Local («classical») correlations ≠ Quantum correlations · A.Tavakoli, MO.Renou, N.Gisin,...
Transcript of Local («classical») correlations ≠ Quantum correlations · A.Tavakoli, MO.Renou, N.Gisin,...
![Page 1: Local («classical») correlations ≠ Quantum correlations · A.Tavakoli, MO.Renou, N.Gisin, N.Brunner (2017) 19 Correlations in star networks: from Bell inequalities to network](https://reader033.fdocuments.net/reader033/viewer/2022060715/607b1c8639c5ea701273cf68/html5/thumbnails/1.jpg)
Network-Locality
1
Marc-Olivier Renou
In collaboration with:
Armin Tavakoli, Denis Rosset, Yuyi Wang, Nicolas Gisin, Nicolas Brunner
![Page 2: Local («classical») correlations ≠ Quantum correlations · A.Tavakoli, MO.Renou, N.Gisin, N.Brunner (2017) 19 Correlations in star networks: from Bell inequalities to network](https://reader033.fdocuments.net/reader033/viewer/2022060715/607b1c8639c5ea701273cf68/html5/thumbnails/2.jpg)
2
A Quantum
Network:
See also research at Perimeter (Waterloo) , ICFO (Barcelona), UFRN (Natal), Neel (Grenoble) …
𝝆𝟏 𝝆𝟐 𝝆𝟓
𝝆𝟒𝝆𝟑
𝝆𝟔
𝝆𝟕
Fine Genuine
Quantum Properties?
Bell NonLocality approach:
𝝀
𝝀𝟏 𝝀𝟐 𝝀𝟓
𝝀𝟒𝝀𝟑
𝝀𝟔
𝝀𝟕
Network-Locality approach:
![Page 3: Local («classical») correlations ≠ Quantum correlations · A.Tavakoli, MO.Renou, N.Gisin, N.Brunner (2017) 19 Correlations in star networks: from Bell inequalities to network](https://reader033.fdocuments.net/reader033/viewer/2022060715/607b1c8639c5ea701273cf68/html5/thumbnails/3.jpg)
z c
C
A B
p parties
𝐴, 𝐵, 𝐶, …
q inputs
𝑥, 𝑦, 𝑧 ∈ {1,… , 𝑞}
r outputs
𝑎, 𝑏, 𝑐 ∈ {1, … , 𝑟}
1 common source:
Bell nonlocality
Behavior 𝑃 = 𝑝 𝑎𝑏𝑐 𝑥𝑦𝑧
Classical/Quantum/Other 3
![Page 4: Local («classical») correlations ≠ Quantum correlations · A.Tavakoli, MO.Renou, N.Gisin, N.Brunner (2017) 19 Correlations in star networks: from Bell inequalities to network](https://reader033.fdocuments.net/reader033/viewer/2022060715/607b1c8639c5ea701273cf68/html5/thumbnails/4.jpg)
z c
C
A B
Bell nonlocality
For a local hidden variable:
Characterize ℒ = 𝑃 ⊂ ℝ𝑞𝑝𝑟𝑞?4
![Page 5: Local («classical») correlations ≠ Quantum correlations · A.Tavakoli, MO.Renou, N.Gisin, N.Brunner (2017) 19 Correlations in star networks: from Bell inequalities to network](https://reader033.fdocuments.net/reader033/viewer/2022060715/607b1c8639c5ea701273cf68/html5/thumbnails/5.jpg)
Bell nonlocality
• ℒ is a polytope
• Vertices of ℒ are deterministic distributions
• 2 characterization of the polytope ℒ:
o Enumerate all deterministic distributions
o Enumerate all facets
5
![Page 6: Local («classical») correlations ≠ Quantum correlations · A.Tavakoli, MO.Renou, N.Gisin, N.Brunner (2017) 19 Correlations in star networks: from Bell inequalities to network](https://reader033.fdocuments.net/reader033/viewer/2022060715/607b1c8639c5ea701273cf68/html5/thumbnails/6.jpg)
Hyperplane 𝑆 ∈ ℝ𝑞𝑝𝑟𝑞 , 𝑆𝑘 ∈ ℝrepresents a Bell inequality
Bell nonlocality
Facets:
𝑆 ∙ 𝑃 =
𝑎𝑏𝑐𝑥𝑦𝑧
𝑠𝑥𝑦𝑧𝑎𝑏𝑐𝑝 𝑎𝑏𝑐 𝑥𝑦𝑧 ≤ 𝑆𝑘 , ∀𝑃 ∈ ℒ
6
![Page 7: Local («classical») correlations ≠ Quantum correlations · A.Tavakoli, MO.Renou, N.Gisin, N.Brunner (2017) 19 Correlations in star networks: from Bell inequalities to network](https://reader033.fdocuments.net/reader033/viewer/2022060715/607b1c8639c5ea701273cf68/html5/thumbnails/7.jpg)
Bell nonlocality
• ℒ is characterized by Bell inequalities, which are
« easily » enumerable.
