040504 (2005)

Entanglement swappingEntanglement swapping

teleportation of entanglement

fidelity F > 0.9 (sufficient to violate Bell‘s inequality)

Jennewein et al. PRL 88, 017903 (2002), quant/ph 0409008

de Riedmatten et al., quant/ph 0409093

??

Locking independent & remote lasers

2,5 m1 kmelectronic signal

80 MHz loop gain

720 MHz loop gain

Electronic synchronization

fs Laser I

fs Laser II

Electronic synchronization of lasersUG

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, 240502 (2006)

HOM with independent lastersUG

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)

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

Laser- Ranging Station

5860 km

Single photons from a Satellite

700-ps pulse

17 kHz repetition rate

0.1 photon

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)

Entangling paramagnetic solid state systems

volt

age

Laser Detuning, GHz30

Center B

Center A

P. Tamarat, PRL 97 (8): Art. 083002 (2006)

01

2

1

2

A BCreate,e.g. |0>A |1>B+ |1>A |0>B by raman transitions.

Solids: inhomogeneous broadening detunes A and B external compensation field.

AB

Fault-tolerant repeater scheme with 2 Qbits per node:MD Lukin et al. PRL 96 (7): 070504 (2006)

Electron nuclear spin entanglement

** *

Coop. with MD Lukin (Harvard)

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

Entanglement between electron and nuclear spins.

Robustness of nuclear coherence during measurement on electron spin

0 10 20 30 40 50 60 700,75

0,80

0,85

0,90

0,95

1,00

1,05

pure nuclear state (light induced polarization)

Flu

ore

sce

nce

, a

. u

.

delay, s

pseudo-pure state

time /s

Ramsey fringes of singlenuclear spin coupled to electron spin: Free evolution

After measurement on electron spin

Future ?WP 3.1 Quantum ChannelsDemonstration of a mobile polarization entangled photon source (Vienna)

WP3.2 Advanced sources of entangled photon pairsPolarisation 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 purificationM: 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 communicationM 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)

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)

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.

Entangled photons for relaysM 3.2.2 Demonstration of polarization entanglement from ps-pulsed lasers 

Achieved: Fulconis et al, Nature Photonics submittedD 3.2.1 Narrowband, bright entangled photon pair sources In preparation: due m12

ISS (International Space Station)~400km from ground

OGS (ESA)Tenerife - Spain Calar Alto - Spain

1400km distance

Columbus Module (ESA)

WP 3.1 Space Quest

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.

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

Entanglement in Space