Quantum entanglement is the mechanism by which quantum correlations between two sub-systems survive even after being physically separated from an interaction region. The correlations could in principle survive without neither time nor space constraint.

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Defining entanglement in subspaces of tensor product

I have asked the question in math.stackexchange, but perhaps it should be more relevant here. Hence I am re-posting it with necessary reediting. Let $\mathcal{H}=\mathbb{C}^n$ be a Hilbert space. A ...
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Entanglement: Is it possible to prepare and reset probabilities to send information?

I'm pretty certain that the answer to the question in the title is a no, but I don't understand why. I have some basic misunderstanding of quantum processes that I’d like clarified in the form of ...
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Coincidence detectors in Bell tests: How close is close enough?

When is a coincidence a coincidence? We know that to identify entangled photons, the electronics is set to look for simultaneous clicks at opposite detectors. The size of the window is to some degree ...
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Questions about entanglement from a laymen/quantum hobbyist

Please note I am not a physicist I just read every article I can on it, I understand a good amount on it though. But no maths. (currently trying to learn the maths) By what means can we as humans ...
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Quantum entaglement and the arrow of time

I have seen several claims to that quantum mechanics is required to explain the arrow of time which I take to mean the macroscopic irreversibility of physical systems. This is presumably to resolve ...
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ER = EPR and Time Travel

In Maldacena-Susskind paper arXiv:1306.0533, they propose an idea of $$\text{ER = EPR}$$ the relation between the wormhole and the quantum entanglement. which ER means Einstein Rosen (ER) bridges, ...
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Questions on entanglement entropy

If the spatial entangling surface is $M$ then it seems that one way to get the entanglement entropy is to think of the QFT on the manifold $S \times M$ where $S$ is a 2-manifold with the metric, ...
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Entanglement entropy of 1D chiral Fermion

I was told that the entanglement entropy $S_E$ on the ground state of a (1+1)D conformal field theory (CFT) follows the logarithmic behavior $S_E=\frac{c}{12}\ln L$ where $L$ is the length scale ...
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Concurrence in higher dimensions?

Does anybody know of any calculation of the concurrence for some mixed state other than the qubit-qubit case (which was solved by Wootters)?
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Spin polarization of decay products

A relativistic moving particle, e.g. muon $\mu^+$, described by its four-momentum vector $p_\mu$, charge $e$ and with a given spin polarization, ${\bf S}=(S_x,S_y,S_z)$, decays into three particles, ...
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Why do we think that quantum entanglement implies action at a distance? [duplicate]

Possible Duplicate: Why quantum entanglement is considered to be active link between particles? I am a layman trying to read into quantum mechanics. As I understand it quantum entanglement ...
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Has anyone actually “seen” entanglement?

I want to know if the following has been done experimentally; after the spin (or any other characteristic with a probability of 50%) of 2 entangled particles has been measured, we change the spin of ...
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Does measuring destroy entanglement

Before measuring a quantum particle(photon) it exists in a superposition state, once we observe(measure) it, it settles in one of the possible states(destroying superposition). For entangled ...
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Is it possible to bind an entangled electron to the outer shell of an atom or just a proton?

Say we start with an entangled electron--positron pair and we separate them. I want to take the entangled electron and bind it to a proton or the outer shell of an atom. Is it possible to do this ...
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Why can't we use entanglement to defy Heisenberg's Uncertainty Principle?

In principle, it is possible to entangle any property of two particles, including speed and momentum. Surely then, this could be used to defy the Uncertainty Principle, which states that the momentum ...
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What is the difference between Quantum teleportation and Radio waves?

Quantum teleportation over 143 kilometres using active feed- forward What is the difference between Quantum teleportation and radio waves?
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What is time teleportation?

I read this article about time teleportation. Can someone explain the concept better?
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Von Neumann Entropy: varying definitions

I have seen different authors define von Neumann entropy in different ways. In particular, some use the natural logarithm and others log to base 2. What is the reasoning for this? Does it make any ...
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Coherence, Entanglement, Correlation

Let's deal specifically with a two-level system. I understand that ``coherence'' is due to the off-diagonal elements in the density matrix $\rho(t) = \sum_{i}|\psi_i(t)\rangle p_i\langle\psi_i(t)|$ ...
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What properties are entangled in quantum entanglement?

When two particles are entangled, one can measure the properties of one of the particles and instantaneously know the properties of the other. This is because the two particles possess the same ...
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What does the notation $|x_1,x_2\rangle$ mean?

I would like clarification on an equation in the paper "Free matter wave packet teleportation via cold-molecule dynamics", L. Fisch and G. Kurizki, Europhysics Letters 75 (2006), pp. 847-853, DOI: ...
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Can two distinct spatially separated many-body systems in the ground state contain entangled particles?

In particular, I am asking if two distinct many-body systems (e.g. system A and system B) separated at some arbitrary distance will necessarily be found to contain entangled particles (such that ...
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Spin up, spin down and superposition

I'm just starting to study quantum mechanics. Please explain the error in this thinking: You set up decay of two $\pi$ mesons and get $2\mathrm{e}^-$ on Mars and $2\mathrm{e}^+$ on Earth. On Earth ...
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Local measurement of entangled particle pairs and interpretation of state

This just started to bother me after reading yet another entangled particle question, so I hate to ask one myself, but... If we have two entangled particles and take a measurement of one, we know, ...
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What are the benefits of quantum information “teleportation”?