• Starting point to find quantum violations
z c
C
A B
7
![Page 8: Local («classical») correlations ≠ Quantum correlations · A.Tavakoli, MO.Renou, N.Gisin, N.Brunner (2017) 19 Correlations in star networks: from Bell inequalities to network](https://reader033.fdocuments.net/reader033/viewer/2022060715/607b1c8639c5ea701273cf68/html5/thumbnails/8.jpg)
Bell nonlocality
A B 𝐵𝐴
𝒂 = ±𝟏 𝒃 = ±𝟏
*
𝐱 = 𝟏, 𝟐 𝒚 = 𝟏, 𝟐 𝝍−
8
A quantum Non-Local experiment
𝑃 ∉ ℒ, 𝑃 ∈ 𝒬:
The CHSH experiment
![Page 9: Local («classical») correlations ≠ Quantum correlations · A.Tavakoli, MO.Renou, N.Gisin, N.Brunner (2017) 19 Correlations in star networks: from Bell inequalities to network](https://reader033.fdocuments.net/reader033/viewer/2022060715/607b1c8639c5ea701273cf68/html5/thumbnails/9.jpg)
𝑃 ∈ ℒ
𝑃 ∈ 𝒬
𝑃 ∈ 𝒩ℒ
𝑃 ∈ 𝒩𝒬
Generalisation to Network-Locality
Independent sources → non convex problem
9
![Page 10: Local («classical») correlations ≠ Quantum correlations · A.Tavakoli, MO.Renou, N.Gisin, N.Brunner (2017) 19 Correlations in star networks: from Bell inequalities to network](https://reader033.fdocuments.net/reader033/viewer/2022060715/607b1c8639c5ea701273cf68/html5/thumbnails/10.jpg)
Some violations from Bell Nonlocality:
Network-Locality
CHSH violation
𝐵 𝐶
𝒄 = 𝟎, 𝟏
𝐴
𝒂 = 𝟎, 𝟏 𝒃 = 𝟎, 𝟏
𝝁
* *
𝐱 = 𝟎, 𝟏 𝒚 = 𝟎, 𝟏
𝝍−
10Not genuine Network-Locality violation!
![Page 11: Local («classical») correlations ≠ Quantum correlations · A.Tavakoli, MO.Renou, N.Gisin, N.Brunner (2017) 19 Correlations in star networks: from Bell inequalities to network](https://reader033.fdocuments.net/reader033/viewer/2022060715/607b1c8639c5ea701273cf68/html5/thumbnails/11.jpg)
Some violations from Bell Nonlocality:
𝐵 𝑌
y= 𝟎, 𝟏
𝐴
𝒂 = 𝟎, 𝟏 𝒃 = 𝟎, 𝟏
ϒ
* *𝑋
x= 𝟎, 𝟏*χ
Network-Locality
CHSH violation with input χ , ϒ
Answer x=χAnswer y=χ
𝝍−
11Not genuine Network-Locality violation!
![Page 12: Local («classical») correlations ≠ Quantum correlations · A.Tavakoli, MO.Renou, N.Gisin, N.Brunner (2017) 19 Correlations in star networks: from Bell inequalities to network](https://reader033.fdocuments.net/reader033/viewer/2022060715/607b1c8639c5ea701273cf68/html5/thumbnails/12.jpg)
• Bell-Nonlocality VS Network-Locality
• Bilocality & Extensions
• Triangle scenario
12
![Page 13: Local («classical») correlations ≠ Quantum correlations · A.Tavakoli, MO.Renou, N.Gisin, N.Brunner (2017) 19 Correlations in star networks: from Bell inequalities to network](https://reader033.fdocuments.net/reader033/viewer/2022060715/607b1c8639c5ea701273cf68/html5/thumbnails/13.jpg)
• Bell-Nonlocality VS Network-Locality
• Bilocality & Extensions
• Triangle scenario
13
![Page 14: Local («classical») correlations ≠ Quantum correlations · A.Tavakoli, MO.Renou, N.Gisin, N.Brunner (2017) 19 Correlations in star networks: from Bell inequalities to network](https://reader033.fdocuments.net/reader033/viewer/2022060715/607b1c8639c5ea701273cf68/html5/thumbnails/14.jpg)
1st bilocality inequality
𝐵 𝐶𝐴
𝒂 = ±𝟏 𝒃 = ±𝟏
𝝀 𝝁
* *
𝐱 = 𝟏, 𝟐 𝒚 = 𝟏, 𝟐 𝒛 = 𝟏, 𝟐
𝐜 = ±𝟏
I1 =1
4𝐴1 + 𝐴2 𝐵1(𝐶1 + 𝐶2) 𝜆,𝜇
I2 =1
4𝐴1 − 𝐴2 𝐵2(𝐶1 − 𝐶2) 𝜆,𝜇
C.Branciard, N.Gisin, and S.Pironio,
Characterizing the Nonlocal Correlations Created via Entanglement Swapping, Phys. Rev. Lett.104,170401 (2010)
𝑰𝟏 + 𝑰𝟐 ≤ 𝟏
Correlators:
𝐴𝑥𝐵𝑦𝐶𝑧
Mean value of 𝑎𝑏𝑐 for input 𝑥𝑦𝑧
14
![Page 15: Local («classical») correlations ≠ Quantum correlations · A.Tavakoli, MO.Renou, N.Gisin, N.Brunner (2017) 19 Correlations in star networks: from Bell inequalities to network](https://reader033.fdocuments.net/reader033/viewer/2022060715/607b1c8639c5ea701273cf68/html5/thumbnails/15.jpg)
CHSH
𝐵𝐴
𝒂 = ±𝟏 𝒃 = ±𝟏
𝝀
*
𝐱 = 𝟏, 𝟐 𝒚 = 𝟏, 𝟐
𝑆 = 𝐴1𝐵1 + 𝐴2𝐵1 + 𝐴1𝐵2 − 𝐴2𝐵2
Let: 𝐴1 = 𝐴1 + 𝐴2 𝐴2 = 𝐴1 − 𝐴2
Then:
𝑆 = 𝐴1𝐵1 + 𝐴2𝐵2
≤ 𝐴1𝐵1 + 𝐴2𝐵2
≤ 𝐴1 + 𝐴2 ≤ 2
𝐴1 + 𝐴2 ≤ 2
(Triang. Ineq.)
