Questions tagged [bells-inequality]
Bell's inequality is a no-go theorem contrasting crucial correlations of physical observables in QM to those of the world as described by classical mechanics, essentially local hidden variables theories serving as a viable "explanation" of QM: QM inevitably violates these inequalities, as observed. Further use for the CHSH inequality generalization.
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Why can't the universe have counterfactual definiteness, determinism, and locality? [closed]
As I understand it, strictly deterministic models imply correlations over arbitrarily long distances. So a model cannot be both deterministic and local. I understand that this is a result of Bell's ...
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Multi-partite Bell's inequality test
Many two-partite Bell's inequality test have been done by measuring the visibility of the interference pattern as you can see in the paper below:
https://journals.aps.org/prl/abstract/10.1103/...
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In what sense is Bell's inequality "probabilistic", while the GHZ experiment is "definite"?
I read the paper about the GHZ contradiction written by David Mermin and he said that Bell's inequality is probabilistic while GHZ experiment is definite.
Here is that paper:https://journals.aps.org/...
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How do proponents of superdeterminism explain the specific choice of values for the hidden variables that violates the Bell inequality?
I don't have a background in physics, but I have an amateur interest in quantum mechanics, and I recently found out about the notion of superdeterminism. From what I understand, superdeterminism ...
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Can a point in the quantum set of correlations violate more than one independent facet Bell inequality?
Usually, depictions of the quantum set of correlations and the local polytope look something like:
In this image it looks like non-local points belonging to the quantum set (in yellow) violate only ...
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Is there any minimalistic version of superdeterminism theory?
Superdeterminism is one wild conjecture which is an alternative to the standard quantum mechanical interpretation and preserves local realism
Superdeterminism seems to be too much of a stretch. If ...
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Is spooky action at a distance real or does hidden variables exist? What does it mean in context of free will? [closed]
I am complete amateur at this and research about physics is just a hobby for me. So with that in mind here is my problem:
I saw a few debates between physicists about spooky action at a distance vs ...
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Experimental Demonstration of Entanglement?
In many papers about entangled sources, they use an experimental setup like this one to demonstrate their entanglement:
The setup involves measuring coincidences at the detectors at various angles of ...
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Is the possible Bell's test loophole of entangled particles communicating at a non instantaneous but FTL speed addressed and eliminated? [closed]
TLDR:
There seems to be a loophole in Bell's test that is not addressed or eliminated before we can successfully conclude that it proves that the Universe is unreal and non local. The entangled ...
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Deriving probability in Bell's inequality
Measuring the spin with an arbitrary angle $\theta$ with respect to the plane xz we obtain the spin operator (multiplying Pauli matrices per the
projection $(\cos\theta,\sin\theta)$)
$$\hat{\mathrm{S}}...
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How can we be sure Bell's theorem disproves local realism when we are not sure whether the measuring apparatus is in some form of entanglement or not? [duplicate]
Bell's therorem seems to disprove localism because measuring, let's say spin of an entangled electron, seem to communicate the measurement to it's another pair instantaneously.
But isn't another thing ...
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Can you provide an example quantum system that violates Bell's inequality? [closed]
I am self-learning QM. I am reading this paper about Bell's theorem https://arxiv.org/pdf/1212.5214.pdf and having difficult to understand the quantum system example in the paper that violates Bell's ...
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Why does it make sense to add/subtract the results of measuring in 2 different bases in Bell's inequality when each observer only measures 1 property?
In the CHSH inequality, we construct an experiment whereby two observers each receive a particle and measure two given properties of their particles, for which the outcomes are ±1. We then consider ...
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Entanglement correlations 2 [duplicate]
About the alleged duplicates: " Quantum entanglement vs classical analogy" "Show quantum entanglement to a classical thinker" refer to black and white balls that would have a ...
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Understanding superdeterminism
I was reading about superdeterminism and it was a bit counter-intuitive. The idea of having a hidden variable on the measurement device is very rational. For example, if we emit light to a constrained ...
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Is a super-deterministic universe local or nonlocal? [closed]
Bell predicted predetermined (nonlocal) choice as the criteria for a super-deterministic universe.
...our belief that we are free to choose to do one experiment rather
than another, absolutely ...
