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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Coincidence count probability in the entanglement-enabled delayed choice experiment

I'm trying to understand the entanglement-enabled delayed choice experiment and I'm kind of stuck at the term "coincidence count probability" which I can't seem to find definition of. Their full set ...
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Entanglement and coherence

I have come across a wonderful review of entanglement by Chris Drost in his answer to this post. One part that left me puzzled was: (This post is merely an attempt to understand a portion of Chris' ...
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In a superradiant laser, how does the collective dipole store the coherence of the photons?

In a standard laser, the stimulated emission is largely incoherent. How does a superradiant laser get around this? To my understanding, a magnetic field is usually applied to align the dipole moments ...
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Is quantum entanglement functionally equivalent to a measurement?

I saw the following talk the other day: http://www.youtube.com/watch?v=dEaecUuEqfc&feature=share In it, Dr. Ron Garret posits that entanglement isn't really that "special" of a property. He ...
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Which is a good and short book for foundations of quantum mechanics? [duplicate]

I am looking for a book that has stuff on quantum states, entanglement, etc. I am aware of the book, Geometry of Quantum States. I have read Ballentine's book, Quantum Mechanics: A modern development ...
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What is the greatest observed distance between clearly entangled particles?

As far as I can understand, decoherence will break entanglement. Given that, what is the greatest distance between entangled pairs, that has been successfully observed? Is it possible to identify ...
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Quantum indirect measurement with probes

I am wondering about the following hypothetical example regarding quantum measurements made by probes: An open, two-plate capacitor, in a LC circuit, has charge, q, that we want to measure. Each of ...
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What is the “monogamy principle” in enganglement?

What does the "monogamy" principle imply? At a superficial level, it seems to say that a particle can be entangled with at most one other particle. However, I keep reading that several particles are ...
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If Alice is moving at relatavistic speeds compared to Bob, is collapse still simultaneous?

I have read some papers about experimental proof of non-locality involving a laser that goes through a beam-splitter and then each "half" goes to an observer (traditionally "Alice" and "Bob"). It has ...
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301 views

Impulse travelling faster than light [duplicate]

There have been conducted many experiments in which light impulses traveled faster than light like the one in Princeton in 2000. This phenomenon has something to do with quantum entanglement. Does ...
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Quantum entanglement and information transfer: Does particle separation process set speed limit?

Background I recently read that a group had managed to overcome both the communication loophole and the detection loophole for Bell's theorem. In reading the article, I started to think about another ...
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Entangled systems and heat

Suppose I have two extended bodies that are entangled to each other. Are the thermal properties of the objects affected in some way by entanglement? For example, Imagine that one of the entangled ...
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Trace representation of density matrix question [closed]

System $A$ and system $B$ form a composite system. https://en.wikipedia.org/wiki/Partial_trace I wonder why $\rho_{AB}$ cannot be represented as $(\text{tr}_{B}(\rho))\otimes ...
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How are the photon and electron entangled in this situation? [duplicate]

If one of the photons in an entangled pair produced in parametric down conversion is absorbed by an electron or atom than this elecfron must be entangled with tge other photon. In what degree of ...
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Creation of entangled electrons

If one obtains two entangled in polarization photons by parametric down conversion and one of them is accepted by and electron 1 and other by electron 2 - are this electrons now entangled in spin?
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can extra dimensions explain the non locality of entanglement? [closed]

This is the question of layman fascinated by quantum theory. Entanglement of particles far apart from each other (relative to the speed of light) has been addressed in some other questions where the ...
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Entangled spins in a uniform magnetic field

I have been trying to calculate the time derivative of the expectation value of the operator representing the spin components of a a singlet state (e.g. sigma(z)tau(z)). I formed the tensor product of ...
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Is it appropriate to attribute an entangled state description to only one trial?

According to a popular definition a system is called "entangled" if its quantum state cannot be factored as a product of states of its individual distinct ("local") constituents (e.g. individual ...
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Quantum entanglement and Compton Effect

Suppose we generate 2 entangled photons (via a beam-splitter or similar apparatus). They have an arbitrary indeterminate initial frequency $\nu_i$. One of these photons is allowed to propagate through ...
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Does the violation of Bell inequality by a classical field imply “classical entanglement”?

This article has been brought to my attention recently (free access) : Shifting the quantum-classical boundary: theory and experiment for statistically classical optical fields In the abstract, they ...
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Entangled electrons seem impossible

Two fermions cannot share the same quantum state. But two electrons can be entangled. Entangled electrons share the same quantum state. Thus a contradiction. Where is my error?
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How does QFT help with entanglement?

I'm a bit confused. QFT is claimed to incorporate both Quantum Mechanics and Special Relativity. Therefore it should address the problem of non-locality caused by entanglement. However when I search ...
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Need help understanding delayed choice and entanglement swapping

From delayed choice experiment The results of all four measurements are then compared. If Victor did not entangle his two photons, the photons received by Alice and Bob are uncorrelated with ...
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Is it possible to use the observation of wave function collapse as a basis for superluminal communication?

I'm guessing the answer is no ;) but figured I'd ask anyway. Suppose I have one partner in an entangled pair and my friend on Alpha C has the other. I measure an observable (spin?) and the wave ...
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Quantum Entanglement: how to generate 2 entangled particles?

