Questions tagged [epr-experiment]

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If I start with an EPR pair and evolve one qubit through a unitary operation, what's really happening?

Suppose I have the EPR pair (maximally entangled state) as $|\phi\rangle$ and I apply an arbitrary matrix $U_3$ on the first qubit. $$U_3 = \displaystyle \left[\begin{matrix}\cos{\left(\frac{\theta}{...
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How do we know that entangled entities can retain their connection and knowledge of their counterpart irrespective of the distance between them? [duplicate]

Read this somewhere that entangled entities that were born together and therefore share a wave-function according to quantum theory can fly apart--even across the width of the galaxy--and still retain ...
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Components of Stern-Gerlach Filter

Came across a discussion of the EPR paradox and Bell's inequality in a psychology text. I started looking deeper into the Stern-Gerlach type experiments employed in the EPR discussion and found this ...
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Did the original EPR really consider an entangled state?

Or did only the subsequent thought experiments (Bohm & Aharonov, Bell) that introduced spin examine entangled states? The wikipedia article titled 'EPR paradox' claims as much: 'The thought ...
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Why would the classical (local) correlation in Bell's experiment rule out the cosine of the angle?

This question expands on a specific detail of this previous question: Why would classical correlation in Bell's experiment be a linear function of angle? I would have commented on/answered that ...
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1answer
78 views

EPR related question

Suppose two entangled electrons are emitted from a source. After traveling a long distance in opposite directions, each electron passes through separate but otherwise identical double slits. Will both ...
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51 views

In quantum teleportation when exactly the original EPR pair stops being entangled?

In quantum teleportation Alice and Bob share a pair of entangled particles (EPR pair made of particles 2 and 3, for example). Alice has another particle (1) whose quantum state she wants to send to ...
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What (set of) angles are allowed between 3 detectors in the EPR experiment?

David Mermin's often cited popular example uses 60 degrees between 3 detectors which yielded what is said to be the maximum violation. Cosine 60 squared yields 25 percent which was below the ...
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3answers
183 views

Is the Bell's paper on the EPR paradox coherent?

I tried to read the Bell's paper on the EPR paradox but i rapidly stepped on difficulties : $$A(\vec{a}, \lambda) = \pm 1 ,\ B(\vec{b}, \lambda) = \pm 1 \tag{1}$$ So we identify $A$ with particle 1 ...
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1answer
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EPR Paradox clarification

Basically, the paradox works like this: Two entangled particles (A and B) are a light year apart. 1. Measure the X spin of A 2. Measure the Z spin of B You ...
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5answers
219 views

Shouldn't classical physics force us to assume that there is determinism on a quantum scale?

I'm not a physicist, I have read a lot about Bell's theorem and the Einstein/Bohr debates and I have the following question: Judging by only classical physics, it seems we live in a 100% ...
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2answers
44 views

How does EPR pair shows simultaneously two defined values?

In the paper "Can Quantum-Mechanical Description of Physical Reality Be Considered Complete ?", it implies that with an entangled state it is possible to know two physical quantities simultaneously. ...
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4answers
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Moon paradox 2.0

Can anyone help me with what goes wrong with the following Moon paradox thought experiment ? You all know the faster than light (FTL) Moon "paradox": send a beam to the moon through a "hand laser," ...
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How to obtain Hamiltonian parameters with EPR technique

I want to ask you how to obtain the parameters of the spin Hamiltonian of a system. I’m doing simulations with the EasySpin tool to obtain these parameters such as, J, the anisotropy factors D and E, ...
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0answers
28 views

EPR: How does measuring x_1 determine x_2 with certainty?

I am an undergraduate familiarizing myself with EPR for my upcoming bachelor's thesis, but this is probably pretty basic stuff for you out there. I am referring to the famous Einstein-Podolsky-Rosen ...
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2answers
90 views

What makes particles lose entanglement or do they ever lose it?

