# Tag Info

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Entanglement is a real property that can be shown by the violation of the Bell inequalities. How this is commonly done is that a pair of particles are created with entangled spin states in a configuration called Bell states. If entanglement is real, then measuring the state of one particle will give me definite knowledge of the state of the other particle. ...

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This problem has been pointed out historically in what is now universally abbreviated as the EPR paper, for which I'll simply refer you to an answer to a very similar question. This seemingly paradoxical effect has been observed experimentally. Some people insist the question of whether it is "real" is still unresolved. The main difficulty, however, is ...

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"Entanglement" is a term describing economically the quantum mechanical state of a system of particles. It is a short hand way of saying : these particles are described by the solution of the Schrodinger equation, with a wave function that can predict the probability of finding the individual particles in a specific (x,y,z) each with specific quantum ...

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They are entirely unrelated concepts. Two entangled particles are not "clones" of each other which magically do everything the same way; they merely have been put into a state which displays a strange statistical correlation when you "bring both parts back together." So for example a free neutron and an electron both have the same spin-1/2 structure; you ...

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Once two particles are entangled, they remain so at any distance, so long as you do nothing which would push them to lose coherence with each other. Entanglement is independent of distance. However, as a practical matter, it takes time to move the particles apart. Increasing distance increases how long it took to get them there. This means there's a ...

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A very good question. First of all, topological order strictly speaking is only defined for gapped states. But to some extent it can coexist with gapless degrees of freedom. A rather trivial example is just adding something gapless decoupled from the topological order (i.e. phonons). The example of the Kitaev model is quite different though, since the ...

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The problem is that entanglement doesn't mean that a measurement on the first particle determines the outcome of the second. Although this is often perpetuated, it's not the gist of entanglement. Entanglement is (mostly?) nonclassical correlations. Bipartite states are correlated, when the outcome of the measurement on one particle tells us something about ...

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$\newcommand{\HH}{\mathcal{H}}$As Martin says, entanglement is correlation rather than anything like "determining" the state of the other particle. We don't necessarily even need to talk about correlations, though, although they are one of the primary interesting features of entangled states. More precisely, your quote Quantum entanglement is a physical ...

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Suppose we have two Hilbert spaces $\mathcal{H}_A$ and $\mathcal{H}_B$. A quantum state on $\mathcal{H}_A$ is a normalized, positive trace-class operator $\rho\in\mathcal{S}_1(\mathcal{H}_A)$. If $\mathcal{H}_A$ is finite dimensinal (i.e. $\mathbb{C}^n$), then a quantum state is just a positive semi-definite matrix with unit trace on this Hilbert space. ...

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The answer is simple: measurement causes the wave-functions to collapse. It can be said that one of the fundamental properties that makes Quantum mechanics so strange is the idea of superposition, which is the property that if you have two physically valid descriptions of a state, then it is physically just as valid for a system to be in any linear ...

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Entanglement isn't about interaction or information transfer betweeen entangled particles. Consider spin-entaglement of two spin-$\frac{1}{2}$ particles: Let them be in singulet-state relative to an arbitrary axis (say z-axis): $$|\Psi \rangle = \frac{1}{\sqrt{2}} (\ |\uparrow_z, \downarrow_z \rangle - |\downarrow_z,\uparrow_z\rangle \ )$$ The ...

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Quantum entanglement of two particles is a way of stating that there exists a unique quantum mechanical solution ( a mathematical function) that describes the probability of finding the particles with specific attributes at specific spacetime points with specific energy and momentum. The probability is what is described/known/fitted. The shorthand of ...

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Entanglement isn't about interaction or information transfer betweeen entangled particles. Consider spin-entaglement of two spin-$\frac{1}{2}$ particles: Let them be in singulet-state relative to an arbitrary axis (say z-axis): $$|\Psi \rangle = \frac{1}{\sqrt{2}} (\ |\uparrow_z, \downarrow_z \rangle - |\downarrow_z,\uparrow_z\rangle \ )$$ The ...

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Instant communication is still impossible because the transfer of information occurs when the sender measures the quantum state of their photon. That causes the receiver’s entangled photon to instantly change. However, in order to understand the information, the receiver has to know what the original measurement was, along with some other instructions. ...

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It is real, and experimentally verified. If you measure the spin of entangled particle A, particle B when measured will always have the opposite spin. Some physicists believe it has to do with superluminal communication, but there are many other theories.

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"I was wondering if this type of communication..." Jimmy, as everyone has explained, you can not use entanglement to communicate information. (This is really unfortunate, but that's how it is!) There are many long explanations of this around, that make a good read. Regarding the entangled pair collapsing, I think it's perfectly reasonable to describe ...

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Let me first say that I do not work in quantum foundations, really, so I might have a few misconceptions myself. I beg anyone to correct me, where I err and I will try to provide more references upon request. After the question seems to have cleared up in chat, let me rewrite my answer: You basically seem to ask: What if entanglement would allow ...

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To entangle a system of two particles with two states each, not-yet-decayed and already-decayed, you need to put them into a superposition of these two states and have their states at least partially depend on each other. Basically, you can have states of the type that either both or none have decayed yet (but you do not know if either has), or of the type ...

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Not really. It is indeed perfectly possible to entangle two particles A and B without using direct interactions between them, the easiest example being to entangle A with some ancilla system C, carry C over to B, and then swap the states of B and C, which will transfer the A-C entanglement onto the A-B pair. This is of course not magical at all, and the ...

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Entanglement means that the particles involved are in a quantum mechanical state where all the phases and values are known. Take a specific decay of one particle into two. In the case of the pi_0 two photons come from the decay and their spins are "entangled" because pi_0 has zero spin and angular momentum has to be conserved. Both photons go at the ...

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Entangled particles simply do not have the information you think they have. Consider the simplest case, a particle that could spin up, down, or be in a superposition of both (this truly is as simple as it gets). If you have two particles, one possibility is that they each have those properties. For instance the first one could be up, the second could be ...

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This is not possible. Please look at the following links: http://physics.stackexchange.com/a/170798/75518 http://physics.stackexchange.com/a/154051/75518 http://physics.stackexchange.com/a/170884/75518 http://en.wikipedia.org/wiki/No-communication_theorem The first describes in a good way what entanglement is (statistical correlation). The second gives a ...

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What "entangled" means You probably have put too much in your head for the meaning of the word "entangled." Let me fix that for you: Two systems are entangled in quantum mechanics if the results of separate experiments on those two systems display strange correlations when you bring them back together and compare them. Notice that not all correlations can ...

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No idea if applying Fock algebras to the entanglement description would lead to anything "fruitful", I haven't seen any of that. What I've seen is the emergence of Tensor Network Methods in order to describe entanglement of many-body systems. There is the possibility that TNM can be related with holographic descriptions of gravity. Here is an ...

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For $z=2$ there is a study here http://arxiv.org/abs/quant-ph/0404026 in the context of ferromagnetic spin chain. The result is basically $\log L$. Swingle and Senthil argued in http://arxiv.org/abs/1112.1069 that "generally" the violation of area law for EE is at most $L^{d-1}\log L$ where $d$ is the space dimension. However, http://arxiv.org/abs/1408.1657 ...

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