# What is Chsh: Definition and 20 Discussions

chsh (an abbreviation of "change shell") is a command on Unix-like operating systems that is used to change a login shell. Users can either supply the pathname of the shell that they wish to change to on the command line, or supply no arguments, in which case chsh allows the user to change the shell interactively.

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1. ### A The experiment for testing the CHSH inequalities

I want to understand how an experiment is carried out to test violations of the CHSH inequalities. I have read Wikipedia and one popular book on quantum mechanics. The Wikipedia article is too short and incomprehensible to me; in addition, the description from Wikipedia and from the book is...
2. ### I CHSH inequality : renaming and absolute values

In some derivations of the CHSH inequality, https://en.m.wikipedia.org/wiki/CHSH_inequality, the following arises : $$CHS=\int A(a,l1)B(b,l1)dl1-\int A(a,l2)B(b',l2)dl2+\int A(a',l3)B(b,l3)dl3+\int A(a',l4)B(b',l4)dl4\\ =\int A(a,l)B(b,l)dl1-A(a,l)B(b',l)+A(a',l)B(b,l)+A(a',l)B(b',l)dl$$ 1)...
3. ### I Can Exact Joint Probability Distributions Predict Violations in CHSH Tests?

I've spent some time setting up my simulation of a photonic EPR experiment and came up with an exact joint probability distribution for the outcomes ##P_{xy}(\alpha,\beta)##. To calculate the CHSH number we need the probability of a coincidence for each of the possible settings which becomes a...
4. ### I Computing CHSH violation bound

It seems that the upper bound of the CHSH inequality is ##2\sqrt{2}## How is it analytically derived?
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### I Difference between CHSH and Bell inequalities

Bell's Inequality, P(a,b)-P(a,d)+P(c,b)+P(c,d) is calculated as: S = a*b - a*d + c*b + c*d <= 2. It is valid for all values of a, b, c and d between -1 and +1 It is also valid for counts, a=a's counts/total counts of a,b,c &d. b, c,and d are derived similarly. Negative counts are not allowed...
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### I Bell's Inequality is only valid for non-negative numbers

The Bell Inequality tests are only valid for positive numbers, which is reasonable because counts and probabilities cannot be negative. CHSH generates a negative number, which means CHSH experiments are invalid. Bell's Inequality can be violated by having a negative value. For example...
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### B How does a Bell State lead to a probability in the CHSH game

Hi, I am a student in the Netherlands, and I'll be attending university next year. However, I am doing some form of research on Quantum Computing with another student for our so-called "profielwerkstuk" but my understanding of Quantum Physics and math is sometimes not at the level that is...
8. ### Adding expectation values to a CHSH animation

An animation of the CHSH experiment to generate correlated photons is at: http://www.animatedphysics.com/games/photon_longdistance_chsh.htm @georgir has a program to show the calculations using the formula for photon detection return Math.random() < (Math.cos(r(p-a)*2)+1)/2; yields the...
9. ### Difference between Bell and CHSH?

Is it correct to say that Chsh does not need an average but as soon as AB-AB'+A'B+A'B' is 4, 0 or -4 it means it is nonlocal ?
10. ### Numerical violation of CHSH?

In the hidden variable model for CHSH, I computed the probabilities for the CHSH operators to have results -4,-2,0,2,4, then the average S. Using a computer program, I could find the minimum of that function, obtaining S>2 : #include<stdio.h> #include<math.h> double PI=4.0*atan(1.0)...
11. ### Measurement operator for Chsh experiment

The experiment is described at p26 of http://arxiv.org/abs/quant-ph/0402001 In this experiment we see that we sum measurement results and not measure the sum. Is then the quantum measurement operator not : S=A\otimes B\otimes\mathbb{1_{64}}-\mathbb{1_{4}}\otimes A\otimes...
12. ### Calculating measurement probabilities for the CHSH game

Hi All, First, the context for this question can be found in Wilde's Quantum Shannon Theory text on the arXiv, specifically the section starting at the bottom of page 98, entitled "Entanglement in the CHSH Game". My particular question relates to Exercise 3.5.11 on page 100 of the same...
13. ### Variation on Quantum cross covariance and CHSH

I tried another approach to the problem of covariance like in Bell's theorem :from the definition ##Cov(A,B)=\langle\Psi|A\otimes B|\Psi\rangle-\langle\Psi|A\otimes 1|\Psi\rangle\langle\Psi|1\otimes B|\Psi\rangle## (##A=diag(1,-1)=B##) we can see that this 'average' is in fact a quadratic form...
14. ### Derivation of the CHSH inequality

Bell's 1971 derivation The following is based on page 37 of Bell's Speakable and Unspeakable (Bell, 1971), the main change being to use the symbol ‘E’ instead of ‘P’ for the expected value of the quantum correlation. This avoids any implication that the quantum correlation is itself a...
15. ### The triangle inequality in CHSH, where is the triangle?

http://en.wikipedia.org/wiki/CHSH_inequality#Bell.27s_1971_derivation The last step of the CHSH inequality derivation is to apply the triangle inequality. I see there are relative polarization angles, but I don't see any sides have defined length to make up a triangle. Where is the triangle?
16. ### Help me understand a simplified CHSH (Bell's) experiment

Hi all. At first, I'm not a physicist, I'm a programmer, and English is not my native language, that's why something in my text might sound not quite right. While researching various quantum entanglement experiments (just a hobby) I found one great article written by supposedly...
17. ### CHSH and the triangle inequality

Hello everybody, I've been trying to understand the CHSH proof as it is listed on Wikipedia: http://en.wikipedia.org/wiki/CHSH_inequality I got to this without any problem: E(a, b) - E(a, b^\prime) = \int \underline {A}(a, \lambda)\underline {B}(b, \lambda)[1 \pm \underline {A}(a^\prime...
18. ### Violating of CHSH inequality

Obviously a violation of the CHSH inequality means that local realistic theories are untenable. If we sent two entangled photons towards detectors (far enough away that for information to travel, you'd require it to go faster than light). One reaches a detector before the other, so...
19. ### Relativistic corrections to CHSH vs. Preferred frame

OK, here is an interesting assertion I haven't seen before. Thought I would see what some of the folks here think. The paper is: Quantum Preferred Frame: Does It Really Exist? by J. Rembielinski, K. A. Smolinski (2009) Abstract: "The idea of the preferred frame as a remedy for...
20. ### How Can Bell's Inequality Be Transformed into the CHSH Inequality?

Homework Statement I need to get the CHSH inequality from Bell's inequality Homework Equations |C(a, b) - C(a, b')| + |C(a', b) - C(a', b')| <= 2 to -2 <= C(a, b) - C(a, b') + C(a', b) + C(a', b') <= 2 The Attempt at a Solution I know the CHSH allows for no correlation of...