030516 Toni Heugel Max Kessler Violation of Bell inequality using photons 1 Theoretical Introduction Bell inequalities General Experimental Setup Detailed Setup and technical Difficulties ID: 789622
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Slide1
Violation of Bell inequalities using photons
03.05.16
Toni Heugel, Max Kessler, Violation of Bell inequality using photons
1
Slide2Theoretical Introduction – Bell inequalitiesGeneral Experimental Setup
Detailed Setup and technical DifficultiesThe Source – Generation of photons and entanglement
Detection – Beamsplitters and PhotomultipliersResultsOutlook03.05.16
Toni Heugel, Max Kessler, Violation of Bell inequality using photons
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Overview
Slide3Theoretical Introduction – Bell Inequalities
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Toni Heugel, Max Kessler, Violation of Bell inequality using photons3
Brunner et al., 2013, Bell
nonlocality
Slide403.05.16
Toni Heugel, Max Kessler, Violation of Bell inequality using photons
4
Introduction – What is a Bell Experiment?
Brunner et al., 2013, Bell
nonlocality
Test of local realistic theories
Alice
Bob
Slide5Properties of a local realistic theoryLocality: outcomes of Alice do not depend on inputs of Bob and vice versa
Reality: value of observables is determined independent of measurementProperties of quantum mechanics
Locality: üReality: ûValue of observable only manifests itself in (certain) measurement
Outcomes not completely predetermined
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Toni Heugel, Max Kessler, Violation of Bell inequality using photons
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Introduction – Local Realism
Slide6Input: direction of polarization measurement
Output: measurement result
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Toni Heugel, Max Kessler, Violation of Bell inequality using photons
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Introduction – the CHSH Inequality
Alice
Bob
Input: direction of polarization measurement
Output: measurement result
Slide7General Experimental Setup
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Toni Heugel, Max Kessler, Violation of Bell inequality using photons7
Aspect
et al., 1981, Phys.
Rev
.
Lett
. 49, 91
Slide803.05.16
Toni
Heugel, Max Kessler, Violation of Bell inequality using photons
8General Experimental Setup
Aspect
et al., 1981, Phys.
Rev
.
Lett
. 49, 91
Slide9Detailed Setup and Technical Difficulties
03.05.16
Toni Heugel, Max Kessler, Violation of Bell inequality using photons
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www.thorlabs.com
Aspect
et al., 1981, Phys.
Rev
.
Lett
.
47
, 460
Slide10Detailed Setup and Technical Difficulties
Generation of Photons
03.05.16Toni Heugel, Max Kessler, Violation of Bell inequality using photons10
www.wikipedia.org
Slide1103.05.16
Toni Heugel, Max Kessler, Violation of Bell inequality using photons
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Experimental Setup – Generation of Photons
Energy levels of Calcium
Schematic of photon generation
Aspect
et al., 1981, Phys.
Rev
.
Lett
.
47
, 460
Photon source
Slide12Beam of atomsTwo lasers
Pump atom to upper level
Two-photon absorptionOptical elements to focus photons03.05.16Toni Heugel, Max Kessler, Violation of Bell inequality using photons
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Experimental Setup – Generation of Photons
Schematic of photon generation
Slide13Isotropic emission of photonsReflection at optical elements
“wrong” photonsResonance trapping
03.05.16Toni Heugel, Max Kessler, Violation of Bell inequality using photons13
Experimental Setup – Technical Difficulties
Slide14Enforce locality (in special relativity)
Space-like separation of measurements
Detection of Bob’s output outside of lightcone of generation of Alice’s inputNo influence possibleIn ExperimentSeparation between measurements (~10
2 m)Fast measurement process (~µs)
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Toni Heugel, Max Kessler, Violation of Bell inequality using photons
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Experimental Setup –
Spacelike
Separation of Measurements
Slide15Detailed Setup and Technical Difficulties
Measurement and Polarization
03.05.16Toni Heugel, Max Kessler, Violation of Bell inequality using photons
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www.thorlabs.com
Slide16Thank you for your attention.
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Toni Heugel, Max Kessler, Violation of Bell inequality using photons16
https://xkcd.com/1591/
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Toni Heugel, Max Kessler, Violation of Bell inequality using photons
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Aspect
et al., 1981, Phys.
Rev
.