Once we generate a pair of entangled electrons or photons, will they ever lose their entanglement? If yes, then what causes them to lose entanglement? If measuring them causes them to lose ...
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2answers
44 views

What's the meaning of distant measuring?

this is the context: Einstein, Podolsky, and Rosen concluded that there are two possibilities in the case of the spinning particles. Either (a) there is some mysterious, nonlocal interaction that ...
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3answers
75 views

Does the EPR paradox assume that entangled particles leave each other's light cones, or not?

So I was reading this post by Ethan Siegel, which introduces a recent talk by Lee Smolin. In the article, Siegel outlines the EPR paradox (or something like it) and mentions that it is based on the ...
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1answer
76 views

Sending Information With Entangled Particles

I learned from my quantum mechanics course that if you measure a quantum state twice, two things can happen: 1) You take the second measurement just after the first on. In this case, the result will ...
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1answer
106 views

Reality, locality, and universality in the EPR paradox

Apologies if this has been asked before. I did some searching but didn't see it anywhere asked quite like this. Thanks in advance for any insights. Caveat: I am an organic chemist and thus ...
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2answers
105 views

Better Entanglement Explanation Required [duplicate]

It seems to me I have not read or understood a better explanation for quantum entanglement than Einstein's left and right glove explanation. If some Aspect (pun intended) of an entangled quantum ...
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2answers
99 views

Is the spin in quantum entanglement set at the moment the particles are separated, instead of when measured? [closed]

Is the spin in quantum entanglement set the moment the particles are separated, instead of transmitted instantaneously to its twin particle at the time of measurement? Wouldn't this make more sense ...
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1answer
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The non-locality of Quantum Mechanics

I often heard physicists mentioning the EPR paradox or the quantum entanglement when talking about the non-locality of quantum mechanics, but wasn't quantum mechanics already non-local from the ...
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1answer
28 views

question regarding wikipedia page on pulsed electron paramagnetic resonance

Here, under the subtitle 'principle,' it describes what happens when you have a static magnetic field along the z axis, $ B_0 \hat{z}$ and microwave field parallel to the $x$ axis, $ B_1 \hat{x}$. I ...
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3answers
139 views

Quantum entanglement, how do we know there was no spin? [duplicate]

Im not a scientist, so go easy on the explanation! As I understand it we can create two entangled particles. The entangled particles have a spin property which is opposing. When we measure one of the ...
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1answer
68 views

When does the wave function collapse in the EPR paradox experiment? Shouldn't this depend on the reference frame?

Suppose you have two entangled particles. Particle A, and Particle B. If the spin of particle A is up, then the spin of particle B must be down and vice versa. Now suppose you measure the spin of A ...
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1answer
80 views

Distinguish Definitions: Realism Scientific, Realism, and realistic

I was readying about study about bell's theorem, where I had the question about some definitions. Here's some of my summaries: Scientific Realism: (https://en.wikipedia.org/wiki/Scientific_realism#...
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193 views

How are joint measurements of quantum states realized experimentally?

I have a question regarding the experimental implementation of joint measurements of quantum states. While I understand for example the teleportation protocol using Bell states, something that still ...
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49 views

What's the invariance quantity under EPR and Bell's inequality?

I was reading and writing a study report about EPR and Bell's inequality. As the hidden variable and local realism was proven to be "false", and from many posts in physics exchange websites such as ...
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1answer
125 views

Are properties such as locality and realism properties of all theories, some theories, or interpretations of theories?

I have a strong intuitive feeling, based for example on the Bothe-Geiger experiment, that quantum mechanics is nonlocal. But intelligent people who have thought about these things make claims such as ...
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1answer
259 views

From locality to deterministic hidden variables

According to this link here Bell said: "My own first paper on this subject ... starts with a summary of the EPR argument from locality to deterministic hidden variables. But the commentators have ...
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68 views

EPR experiment with photons

In textbooks, the EPR problem and Bell's Inequality are dealt with for particles. However, when it comes to experimental verification, photons are used. The formula for the expectation value for ...
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1answer
211 views

Completeness of quantum mechanics and the EPR paradox

I am reading through the EPR paper and follow most of it. The authors argue that either QM must be incomplete (let's call this statement A), or incompatible observables can not have simultaneous ...
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2answers
102 views

EPR-Bohm paradox and Robertson uncertainty relation [closed]

Consider Bohm's version of the EPR paradox, where spin-1/2 are used. The bipartite system is in the state $$ \vert \Psi\rangle = \dfrac{1}{\sqrt{2}} \left( \vert \uparrow_x \rangle_A \vert \...
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60 views

What confidence level and margin of error are implicit in the statement the probabilistic predictions of quantum mechanics have been firmly confirmed?