15
![Page 16: Local («classical») correlations ≠ Quantum correlations · A.Tavakoli, MO.Renou, N.Gisin, N.Brunner (2017) 19 Correlations in star networks: from Bell inequalities to network](https://reader033.fdocuments.net/reader033/viewer/2022060715/607b1c8639c5ea701273cf68/html5/thumbnails/16.jpg)
𝐵 𝐶𝐴
𝒂 = ±𝟏 𝒃 = ±𝟏
𝝀 𝝁
* *
𝐱 = 𝟏, 𝟐 𝒚 = 𝟏, 𝟐 𝒛 = 𝟏, 𝟐
𝐜 = ±𝟏
• Let 𝐼𝑖 =1
4 𝐴𝑖𝐵𝑖 𝐶𝑖 :
𝐼𝑖 ≤1
4| 𝐴𝑖|| 𝐶𝑖| =
1
4| 𝐴𝑖| | 𝐶𝑖|
• Then:
𝑆 = |𝐼1| + |𝐼2| ≤1
4| 𝐴1| | 𝐶1| + | 𝐴2| | 𝐶2|
≤1
2 𝐴1 + | 𝐴2| 𝐶1 + | 𝐶2|
≤ 1
(Triang. Ineq.)
(C.S. Ineq.)
1st bilocality inequality
16
![Page 17: Local («classical») correlations ≠ Quantum correlations · A.Tavakoli, MO.Renou, N.Gisin, N.Brunner (2017) 19 Correlations in star networks: from Bell inequalities to network](https://reader033.fdocuments.net/reader033/viewer/2022060715/607b1c8639c5ea701273cf68/html5/thumbnails/17.jpg)
1st bilocality inequalities
𝑰𝟏 + 𝑰𝟐 ≤ 𝟏
17
1st Bilocality inequality
Bilocality set
𝒩ℒ
Biquantum
set 𝒩𝒬=
Local set ℒ
C.Branciard, D.Rosset, N.Gisin, S.Pironio (2012),
Bilocal versus non-bilocal correlations in entanglement swapping experiments, Phys. Rev. A 85, 032119
![Page 18: Local («classical») correlations ≠ Quantum correlations · A.Tavakoli, MO.Renou, N.Gisin, N.Brunner (2017) 19 Correlations in star networks: from Bell inequalities to network](https://reader033.fdocuments.net/reader033/viewer/2022060715/607b1c8639c5ea701273cf68/html5/thumbnails/18.jpg)
1st bilocality inequalities
• Partial characterization
of 𝒩ℒ
• Tight
• Quantum violations
• Bilocal set: nonconvex
𝑰𝟏 + 𝑰𝟐 ≤ 𝟏
C.Branciard, D.Rosset, N.Gisin, S.Pironio (2012),
Bilocal versus non-bilocal correlations in entanglement swapping experiments, Phys. Rev. A 85, 032119
18
Bilocality set
𝒩ℒ
Biquantum
set 𝒩𝒬=
Local set ℒ
1st Bilocality inequality
![Page 19: Local («classical») correlations ≠ Quantum correlations · A.Tavakoli, MO.Renou, N.Gisin, N.Brunner (2017) 19 Correlations in star networks: from Bell inequalities to network](https://reader033.fdocuments.net/reader033/viewer/2022060715/607b1c8639c5ea701273cf68/html5/thumbnails/19.jpg)
1st bilocality inequality
Tight classical bound
obtained with deterministic
strategies for Bob
𝐵 𝐶𝐴
𝒂 = ±𝟏 𝒃 = ±𝟏
𝝀 𝝁
* *
𝐱 = 𝟏, 𝟐 𝒚 = 𝟏, 𝟐 𝒛 = 𝟏, 𝟐
𝐜 = ±𝟏
19A.Tavakoli, MO.Renou, N.Gisin, N.Brunner (2017)
Correlations in star networks: from Bell inequalities to network inequalities arXiv:1702.0386
Bilocality set
𝒩ℒ
Biquantum
set 𝒩𝒬=
Local set ℒ
1st Bilocality inequality
![Page 20: Local («classical») correlations ≠ Quantum correlations · A.Tavakoli, MO.Renou, N.Gisin, N.Brunner (2017) 19 Correlations in star networks: from Bell inequalities to network](https://reader033.fdocuments.net/reader033/viewer/2022060715/607b1c8639c5ea701273cf68/html5/thumbnails/20.jpg)
2nd bilocality inequality
𝐵 𝐶𝐴
𝒂 = ±𝟏 𝒃 = ±𝟏
𝝀 𝝁
* *
𝐱 = 𝟏, 𝟐 𝒚 = 𝟏, 𝟐 𝒛 = 𝟏, 𝟐
𝐜 = ±𝟏
I1 =1
4𝐴1 + 𝐴2 𝐵1(𝐶1 + 𝐶2) 𝜆,𝜇
I2 =1
4𝐴1 − 𝐴2 𝐵2(𝐶1 − 𝐶2) 𝜆,𝜇
𝐵 𝐶𝐴
𝒂 = ±𝟏 𝒃𝟏 = ±𝟏𝒃𝟐 = ±𝟏
𝝀 𝝁
* *
𝐱 = 𝟏, 𝟐 𝒛 = 𝟏, 𝟐
𝐜 = ±𝟏
C.Branciard, N.Gisin, and S.Pironio, (2010)
Characterizing the Nonlocal Correlations Created via Entanglement Swapping, Phys. Rev. Lett.104,170401