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True Randomness/unpredictability in infinite quantum coin toss sequences?
In Comments on indeterminism and undecidability the abstract reads:
"In a recent paper 1, it has been claimed that the outcomes of a quantum coin toss which is idealized as an infinite binary ...
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Is the ER=EPR conjecture a loophole in Bell's theorem that would allow for local realism to hold?
Specifically, if it turned out the mechanism for quantum entanglement is that all particles are somehow connected to each other via wormholes (assuming that is what the conjecture actually says), it ...
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Does the Kochen–Specker theorem allow to show experimentally the trouble with hidden variable theories?
Kochen–Specker theorem is one of the 'no-go' theorems for hidden variables theories. Is it possible using Kochen–Specker theorem to show experimentally that hidden variables theories reproducing QM ...
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Could number-theoretic "statistical independence" results (e.g. Chowla's conjecture) be used to disprove superdeterminism?
I will admit I only have the most basic understanding of superdeterminism, from this PBSspacetime video, in particular at this link https://youtu.be/JnKzt6Xq-w4?t=584 (I have provided the relevant ...
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Have spin-correlation experiments been done on entangled particles other than photons?
I know that Bell experiments on spin correlations have been done with entangled photons, but have spin-correlation experiments ever been done on entangled particles other than photons?
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Is the Copenhagen interpretation local?
In Wikipedia's table of interpretations of quantum mechanics there is a column for "local dynamics" where under the Copenhagen interpretation states "yes[citation needed]". Should ...
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How does Bell's theorem disprove realism?
I am told that the the violation of Bell's inequalities prove that the universe cannot have local realism. That is to say, the universe cannot both be local and real.
I understand how Bell's theorem ...
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Bell's Original Paper - Local hidden variable theories correlations smaller than entanglement
I'm having trouble following Bell's derivation of equation 22 in his original paper. Particularly, how to go from
$$
| \overline{P} (\vec{a}, \vec{b}) - \overline{P}(\vec{a}, \vec{c}) | \leq 1 + \...
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Is degeneracy of eigenvalues required for the Kochen-Specker theorem?
I'm wondering why the operators for the Kochen-Specker theorem are 3-dimensional while they only produce two eigenvalues $\{0,1\}$. Is this degeneracy always needed regardless of the dimensionality of ...
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Quantum entanglement Bell's inequality and Nobel prize [closed]
Just your average layman here, wanting to understand the whole entanglement work for the Nobel prize.
Why can't the entangled pairs have a fixed spin that we don't know? How do experiments prove ...
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Toy example of superdeterminism using Rule 30
From what I understand of Bell's Theorem, it requires giving up local realism or embracing superdeterminism. I still haven't been able to understand why superdeterminism gets such a bad rap, so I've ...
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How do we know the location of entangled particles after leaving the source so that we can set up our measurement devices?
Studying the Bell Inequality and was wondering how exactly experiments like Bell's are conducted. I understand the premise of the experiment to be that an entangled pair of photons or other quantum ...
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Are Bell's inequality and CHSH inequality the same?
Are Bell's inequality and CHSH inequality different? I tried to read about them and I understood that both disprove local hidden variable theory but I do not understand how they are different(if they ...
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Quantum Entaglement and EPR [closed]
I was studying the EPR Paradox and Bell's theorem . My question is how does this information travel between two entangled particles, has there been any research into this?
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Conditions necessary for experimental conflict with Bell's Theorem
In Aspect 2002 - Bell's Theorem, the Naive view of an Experimentalist, he suggests conditions necessary for coming up with situations/experiments that can conflict with Bell's inequality. I'm ...
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Is it possible to test if the entangled twin of a particle has already been measured or not? [duplicate]
Suppose a pair of entangled particles having opposite up/down spins are produced on Earth.
These two particles are then separated, one remaining on Earth, and the entangled pair being brought by ...
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Commutator of operators in relativistic quantum field theory
I am an undergrad student currently reading Bell Nonlocality review paper by Brunner et al. (2014). There is a part of the paper that I found weird. On page 425, on the set of quantum behaviours (see ...
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In the context of Bell nonlocality, is the space of behaviours a hypersphere?