This can be formulated as a problem of hypothesis testing, or sampling, in a statistical framework. For a confidence level of 0.95, and an error not exceeding 0.005, you would need a sample size ...
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95 views

Is there any basis in stating there are different levels of 'locality' or 'reality', within physics or physical theories?

EPR’s reality criterion and quantum realism has this paragraph (the paper has 0 citations, and I'm personally happy to call this metaphysics, but still!): A popular interpretation of Bell’s theorem ...
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196 views

Is it possible to know the efficiency of a particle detector without assuming the truth of Theory (e.g.,, Quantum Theory)

I reorganized the question to clarify exactly what it is that I'm asking. Suppose an experiment is performed where a particle detector records 50 particles per second, on average. Absent any other ...
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1answer
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How to understand the claim that ''positions'' of entangled particles are correlated? [closed]

Are both particles detected in the exact same spot of the detector? Something else?
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Understanding the classical expectation side of EPR/Bell inequalities

I like building educational models[1], and I’m collecting ideas for a quantum physics based one. I’m wanting to make sure I’ve got my head around the classical side of the Bell inequalities, ...
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1answer
365 views

Bell's theorem and how it solves the EPR paradox

Could someone explain to me how Bell's theorem solves the EPR paradox and 'spooky action at a distance'? From what I understand, when measuring a state, say spin up in the x direction, the wave ...
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1answer
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Since photons do not experience time (nor distance in that case), why did Einstein think it was “spooky action at a distance”? [closed]

A photon travels at c, so it experiences no time or distance. I imagine from the photon's perspective, it's rather just like a simple dot on some kind of 4D manifold. So it begs the question of why ...
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1answer
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QM explanation on entanglement for spin and the original EPR experiment

I have read this: http://en.wikipedia.org/wiki/EPR_paradox#Mathematical_formulation and this: How does non-commutativity lead to uncertainty? But it does not give me a specific explanation on the ...
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Quantum field theory version of EPR paradox

I've always been wondered that people speaking of EPR paradox formulate it only in terms of non-relativistic quantum mechanics and not quantum field theory which being a relativist generalisation of ...
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1answer
99 views

What causes the universe to manifest a given value upon measurement in super-deterministic theory? [closed]

Bell's inequalities show that we have to give up freedom or local realism. If we give up freedom, we have super-determinism, if we give up local realism, we have free-will. In super-deterministic ...
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409 views

Shouldn't local realism imply the superdeterminism?

I see that Bell has ruled out Einstein's local realism but not supredeterminism. I see that Bell has confessed that superdeterminism kills his inequality. You cannot apply Bell's inequality if ...
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50 views

Hidden character in EPR paradox [duplicate]

I am a beginner in Quantum Mechanics so i am pretty new to the EPR paradox although i have heard about it a long time ago but finally studying in detail. And came across a doubt: Why the hidden ...
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2answers
210 views

How is locality preserved in quantum mechanics?

I was reading this post: http://motls.blogspot.com/2015/06/locality-nonlocality-and-anti-quantum.html Specifically here: "There is no nonlocality. There is no action at a distance. There is no doubt ...
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Has Jaynes' argument for quantum mechanics as a possible theory of inference been debunked?

To my understanding, there is currently no scientific consensus on which interpretation of quantum physics is the correct one, if any. The most famous one, perhaps for historical reasons, is the ...
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Has Jaynes's argument against Bell's theorem been debunked?

As a student of theoretical physics I'm well acquainted with the multitude of crackpot ideas attempting to circumvent Bell's theorem regarding local hidden variable theories in quantum physics. ...
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1answer
159 views

EPR experiment with identical particles

This question is an extension of a question I asked earlier about the possibility of measuring the energy of just one particle in a system of many identical particles, which can be found here. One ...