𝑰𝟏 + 𝑰𝟐 ≤ 𝟏
Correlators:
𝐴𝑥𝐵𝑦𝐶𝑧
Mean value of 𝑎𝑏𝑦𝑐 for input 𝑥𝑧
20
![Page 21: Local («classical») correlations ≠ Quantum correlations · A.Tavakoli, MO.Renou, N.Gisin, N.Brunner (2017) 19 Correlations in star networks: from Bell inequalities to network](https://reader033.fdocuments.net/reader033/viewer/2022060715/607b1c8639c5ea701273cf68/html5/thumbnails/21.jpg)
2nd bilocality inequality
𝐵 𝐶𝐴
𝒂 = ±𝟏 𝒃𝟏 = ±𝟏𝒃𝟐 = ±𝟏
* *
𝐱 = 𝟎, 𝟏 𝒛 = 𝟎, 𝟏
𝐜 = ±𝟏
• 𝜌𝑉 = 𝑉 𝜓− |𝜓− + (1 − 𝑉)𝐼𝑑
4
• 𝜌𝑉 violates CHSH iff 𝑉 >1
2
• If B does a Bell State Measurement : AC share 𝜌𝑉2
• Bilocality inequality is violated iff 𝑉2 >1
2
𝜌𝑉 𝜌𝑉
21
![Page 22: Local («classical») correlations ≠ Quantum correlations · A.Tavakoli, MO.Renou, N.Gisin, N.Brunner (2017) 19 Correlations in star networks: from Bell inequalities to network](https://reader033.fdocuments.net/reader033/viewer/2022060715/607b1c8639c5ea701273cf68/html5/thumbnails/22.jpg)
2nd bilocality inequality
𝐵 𝐶𝐴
𝒂 = ±𝟏 𝒃 = ±𝟏
𝝀 𝝁
* *
𝐱 = 𝟎, 𝟏 𝒛 = 𝟎, 𝟏
𝐜 = ±𝟏
Strong connections with CHSH violation:
• Violated by all pairs of pure entangled states
• With a BSM for Bob:
𝑆𝑚𝑎𝑥 ≤ 𝑆𝐴𝐵𝐶𝑚𝑎𝑥 𝑆𝐵𝐶
𝑚𝑎𝑥
𝜌 violates CHSH ↔ 𝜌⊗ 𝜌 violates biloc. ineq.
F.Andreoli, G.Carvacho, L.Santodonato, R.Chaves, F.Sciarrino
Maximal violation of n-locality inequalities in a star-shaped quantum network, arXiv:1702.08316
N.Gisin, Q.Mei, A.Tavakoli, MO.Renou, N.Brunner (2017)
All entangled pure quantum states violate the bilocality inequality arXiv:1702.00333
22
CHSHBilocality
With equality if
𝜌𝐴𝐵 = 𝜌𝐵𝐶
![Page 23: Local («classical») correlations ≠ Quantum correlations · A.Tavakoli, MO.Renou, N.Gisin, N.Brunner (2017) 19 Correlations in star networks: from Bell inequalities to network](https://reader033.fdocuments.net/reader033/viewer/2022060715/607b1c8639c5ea701273cf68/html5/thumbnails/23.jpg)
Extension: Star Network
Generalizable to any star network with binary output:
• With 𝐴1, 𝐴2, … → 𝐴1, 𝐴2, … ; 𝐵1, 𝐵2, … → 𝐵1, 𝐵2, … ;…
• And 𝐼𝑖 = 𝐴𝑖 𝐵𝑖 𝐶𝑖 …𝑀𝑖
𝑀
𝐴
𝐶
*
𝐵
𝒂 = 𝟎, 𝟏𝒃 = 𝟎, 𝟏
𝒄 = 𝟎, 𝟏
𝒐
𝝀𝝁
𝝂
*
*
𝒙𝒚
𝒛
𝒕
𝒊
𝑰𝒊𝟏/𝑵 ≤ 𝑪
23A.Tavakoli, MO.Renou, N.Gisin, N.Brunner (2017)
Correlations in star networks: from Bell inequalities to network inequalities arXiv:1702.0386
![Page 24: Local («classical») correlations ≠ Quantum correlations · A.Tavakoli, MO.Renou, N.Gisin, N.Brunner (2017) 19 Correlations in star networks: from Bell inequalities to network](https://reader033.fdocuments.net/reader033/viewer/2022060715/607b1c8639c5ea701273cf68/html5/thumbnails/24.jpg)
Extension
24
• For any correlator Bell inequality about network in terms of the 𝐴𝑥1
1 …𝐴𝑥𝑀𝑀
• Using the transformation
• Construct a new Bell inequality with terms 𝐴𝑥11 …𝐴𝑥𝑀
𝑀 𝐴𝑖𝑀+1
• Proof of CHSH, go from CHSH to Bilocality Inequality, …
D.Rosset, C.Branciard, T.Barnea, G.Pütz, N.Brunner, N.Gisin
Nonlinear Bell Inequalities Tailored for Quantum Networks Phys. Rev. Lett. 116, 010403 (2016)
𝐴1𝑀+1 = 𝐴1
𝑀+1 + 𝐴1𝑀+1
𝐴2𝑀+1 = 𝐴1
𝑀+1 − 𝐴1𝑀+1
𝐴1𝑀+1
𝐴2𝑀+1