I read occasionally popular science articles and from time to time encounter issues about quantum information teleportation. (this one for example http://www.physorg.com/news193551675.html) So far I ...
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How could there be a truly “pure” state?

If the Universe did start from a single point, then wouldn't all particles be fundamentally entangled? How then could there be a truly "pure" state?
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A (mundane) CS analogy for quantum teleportation

From my limited understanding of quantum entanglement, it seems like qubits act the same way as pseudo-random-number-generators (except as far as we can tell, these ones really are random). When you ...
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Deriving entanglement entropy from Renyi entropy

My questions are based on this paper - http://arxiv.org/abs/0905.4013 Firstly I want to know as to whether some assumptions are needed about the relationship between the systems $A$ and $B$ for the ...
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Does the reduced density matrix describes a real mixed state?

Suppose that we have two entangled particles A and B with pure state vector $|\psi\rangle=a|0\rangle_A |1\rangle_B + b|1\rangle_A |0\rangle_B \hspace{1cm}(1)$ When we take the partial trace over the ...
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What is “quantum locking”?

I've always assumed that "quantum locking" was a term invented by the writers of Dr Who, but this video suggests otherwise. What is quantum locking? Is it real?
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Weak measurement and Hardy's paradox

How the notion of weak measurement resolves Hardy's paradox?
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Measuring Entangled Qubits

Suppose we have a pair of entangled qubits. $$ |\psi\rangle = \frac{1}{ \sqrt{2} } ( |00\rangle + |11\rangle ) $$ Now we give one qubit to Alice and other to Bob. Alice measure the her qubit to ...
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Is it possible to send a single photon from a distant planet (say Mars) and detect its arrival at a site on Earth?

My question is specifically whether there exists a technique by which a single photon can be "tagged" or "encoded" in such a way that it can traverse our atmosphere and arrive at some sort of detector ...
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What is the defining property for two quantum states to become entangled?

What is the defining property for two quantum states to become entangled? Is it just that the combined system cannot be in a product state? Why is this?
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Can we determine whether or not a particle is entangled?

Suppose Shaniqua and Tyrone have four pairs, a, b, c, and d, of entangled particles. They take their particles and go very far apart. If Tyrone can determine whether or not a particle is still ...
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Quantum entanglement on cosmological scales

This may be a foolish question given my limited understanding of QM but here it is. As I understand quantum entanglement basically means that two particles evolve as a single "unit", i.e., are ...
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Thought experiment using quantum entanglement in position and its effects

Consider we have two atoms $a$ and $b$. They are entangled with each other in position and momentum, with some wavefuction describing them in position space that is $\Psi(x_a, x_b)$. This ...
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Entanglement in single particle state

Is it possible that we have entanglement in different degrees of freedom of a singe particle. like spin and linear momentum .
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Free Will Theorem question

The Kochen-Specker Theorem says, if I understand it correctly, that the results of spin measurements cannot be predetermined independent of measurement. They get to this conclusion by describing 33 ...
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Double slit experiment and entanglement

Just wondering, what would happen in this experiment. In the experiment you would first have two entangled particles. Then you fire one of the particles, lets say "Particle A", at a double slit ...
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What quantum states can be measured using entanglement?

I have been reading about quantum entanglement, and I was wondering what quantum states can be "sent" using entanglement. I know you can measure the spin of one of the particles, and know the spin of ...
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Entanglement and Black holes

If you have two entangled quantum states, One state falls into a black hole and you measure the other state, What can you say about the state that has fallen into the black hole? If you have billions ...
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Trotter splitting and entanglement entropy

I have heard that a numerical solution to the Schrodinger equation using the Trotter splitting formula for a many-body Hamiltonian can cause an artificial increase in the entanglement entropy. I was ...
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How to make timelike entanglement in the laboratory?

http://io9.com/5744143/particles-can-be-quantum-entangled-through-time-as-well-as-space http://arxiv.org/abs/1101.2565 How to make timelike entanglement in the laboratory? How to test whether mixed ...
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Are the electrons in a quantum hall edge state entangled?

I am reading the paper on Quantum Energy Teleportation by Yusa, Izumida and Hotta(This article), and it seems that they are assuming that the quantum hall edge state is a quantum correlated state, ...
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Separable states of maximum non-classical correlations

Although there is no standard measure of entanglement, the GHZ states $|GHZ\rangle=\frac{1}{\sqrt{2}}(|0\rangle^{\otimes n}+|1\rangle^{\otimes n})$ are often deemed as maximally entangled states of ...
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Does the passage of time effect a photons entanglement with another?

I recently read an article about "Delayed-choice entanglement swapping". Here is an excerpt from the article: Delayed-choice entanglement swapping consists of the following steps. (I use the ...
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How can one trace out polaritonic degrees of freedom?

I have read the paper "Steady state entanglement between hybrid light-matter qubits", arXiv:0711.1830v2. There, writers obtained density operator in matrix form after solving steady state equation ...
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What is coherence in quantum mechanics?

What are coherence and quantum entanglement? Does it mean that two particles are the same? I read this in a book called Physics of the Impossible by Michio Kaku. He says that two particles behave in ...
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Does entanglement have a speed or is it instantaneous

The phenomenon of observing one entangled particle and noticing the other take on corresponding values... Does this take a finite speed at all or is it instantaneous?