Experimental Non Locality Proof of Quantum Teleportation and Entanglement Swapping
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Transcript of Experimental Non Locality Proof of Quantum Teleportation and Entanglement Swapping
8/3/2019 Experimental Non Locality Proof of Quantum Teleportation and Entanglement Swapping
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Experimental Nonlocality Proof of Quantum Teleportation andEntanglement Swapping
Thomas Jennewein, Gregor Weihs,Jian-Wei Pan, Anton Zeilinger
PRL 88, 017903-2(2002)
This work was supported by the AustrianScience Fund (FWF) and the “QuComm”IST-FET project of the EuropeanCommission.
8/3/2019 Experimental Non Locality Proof of Quantum Teleportation and Entanglement Swapping
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Entangled Photons
n Not factorizablen Strong correlations between the systemsn Individual systems have no properties, only joint properties
( )
( )
( )2121
2121
2121
2
1
21
2
1
+---+=
=-=
=-=
R LLR
H V V H y One of fourBell-states
-
8/3/2019 Experimental Non Locality Proof of Quantum Teleportation and Entanglement Swapping
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Correlation Measurement
Correlation: E( a , b ) = P ++ + P -- - P + - - P - + = - cos(2 a -2 b ) always perfect anticorrelations for parallel Analyzers ( a = b).
( ) ( ) ( )b a b a b a -== --++2sin
2
1,, P P
( )H V V H -=2
1y
Source
-
a b
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Bell’s InequalityBased on EPR: Locality and Realism
Locality: Particles act independtly in measurementRealism: Carried information ( l ) defines result
CHSH-Inequality:
( ) ( ) 2,,),(),( £¢¢+¢+¢- b a b a b a b a E E E E
QM: E( a , b ) = - cos(2 a -2 b )
222 £ /
8/3/2019 Experimental Non Locality Proof of Quantum Teleportation and Entanglement Swapping
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Source of Entangled Photonsn Spontaneous Parametric Down-conversion
n non-linear optical process ( c2)n one UV-photon decays into two new photons
obeying energy and momentum conservation
extra ordinary(vertical)
ordinary(horizontal)
BBO-Crystal
UV-
Pump
+| Ò | ÒH VA A| Ò | ÒV HB B
AB
8/3/2019 Experimental Non Locality Proof of Quantum Teleportation and Entanglement Swapping
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The Bi-Photon Staten The full state
n This state resembles the |Y-Òfor a narrowpump linewidth
n Contrast is reduced for finite pumplinewidth
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Quantum State Teleportationn Quantum state is transferred between different
particles, as long as no information about thestate is found out.
n Classically impossible due to:n Heisenberg Uncertaintyn No-cloning Theorem
n Basic ingreedient for quantum repeater,quantum networks, quantum computers.
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Teleportation Scheme1993 PRL, Bennet et al. :Teleporting an unknownquantum state via dualclassical and EPR channels.
Input State
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Entanglement Swappingn The most general test of QST
n The input state is undefinedin a fundamental way
n Entanglement survivesperfectly if no information isgained
ALICE
VICTOR
Polarization Analysis
Bell-State Analyzer
EntangledPhotonSource
EntangledPhotonSource
BOB
1 2 30
Y-F+
Y-Y+F-Y-
III
Polarization Analysis
8/3/2019 Experimental Non Locality Proof of Quantum Teleportation and Entanglement Swapping
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Previous Experimentsn Bouwmeester et al, Nature (1997)
n Teleportation of a well defined input staten
Observed visibility: ~ 70% ± 3%n Pan et al., PRL (1998)
n Entanglement swappingn Observed visibility: ~ 65 % ± 2%
n Violation of Bell‘s inequality requires atleast 71 %!
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Experimental Setupn Pulsed
downconversion fortwo pairs
n UV Pulses: 200 fs,76 MHZ, 394 nm
n 1 event in 100sn Single mode fibersn Correlation:
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Active Beam Stabilizationn CCD measures beam positionn two motorized mirrors steer the beam
0 3 6 9 12 150,0
0,10,2
0,3
0,4
0,5
0,6
0,7
0,8
0,9
1,0
1,1
without laser controlwith laser control
n o r m
a l i z e
d c a
l c u
l a t e d 4 - f o
l d r a
t e
Time [h]
Stability Comparison:
Stability sufficient for the required times (16000 s per point)!
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Coincidence Logicn NIM-Logic n Programmable
Logicn VHDLn Reprogrammable
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High Visibility Teleportation
n Visibility tests
n All effects limiting the visibilityconsideredn Theory:
@45° Vis=0,817@0° Vis=0,897
n Experiment:@45° Vis=0,812 ± 0,103@0° Vis=0,883 ± 0,030
8/3/2019 Experimental Non Locality Proof of Quantum Teleportation and Entanglement Swapping
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Test of Bell’s Inequalityn CHSH version of Bell‘s inequality:
n S = |E(0°,22.5°) - E(0°,67.5°)| +|E(45°,22.5°) + E(45°,67.5°)| £ 2
n Experimental test of the CHSH-inequality:n S = |-0.6281 - (+ 0.6766)| + |-0.5748 - 0.5407|
= 2.420 £ 2n DS = 0.091 -> 4.6 s above the classical limit.
n Violation of Bell‘s inequaliy for particles thatnever interacted!
(QM: S=2,82...)
8/3/2019 Experimental Non Locality Proof of Quantum Teleportation and Entanglement Swapping
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Fidelity of the Teleportation
n
QM: Relative timing of the detection events doesnot influence results (A. Peres)n In the Bell-measurements: simultaneously (2ns)n Delayed-Choice : BSA measurement delayed by 50 ns!
0,0 22,5 45,0 67,5 90,00,500,550,600,650,700,750,800,850,900,951,00
F i d
e l i t y
Bell Inequality Violation Limit
Classical Limit
FidelityFidelity with Delayed Choice
Polarizer Orientationf 0=f 3 [°]
Fidelity:
8/3/2019 Experimental Non Locality Proof of Quantum Teleportation and Entanglement Swapping
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Space-Time Arrangement for
the Entanglement Swappingn Time-ordering of detection events
Normal Entanglement Swapping: Delayed Choice:
x
t2 ns
20 ns
2 m (~ 6 ns)x
t
50 ns
20 ns
2 m (~ 6 ns)
Alice Bob
Alice
Bob
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Independence of the Photons?n The two pairs (0-1 and 2-3)
independently violate Bell‘s inequality!n
Phase drift of BS-arms would wash outany “phase coherence”.
0 2 4 6 8 10 12-20
-15
-10
-5
0
5
10
P h a s e
[ m u
l t i p l e s o
f l ]
time [h]10 100 1000
0,1
1
s ( t ) [ m
u l t i p l e s o
f l ]
t [s]
Mach-Zehnder Interferometer
Drift: 1 l with 1 s in 400 s
-> any phase relation betweenthe photons clearly washed outwithin 16000 s!
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Conclusionn Entangled Photons allow “proof of principle”
experiments in quantum information processing:n Teleportation of an entangled state shows the first violation of
Bell‘s inequality for photons that never interacted. (PRL, Vol 88,017903 (2002)).
n Additional tests adressing the timing in teleportation and theindpendence of the photons were performed.
n Outlook:n Teleportation will be enhanced with more-complete BSA and
active switching of receiver photon in a long-distanceteleportation scheme (600 m).