![Page 25: Local («classical») correlations ≠ Quantum correlations · A.Tavakoli, MO.Renou, N.Gisin, N.Brunner (2017) 19 Correlations in star networks: from Bell inequalities to network](https://reader033.fdocuments.net/reader033/viewer/2022060715/607b1c8639c5ea701273cf68/html5/thumbnails/25.jpg)
• Bell-Nonlocality VS Network-Locality
• Bilocality & Extensions
• Triangle scenario
25
![Page 26: Local («classical») correlations ≠ Quantum correlations · A.Tavakoli, MO.Renou, N.Gisin, N.Brunner (2017) 19 Correlations in star networks: from Bell inequalities to network](https://reader033.fdocuments.net/reader033/viewer/2022060715/607b1c8639c5ea701273cf68/html5/thumbnails/26.jpg)
Triangle scenario
𝐵𝐴
𝒂 𝒃
*
𝐶
𝜸
𝒄
𝜷 𝜶
• Triangle network
• No input
26
![Page 27: Local («classical») correlations ≠ Quantum correlations · A.Tavakoli, MO.Renou, N.Gisin, N.Brunner (2017) 19 Correlations in star networks: from Bell inequalities to network](https://reader033.fdocuments.net/reader033/viewer/2022060715/607b1c8639c5ea701273cf68/html5/thumbnails/27.jpg)
Triangle scenario, 𝒩𝒬
𝐵𝐴
𝒂 = 𝟎, 𝟏𝒙 = 𝟎, 𝟏
𝒃 = 𝟎, 𝟏𝒚 = 𝟎, 𝟏
*
𝐶
𝝍−
𝒙′ = 𝟎, 𝟏𝒚′ = 𝟎, 𝟏
𝑿 ∈ {𝟎, 𝟏} 𝒀 ∈ {𝟎, 𝟏}
𝑋 ∈ 0,1 random bit
𝑥 = 𝑋𝑥′ = 𝑋
Y ∈ 0,1 random bit
y = 𝑌𝑦′ = 𝑌
Standard CHSH
violation, input 𝑋, 𝑌,
output 𝑎, 𝑏
27T.Fritz, (2012)
Beyond Bell's Theorem: Correlation Scenarios, New J. Phys. 14 103001
Can it be in 𝒩ℒ?
![Page 28: Local («classical») correlations ≠ Quantum correlations · A.Tavakoli, MO.Renou, N.Gisin, N.Brunner (2017) 19 Correlations in star networks: from Bell inequalities to network](https://reader033.fdocuments.net/reader033/viewer/2022060715/607b1c8639c5ea701273cf68/html5/thumbnails/28.jpg)
Triangle scenario, 𝒩ℒ
𝐵𝐴 *
𝐶
𝝀
𝒂 = 𝟎, 𝟏𝒙 = 𝟎, 𝟏
𝒃 = 𝟎, 𝟏𝒚 = 𝟎, 𝟏
𝒙′ = 𝟎, 𝟏𝒚′ = 𝟎, 𝟏
𝑿 𝒀
If 𝑃 ∈ 𝒩ℒ:
• ∀run, 𝑥 = 𝑥′: 𝑥 = 𝑥′ = 𝑓 𝑋• ∀run, 𝑦 = 𝑦′: y = 𝑦′ = 𝑔(𝑌)• 𝑝(𝑎𝑏𝑥𝑦) violates CHSH
Cannot be
explained
classically!
𝑿 𝒀
𝒂 = 𝟎, 𝟏𝒙 = 𝑿 = 𝟎, 𝟏
𝒃 = 𝟎, 𝟏𝒚 = 𝒀 = 𝟎, 𝟏
𝒙′ = 𝑿 = 𝟎, 𝟏𝒚′ = 𝒀 = 𝟎, 𝟏
≡ 𝑋
≡ 𝑌
28T.Fritz, (2012)
Beyond Bell's Theorem: Correlation Scenarios, New J. Phys. 14 103001
![Page 29: Local («classical») correlations ≠ Quantum correlations · A.Tavakoli, MO.Renou, N.Gisin, N.Brunner (2017) 19 Correlations in star networks: from Bell inequalities to network](https://reader033.fdocuments.net/reader033/viewer/2022060715/607b1c8639c5ea701273cf68/html5/thumbnails/29.jpg)
Triangle scenario, 𝒩𝒬
𝐵𝐴
𝒂 = 𝟎, 𝟏𝒙 = 𝟎, 𝟏
𝒃 = 𝟎, 𝟏𝒚 = 𝟎, 𝟏
*
𝐶
𝝍−
𝒙′ = 𝟎, 𝟏𝒚′ = 𝟎, 𝟏
𝑿 ∈ {𝟎, 𝟏} 𝒀 ∈ {𝟎, 𝟏}
𝑋 ∈ 0,1 random bit
𝑥 = 𝑋𝑥′ = 𝑋
Y ∈ 0,1 random bit
y = 𝑌𝑦′ = 𝑌
Standard CHSH
violation, input 𝑋, 𝑌,
output 𝑎, 𝑏
29
• Need 4 outputs (to check that nobody lies about his input)
• Not genuine example of Network-Locality violation, uses Bell
Nonlocality
T.Fritz, (2012)
Beyond Bell's Theorem: Correlation Scenarios, New J. Phys. 14 103001
![Page 30: Local («classical») correlations ≠ Quantum correlations · A.Tavakoli, MO.Renou, N.Gisin, N.Brunner (2017) 19 Correlations in star networks: from Bell inequalities to network](https://reader033.fdocuments.net/reader033/viewer/2022060715/607b1c8639c5ea701273cf68/html5/thumbnails/30.jpg)
2 output triangle scenario
Characterization of
𝒩ℒ?𝒩ℒ ≠ 𝒩𝒬?