Lett
. 49, 91
Detection
Slide18Measurement observable:
P
±±(a,b): Probability to obtain the result ±1 along a and result ±1 along b
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Toni Heugel, Max Kessler, Violation of Bell inequality using photons
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Experimental Setup – Detection
+P
––
(
a,b
)
–
P
+–
(
a,b
)
–
P
–
+
(
a,b
)
Aspect
et al., 1981, Phys.
Rev
.
Lett
. 49, 91
Slide1903.05.16
Toni Heugel, Max Kessler, Violation of Bell inequality using photons
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Experimental Setup – Detection
+P
––
(
a,b
)
–
P
+–
(
a,b
)
–
P
–
+
(
a,b
)
Repeat the measurement to get
P
±±
(
a,b
)
calculate
E(
a,b)
Do this for all combinations of (
a,a
‘), (b,b
‘) calculate S
Aspect et al., 1981, Phys. Rev. Lett. 49, 91
Slide2003.05.16
Toni Heugel, Max Kessler, Violation of Bell inequality using photons
20Experimental Setup – Detection
How are the measurements performed?
First
attempts
:
Click: +1
No click: -1
Problem: not every photon is detected
Aspect
et al., 1981, Phys.
Rev
.
Lett
. 49, 91
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Toni Heugel, Max Kessler, Violation of Bell inequality using photons
21Experimental Setup – Detection
Improvement: Use a polarizing beamsplitter
Aspect
et al., 1981, Phys.
Rev
.
Lett
. 49, 91
Slide22Thin film polarizer
Faces are antirefelction coatedPhotons polarized in the incident plane are transmitted, orthogonal polarization is reflectedT||
and R are close to 1, T and R|| are close to 0Mounted in a rotating mechanism to change the measurement basis 04.05.16
Toni Heugel, Max Kessler, Violation of Bell inequality using photons
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Experimental Setup – Detection
Polarizing Beamsplitter
www.semrock.com
Slide2303.05.16
Toni Heugel, Max Kessler, Violation of Bell inequality using photons
23Experimental Setup – Detection
Photomultiplier:
Only a small subset of the emitted photons are detected
Fair sampling assumption:
Sample of detected pairs is representative for the emitted pairs.
But this assumption could be wrong
Detection loophole
Slide24Coincidence window: 20 ns
Large compared to lifetime all true coincidences are measuredAccidental coincidence rates are infered by the single ratesRtrue
=Rtot–Racc03.05.16
Toni Heugel, Max Kessler, Violation of Bell inequality using photons
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Experimental Setup – Detection
Aspect
et al., 1981, Phys.
Rev
.
Lett
. 49, 91
Slide25Results
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Toni Heugel, Max Kessler, Violation of Bell inequality using photons25
Aspect
et al., 1981, Phys.
Rev
.
Lett
. 49, 91
Slide26Measured value: Sexp
=2.697±0.015 strong violation of Bell‘s inequalitiesQM-theoretical value: SQM=2.70±0.05 because of a fidelity of 0.984
No auxiliary measurements are necessaryNon-locality loophole was ruled out by G. Weihs, T. Jennewein, C. Simon et al.Detection loophole is still open04.05.16
Toni Heugel, Max Kessler, Violation of Bell inequality using photons
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Results
Aspect
et al., 1981, Phys.
Rev
.
Lett
. 49, 91
Slide27D. N. Matsukevich, P. Maunz, D. L Moehring. et al. showed the violation of Bell‘s inequality with two remote atomic qubits
M. Ansmann, H. Wang, R. C. Bialczak et al. Showed the violation of Bell‘s inequality in Josephson phase qubits
04.05.16Toni Heugel, Max Kessler, Violation of Bell inequality using photons
27Outlook
Detection loophole was closed in other experiments:
Both experiments did not rule out the non-locality loophole
B.
Hensen
et al. reported a loophole free Bell violation using electron spins separated by 1.3 km
Slide28A. Aspect,
P. Grangier, G. Roger et al., Phys. Rev. Lett.
49, 91 (1982)G. Weihs, T. Jennewein, C. Simon et al., Phys. Rev. Lett. 81, 5039 (1998)D. N. Matsukevich
, P. Maunz, D. L Moehring. et al., Phys. Rev. Lett.
100
, 150404 (2008
)
M.
Ansmann
, H. Wang, R. C.
Bialczak
et al
.,
Nature
461
, 504 (2009
)
B.
Hensen
et al.,
Nature
526, 682–686 (29 October 2015)04.05.16Toni Heugel, Max Kessler, Violation of Bell inequality using photons28References