I get quantum entanglement but I don't quite get how one would go about generating two complementary particles that are entangled (a photon and its entangled sibling, an electron and its entangled ...
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Quantum entanglement and information transfer

I know it was stated many times that information transfer using entanglement is not possible and I am most probably wrong but I would be glad if you can at least point me to where I am mistaken. If ...
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Checking correctness of partial trace

I am doing some simulations that requires me to take partial trace over a three qubit density matrix $\rho_{ABC}$. I find the mixed state density matrix of one qubit by tracing out the other two, ...
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How to discern that a subsystem of entangled system is in a mixed state

We have a an entangled system, composed of two subsystems, $A$ and $B$, in a pure state $|\Psi\rangle$, in a basis $|ab\rangle$, described by wave function $\Psi(a,b)$. Density matrices are written as ...
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How does entanglement work independent of time?

A recent experiment shows that it is possible to entangle two particles that never co-existed in time. Time line diagram. (I) Birth of photons 1 and 2, (II) detection of photon 1, (III) birth of ...
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Local operation on bipartite quantum system [closed]

Suppose we have a state: $$ |\Psi_{1234}\rangle = \frac{1}{2}\left(|\Psi_{14}^+\rangle \otimes |\Psi_{23}^+ \rangle + |\Psi_{14}^-\rangle \otimes |\Psi_{23}^- \rangle - |\Phi_{14}^+\rangle \otimes ...
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Correlated bell states

I have a question about terminology. What is the terminology for describing 2 correlated bell states shared by 4 qubits?
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Entanglement swapping and Bell state analyzer

In entanglement swapping where AB from two entangled pairs AC and BD are projected into Bell state by Bell state measurement (https://en.wikipedia.org/wiki/Bell_state#Bell_state_measurement) on A and ...
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Question about Bell state analyzers

Is there a Bell state analyzer that would take as input 2 qubits in Bell state, distinguish between psi and phi states and send psi states to output A and phi states to output B?
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Discriminate between bell states

Is it possible to discriminate between 2 of the four Bell states (phi, psi) and does it interfere with the entanglement?
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Interferometric Entanglement of path and spin

I am looking at a problem where I can have a spin 1/2 particle in either a |1$\rangle$ or a $|0\rangle$ state in an interferometer (0 is one arm and 1 is the other). And the spin 1/2 follows the ...
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Size of Objects in entanglement

Pardon the possible obviousness of my lack of understanding entanglement but how big have we noticed the objects in the system whole? We talking particles or can planets or universes be entangled? ...
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Does entanglement entropy remain constant?

So I am trying to figure out what the time derivative of entanglement entropy is $$\frac{d}{dt}(-Tr[\rho^A\log_2\rho^A])$$ Where $$\rho^A=\sum_{aa'}|a\rangle\langle a'|\sum_bc_{ab}c_{a'b}^*$$ And ...
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Quantum entanglement continuous measurement

Is there a possibility (if not real than at least theoretical) that we could measure the spin of an electron continously over some (even very short) period of time, so that it does not change during ...
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Is physical contact necessary for entanglement

My question is as follows: Is it absolutely necessary for particles to come into contact before they can be entangled? Has any experiment reported of particles which were never in contact showing ...
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Quantum entanglement correlations [closed]

I have a vague idea of what entanglement is but I am stuck at one place: we all know that entanglement is destroyed with time. this is called decoherence. I wish to know if there is any correlation ...
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Popular books on cutting-edge physics [closed]

I watched this video, in which different types of topics are discussed like Quantum Information, Quantum Computation, Universe as hologram, Hidden information, Quantum Entanglement, Black holes and ...
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What's the difference between an entangled state, a superposed state and a cat state?

1) Can a state be entangled without also being a superposition? (Please give an example.) 2) Can a state be a superposition without being entangled? (Again, an example please.) 3) And what about ...
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Indirect probing of entanglement measures

Entanglement is a purely quantum mechanical phenomena that e.q. increase precision of quantum interferometers, atomic clocks or have application in quantum computing. There are many "measures" of ...
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When can a Hilbert space with a given Hamiltonian be decomposed into non-interacting tensor product factors?

Let's say I have a Hilbert space $\mathcal{H}$ (either finite-dimensional or with a countably infinite basis) with a specified Hamiltonian $\hat{H}$, representing some quantum system. Under what ...
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Why can't be the EPR experiment simplified?

Alice measures the spin of her electron on the x axis. She now knows the spin value of Bob's electron on the x axis at time T0. Bob measures the spin of his electron on the z axis. He now knows the ...
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Entanglement of coherent states

I am new to quantum optics and I am trying to understand whether coherent states of the field could be entangled. Let's consider, for example, a two-mode state: $|\psi^{AB} \rangle = \frac{1}{c} ...
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Separability of density operators on tensor product spaces

Consider a composite system $\mathcal{H}=\mathcal{H}_{A}\otimes\mathcal{H}_{B}$ where $\mathcal{H}_{A}$ and $\mathcal{H}_{B}$ are Hilbert spaces of constituent components (say two qubits). Let ...
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Why would hidden variables in Bell's Stern-Gerlach experiment related to entanglement require only 4/9ths of the measurements to be equal?

Bell's Stern-Gerlach experiment, consisting of 2 sets of detectors each with 3 randomly chosen detection directions, is one of the most important experiments cited as proving that entanglement has ...
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How was it proven that a quantum entanglement measurement of particle A, affects properties of particle B

If I understood the wikipedia article correctly, quantum entanglement claims that information travels instantly between entangled particles. An act of measurement on one of the entangled particles ...
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Speed of entangled particle changes [duplicate]

If two particles are entangled at a distance of light years, does changing one affect the other instantaneously, or does it take years to occur? What gives us the answer to this question?