𝐵𝐴
𝒂(𝜷, 𝜸)= 𝟎, 𝟏
𝒃(𝜸, 𝜶)= 𝟎,𝟏
*
𝐶
𝜸 ∈ [𝟎, 𝟏]
𝒄(𝜶,𝜷)= 𝟎, 𝟏
𝜷 ∈ [𝟎, 𝟏] 𝜶 ∈ [𝟎, 𝟏]
2 questions:
30
w.l.o.g. :
𝜶,𝜷, 𝜸 uniformly random in [𝟎, 𝟏]
![Page 31: Local («classical») correlations ≠ Quantum correlations · A.Tavakoli, MO.Renou, N.Gisin, N.Brunner (2017) 19 Correlations in star networks: from Bell inequalities to network](https://reader033.fdocuments.net/reader033/viewer/2022060715/607b1c8639c5ea701273cf68/html5/thumbnails/31.jpg)
Strategies 𝑺
w.l.o.g. :
𝑺 ≡ deterministic 𝑎(𝛽, 𝛾), 𝑏(𝛾, 𝛼), 𝑐(𝛼, 𝛽)
𝑝 𝑎 𝑏 𝑐 = 𝑑𝛼 𝑑𝛽 𝑑𝛾 𝛿𝑎(𝛽,𝛾) 𝑎 𝛿𝑏(𝛾,𝛼)
𝑏 𝛿𝑐(𝛼,𝛽) 𝑐
𝐵𝐴
𝒂(𝜷, 𝜸)= 𝟎, 𝟏
𝒃(𝜸, 𝜶)= 𝟎,𝟏
*
𝐶
𝜸 ∈ [𝟎, 𝟏]
𝒄(𝜶,𝜷)= 𝟎, 𝟏
𝜷 ∈ [𝟎, 𝟏] 𝜶 ∈ [𝟎, 𝟏]
31
![Page 32: Local («classical») correlations ≠ Quantum correlations · A.Tavakoli, MO.Renou, N.Gisin, N.Brunner (2017) 19 Correlations in star networks: from Bell inequalities to network](https://reader033.fdocuments.net/reader033/viewer/2022060715/607b1c8639c5ea701273cf68/html5/thumbnails/32.jpg)
Strategies 𝑺
Any 𝑺: Given by a cube with a 0 or a 1 for each point of 3 faces
𝛼𝛽
𝛾
𝟎
𝟏
𝟎
𝟏 0
𝟏
0
𝟏
𝟎 1
𝟎
1
1
𝟎
𝟎
𝟏
𝟏
0
𝑀
𝛼𝛽𝛾
𝒄(𝜶,𝜷)
𝒃(𝜶, 𝜸)
𝒂(𝜷, 𝜸)
32
![Page 33: Local («classical») correlations ≠ Quantum correlations · A.Tavakoli, MO.Renou, N.Gisin, N.Brunner (2017) 19 Correlations in star networks: from Bell inequalities to network](https://reader033.fdocuments.net/reader033/viewer/2022060715/607b1c8639c5ea701273cf68/html5/thumbnails/33.jpg)
Applications
• 𝒩ℒ ⊂ 𝒩𝒬 ⊂ ℝ8
• 𝑃0: 𝑝 𝑎𝑏𝑐 =1
8is “central”
• Is there some direction
𝑃0 + 𝛿𝑃 ∈ 𝒩𝒬,∉ 𝒩ℒ?
Not possible in standard Bell Nonlocality
Not obvious in Network-Locality
No dimensional advantage in Quantum theory
33
![Page 34: Local («classical») correlations ≠ Quantum correlations · A.Tavakoli, MO.Renou, N.Gisin, N.Brunner (2017) 19 Correlations in star networks: from Bell inequalities to network](https://reader033.fdocuments.net/reader033/viewer/2022060715/607b1c8639c5ea701273cf68/html5/thumbnails/34.jpg)
Applications
𝛼𝛽
𝛾
𝟎𝟎
𝟎
𝟎
𝟎
𝟎
𝟏
𝟏
𝟏
𝟏
𝟏 𝟏
No dimensional advantage in Quantum theory
• Take 𝑺𝟎 strategy for 𝑃0
• Vary it: obtain 𝑃0 + 𝛿𝑃
• Show that any 𝑃0 + 𝛿𝑃can be obtained
This can be generalized to any network
𝟏
𝟎
𝟏𝟎
34MO.Renou et al., in preparation
![Page 35: Local («classical») correlations ≠ Quantum correlations · A.Tavakoli, MO.Renou, N.Gisin, N.Brunner (2017) 19 Correlations in star networks: from Bell inequalities to network](https://reader033.fdocuments.net/reader033/viewer/2022060715/607b1c8639c5ea701273cf68/html5/thumbnails/35.jpg)
Finite rank model
35
𝛼𝛽
𝛾
𝟎
𝟏
𝟎
𝟏 0
𝟏
0
𝟏
𝟎 1
𝟎
1
1
𝟎
𝟎
𝟏
𝟏
0
𝑀
𝛼𝛽𝛾
𝒄(𝜶,𝜷)
𝒃(𝜶, 𝜸)
𝒂(𝜷, 𝜸)
𝛼𝛽
𝛾𝟎𝟎
𝟎
𝟎
𝟎
1
1
1
1
1
1
1
𝟎 𝟎
𝟎 𝟎
𝟎
𝟎
𝟎
𝟎
𝟎
𝟎
𝟎
1
11
1
1
11
1
1
1
𝑢𝑖
𝑤𝑘
𝑣𝑗
𝑃 =
𝑖,𝑗,𝑘=1
8
𝑢𝑖𝑣𝑗𝑤𝑘 𝑃𝑖,𝑗,𝑘 ,
𝑃𝑖,𝑗,𝑘 deterministic
𝑃 = 𝑑𝛼𝑑𝛽𝑑𝛾𝑃𝛼,𝛽,𝛾 ,
𝑃𝛼,𝛽,𝛾 deterministic