I am currently reading Bell Nonlocality review paper by Brunner et al. (2014). On page 424,
A behaviour can be viewed as a point $\mathbf{p} \in \mathbb{R}^{\Delta^2 m^2}$ belonging to the ...
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In the Bell CHSH experiment, why are Alice and Bob not allowed to pre-arrage their measurements?
From Nielsen and Chuang, Chapter 2:
Imagine we perform the following experiment, illustrated in Figure 2.4. Charlie prepares
two particles. It doesn’t matter how he prepares the particles, just that ...
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How to find the uncertainty in an experiment where we only measure a single set of results?
I was reading about a Bell’s inequality experiment from the paper https://arxiv.org/abs/quant-ph/0205171.
In the paper it gives a set of recorded values:
I understand how they got the value for S, ...
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Quantum mechanics: does many-worlds interpretation remove nonlocality? Bell-type experiment
Trying to make sense of many-worlds interpretation and see if it removes nonlocality or solves other problems. It appears to me that branching is equivalent to collapse... so trying to see what I'm ...
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How are the different derivations of Bell's inequality related?
I wanted to ask about two different derivations for bell's inequality for the known CHSH inequality.
One derivation is the one bell originally used in 1971
this derivation is thoroughly written in ...
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Is it possible to derive Bell's inequalities without ever mentioning hidden variables?
In a discussion in another question, a user named @Claudiu showed me his own version of the derivation of CHSH inequality that does not need hidden variables (reproduced below). I can just wonder if ...
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Can we determine what the wavefunction (states) of a particle is before we decide which measurement to make?
If we are measuring spin-up or spin-down then we write the wavefunction (I think) as
$$ \require{physics} \psi = \tfrac{1}{\sqrt{2}} |{\uparrow}\rangle+\tfrac{1}{\sqrt{2}} |{\downarrow}\rangle $$
But ...
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What is an event-ready scheme (at-a-glance) in the context of Bell-type tests?
The abstract of Loophole-free Bell inequality violation using electron spins separated by 1.3 kilometres says
We use an event-ready scheme that enables the generation of robust entanglement between ...
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Can Einstein's hidden-variables idea explain a Bell-type experiment with only two measurement directions? [closed]
Can Einstein's hidden-variables idea explain a Bell-type experiment with only two measurement directions?
Let’s give Alice and Bob two choices – they can either measure their spin at 0 degrees or 180 ...
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Is this a correct example of a superdeterminism?
I'm trying to wrap my head around the recent 2022 nobel price and learned about the superdeterminism (https://en.wikipedia.org/wiki/Superdeterminism) loop hole in the now famous Aspect experiment (...
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Question about Bell's 1964 paper and its Illustration section [duplicate]
I have been trying to understand the maths behind the original paper on the EPR paradox, and I understand most of the details within it, in particular the main argument. However it is in the third ...
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Any Bell Experiments Showing Inequality Violations in Purely Classical Systems and What this Would Mean If So?
Are there any legitimate experiments/papers out there that have shown a violation of the Bell Inequalities in purely classical systems in which local realism couldn't sanely be called into question? I ...
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Is there a general version of Bell's inequality, like the general version of uncertainty principle?
By the general version of uncertainty principle, I mean the result involving general operators $A$ and $B$, which says that the products of standard deviations is equal to the sum of the expected ...
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How can a superdeterministic theory ever match Quantum Mechanic's predictions?
Superdeterminism says that we can observe violations from Bell's constraint for local hidden variable theories, if we assume the measurement choices are correlated, which they must be in a ...
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Are the inequalities from Bell's Theorem ever actually satisfied?
Following Griffiths's description from Introduction to Quantum Mechanics, Bell's original experiment was based on the EPR-Bohm experiment, where one considers the decay of a neutral pi meson into an ...
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Don't Bell experiments rule out local non-realism too? [duplicate]
Bell experiments rule out local realism (hidden variables). But it seems to me that it also rules out local non-realism (no hidden variables).
Local non-realism makes 2 claims;
Two distant events can'...
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Where did I go wrong with quantum photon polarization?
J Murray answered a previous question with a proof of Bell's Inequality, and a description of it applying to photon polarization.
I probably misunderstood the application to photons, so I want to get ...
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