![Page 36: Local («classical») correlations ≠ Quantum correlations · A.Tavakoli, MO.Renou, N.Gisin, N.Brunner (2017) 19 Correlations in star networks: from Bell inequalities to network](https://reader033.fdocuments.net/reader033/viewer/2022060715/607b1c8639c5ea701273cf68/html5/thumbnails/36.jpg)
Finite rank model
• Consider 𝑺 → 𝑃
• Fix source 𝛼 = 𝛼0:
We obtain a new strategy
𝑺𝜶𝟎 → 𝑃𝛼0
• 𝑃 = ∫ 𝑑𝛼0𝑃𝛼0
𝐵𝐴
𝒂(𝜷, 𝜸)= 𝟎, 𝟏
𝒃(𝜸, 𝜶)= 𝟎, 𝟏
*
𝐶
𝜸 ∈ [𝟎, 𝟏]
𝒄(𝜶,𝜷)= 𝟎, 𝟏
𝜷 ∈ [𝟎, 𝟏] 𝜶 ∈ [𝟎, 𝟏]
𝑺 → 𝑃
𝜶 = 𝜶𝟎
𝑺𝜶𝟎 → 𝑃𝛼0
36
![Page 37: Local («classical») correlations ≠ Quantum correlations · A.Tavakoli, MO.Renou, N.Gisin, N.Brunner (2017) 19 Correlations in star networks: from Bell inequalities to network](https://reader033.fdocuments.net/reader033/viewer/2022060715/607b1c8639c5ea701273cf68/html5/thumbnails/37.jpg)
Finite rank model
𝑃 = ∫ 𝑑𝛼0𝑃𝛼0
Carathéodory theorem:
If 𝑃 ∈ ℝ𝑑 in convex hull of A, A convex, then 𝑃 is the
convex combination of d points of A
𝑃 =
𝑖=1
8
𝑢𝑖 𝑃𝑖 ,
𝑃𝑖 has a strategy independent from 𝛼
D. Rosset, N. Gisin, and E. Wolfe,
All n-local set are semialgebraic, in preparation
37
![Page 38: Local («classical») correlations ≠ Quantum correlations · A.Tavakoli, MO.Renou, N.Gisin, N.Brunner (2017) 19 Correlations in star networks: from Bell inequalities to network](https://reader033.fdocuments.net/reader033/viewer/2022060715/607b1c8639c5ea701273cf68/html5/thumbnails/38.jpg)
Finite rank model
𝑃 =
𝑖,𝑗,𝑘=1
8
𝑢𝑖𝑣𝑗𝑤𝑘 𝑃𝑖,𝑗,𝑘 , 𝑃𝑖,𝑗,𝑘 deterministic
𝛼𝛽
𝛾𝟎𝟎
𝟎
𝟎
𝟎
1
1
1
1
1
1
1
𝟎 𝟎
𝟎 𝟎
𝟎
𝟎
𝟎
𝟎
𝟎
𝟎
𝟎
1
11
1
1
11
1
1
1
𝑢𝑖
𝑤𝑘
𝑣𝑗
38
![Page 39: Local («classical») correlations ≠ Quantum correlations · A.Tavakoli, MO.Renou, N.Gisin, N.Brunner (2017) 19 Correlations in star networks: from Bell inequalities to network](https://reader033.fdocuments.net/reader033/viewer/2022060715/607b1c8639c5ea701273cf68/html5/thumbnails/39.jpg)
Applications
• GHZ distribution [𝑝000 = 𝑝111 =1
2]
∉ 𝒩ℒ
• 𝜔 distribution [𝑝001 = 𝑝010 = 𝑝100 =1
3]
∉ 𝒩ℒ
𝛼𝛽
𝛾
0
𝟎𝟎
𝟎
39
𝟎 𝟎 𝟎 𝟎 𝟎
![Page 40: Local («classical») correlations ≠ Quantum correlations · A.Tavakoli, MO.Renou, N.Gisin, N.Brunner (2017) 19 Correlations in star networks: from Bell inequalities to network](https://reader033.fdocuments.net/reader033/viewer/2022060715/607b1c8639c5ea701273cf68/html5/thumbnails/40.jpg)
Applications
Characterization of 𝒩ℒ:
Given 𝑃, answer to "𝑃 ∈ 𝒩ℒ"?
Enumerate all 0/1 repartition,
find a 𝑢𝑖 , 𝑣𝑗 , 𝑤𝑘 distributions:
too hard!
𝛼𝛽
𝛾𝟎𝟎
𝟎
𝟎
𝟎
1
1
1
1
1
1
1
𝟎 𝟎
𝟎 𝟎
𝟎
𝟎
𝟎
𝟎
𝟎
𝟎
𝟎
1
11
1
1
11
1
1
1
𝑢𝑖
𝑤𝑘
𝑣𝑗
40
![Page 41: Local («classical») correlations ≠ Quantum correlations · A.Tavakoli, MO.Renou, N.Gisin, N.Brunner (2017) 19 Correlations in star networks: from Bell inequalities to network](https://reader033.fdocuments.net/reader033/viewer/2022060715/607b1c8639c5ea701273cf68/html5/thumbnails/41.jpg)
Applications
• Restricted problems:
‒ Given 𝑝000, Max(𝑝111)?
‒ Given 𝑝001, 𝑝010, Max(𝑝100)?
𝛼𝛽
𝛾𝟎𝟎
𝟎
𝟎
𝟎
1
1
1
1
1
1
1
𝟎 𝟎
𝟎 𝟎
𝟎
𝟎
𝟎
𝟎
𝟎
𝟎
𝟎
1
11
1
1
11
1
1
1
𝑢𝑖
𝑤𝑘
𝑣𝑗
Carathéodory theorem
Φ 𝑃 = 𝑝000, 𝑝111 has a rank 2 strategy.
Ψ 𝑃 = 𝑝001, 𝑝010, 𝑝100 has a rank 3 strategy.41
MO.Renou et al., in preparation
![Page 42: Local («classical») correlations ≠ Quantum correlations · A.Tavakoli, MO.Renou, N.Gisin, N.Brunner (2017) 19 Correlations in star networks: from Bell inequalities to network](https://reader033.fdocuments.net/reader033/viewer/2022060715/607b1c8639c5ea701273cf68/html5/thumbnails/42.jpg)
Applications
• LoomisWhitney inequality:
𝑝0002 ≤ 𝑝0
𝐴𝑝0𝐵𝑝0
𝐶
• Could not find violation (with
maximally entangled qubit)
• Only one joint probability
𝛼𝛽
𝛾
𝑝000
𝟎
𝟎
𝟎
𝑝0𝐴
𝑝0𝐵
𝑝0𝐶
42
![Page 43: Local («classical») correlations ≠ Quantum correlations · A.Tavakoli, MO.Renou, N.Gisin, N.Brunner (2017) 19 Correlations in star networks: from Bell inequalities to network](https://reader033.fdocuments.net/reader033/viewer/2022060715/607b1c8639c5ea701273cf68/html5/thumbnails/43.jpg)
Link to computer science
Finner inequalities:
𝑝00…0 ≤
𝑖
𝑝0𝐴𝑖
𝜈𝑖,
The 𝜈𝑖 depends on the network
structure
𝑨𝟏
𝟎, 𝟏 𝟎, 𝟏𝟎, 𝟏
𝟎, 𝟏
𝟎, 𝟏
𝟎, 𝟏
𝟎, 𝟏
𝑨𝟐
𝑨𝟒
𝑨𝟔
𝑨𝟑
𝑨𝟓
𝑨𝟕
43
![Page 44: Local («classical») correlations ≠ Quantum correlations · A.Tavakoli, MO.Renou, N.Gisin, N.Brunner (2017) 19 Correlations in star networks: from Bell inequalities to network](https://reader033.fdocuments.net/reader033/viewer/2022060715/607b1c8639c5ea701273cf68/html5/thumbnails/44.jpg)
Link to computer science
𝑨𝟏
𝟎, 𝟏 𝟎, 𝟏𝟎, 𝟏
𝟎, 𝟏
𝟎, 𝟏
𝟎, 𝟏
𝟎, 𝟏
𝑨𝟐
𝑨𝟒
𝑨𝟔
𝑨𝟑
𝑨𝟓
𝑨𝟕
Variable Graph (locality assumption)
44
Finner inequalities:
𝑝00…0 ≤
𝑖
𝑝0𝐴𝑖
𝜈𝑖
𝑨𝟏
𝟎, 𝟏 𝟎, 𝟏𝟎, 𝟏
𝟎, 𝟏
𝟎, 𝟏
𝟎, 𝟏
𝟎, 𝟏
𝑨𝟐
𝑨𝟒
𝑨𝟔
𝑨𝟑
𝑨𝟓
𝑨𝟕
Dependency Graph (causality assumption)
Analogue inequalities:
𝑝00…0 ≤
𝑖
𝑝0𝐴𝑖
𝜇𝑖
𝜇𝑖 ≤ 𝜈𝑖: Possible quantum violation only with a gap
MO.Renou et al., in preparation
![Page 45: Local («classical») correlations ≠ Quantum correlations · A.Tavakoli, MO.Renou, N.Gisin, N.Brunner (2017) 19 Correlations in star networks: from Bell inequalities to network](https://reader033.fdocuments.net/reader033/viewer/2022060715/607b1c8639c5ea701273cf68/html5/thumbnails/45.jpg)
Acknowledgments
45
Nicolas GisinGAP-Geneva
Armin TavakoliGAP-Geneva
Nicolas BrunnerGAP-Geneva
Denis RossetNational Cheng Kung University, Tainan, Taiwan
Yuyi WangDistributed Computing Group-ETH
![Page 46: Local («classical») correlations ≠ Quantum correlations · A.Tavakoli, MO.Renou, N.Gisin, N.Brunner (2017) 19 Correlations in star networks: from Bell inequalities to network](https://reader033.fdocuments.net/reader033/viewer/2022060715/607b1c8639c5ea701273cf68/html5/thumbnails/46.jpg)
To conclude
46
• Bell Nonlocality /
Network-Locality
• Find 𝒩ℒ : hard non-convex
problem.
• Some 𝒬 violation for no-loop
network
𝐵𝐴
𝒂 𝒃
*
𝐶
𝜸
𝒄
𝜷 𝜶
• Partial characterization of 𝒩ℒ.
Other technics (Inflation).
No “genuine” example of
violation for the triangle.