Quantum entanglement is the phenomenon of two particles depending on each other, once they have interacted, even after becoming physically separated.
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Quantum entanglement of spin along multiple orthogonal axes
Picture an entangled pair of spin 1/2-spin particles with total spin 0. In the diagram, particle 1 of the pair is moving to the left (-y), and particle 2 to the right (+y).
If a z-oriented SG$^*$ is ...
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Is a macroscopic pair where I observe one of them quantum entanglement?
Of what little I know/understand about quantum entanglement can somebody confirm if the following experiment is a good analogy to quantum entanglement of pair of particles? PS: please don't laugh as ...
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Energy Measurements in a Two Fermion Double Well System
This question is related but my question here is much more elementary than discussions of the Pauli principle across the universe.
There has been a fair amount of discussion around at the moment on ...
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142 views
Thought experiment with entangled electrons
Suppose we start out by having two entangled electrons. We separate them by some distance and we put one electron inside a thin loop of wire connected to an extremely sensitive voltage measuring ...
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281 views
Entanglement and the double slit experiment
Is the double slit experiment an example of entanglement when it seems as if the photon is going through both slits? Or put another way, is it at this stage when we attempt measurement we see a photon ...
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143 views
Can the concurrence be calculated in terms of the entanglement of formation?
If I somehow know the entanglement of formation, $E_F$ for two mixed qubits, where
\begin{equation}
E_F = -x \log x - (1-x) \log (1-x),
\end{equation}
where $x = (1+\sqrt{1-\mathcal{C}^2})/2$ and ...
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Are all classically impossible quantum possibilities entangled?
Any entangled state represents a quantum possibility that is classically impossible.
Is the converse true?
That is, are all states that are quantum mechanically possible but classically impossible ...
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Relativity and Entanglement
Say we have two particles which are entangled so that they have opposite spins. If one is up, the other is down. They are sent off to two spatially separated observers A and B. Both observers can ...
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Reduced density matrices for free fermions are thermal
Many recent papers study entanglement in eigenstates of fermionic free hamiltonians (normally on a lattice) using the basic assumption that the reduced density matrices are thermal (e.g. Peschel ...
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Do any entanglement measures for mixed states exist that use only single site correlation functions?
For a pure state $\rho_{AB}$, the entropy of entanglement of subsystem $A$ is
\begin{equation}
S( \rho_A) = -tr (\rho_A \log \rho_A)
\end{equation}
where $\rho_A$ is the reduced density matrix of A. ...
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449 views
Can cellular automata be reconcilied with quantum mechanics?
CAs are deterministic representations of the universe, which, according to the Bell's inequality are not entirely accurate. Cells interact "locally" (only with the closest neighbours), while quantum ...
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1answer
128 views
How Is Entanglement Created Among Qubits?
How are qubits entangled?
I understand the basics of entanglement but what I do not get is how it occurs in nature or in the lab. What causes entanglement to occur or what is done to the particle to ...
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37 views
Optimality of the CHSH strategy
The maximum achievable probability of the Clauser-Horne-Shimony-Holt game is $\cos^2(\pi/8)\approx85.355\%,$ which can be proved with Tsirelson's inequality. But I don't imagine that this remained ...
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Quantum Computing, Qubit Creation/Entanglement
I am currently a high school student researching quantum computing. I was referred to this site by Google and a friend. Currently I am researching the qubit part of quantum computing. My question is ...
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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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1answer
76 views
Number of conditions for a two-particle state to be decomposable
Suppose we have a general two-particle state $ \Phi (x_1, x_2 ) = \sum_{n_1,n_2} \phi_{n_1,n_2}(x_1,x_2)|n_1,n_2> $, where $n_1$ can be any of $n$ possible states, and $n_2$ can be any of $m$ ...
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479 views
The mathematics of entanglement
I've finally managed to get a grasp on the Bell test experiments and all that they imply about our reality. Now I'm curious about the mathematical derivation which allowed Schrodinger to predict the ...
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398 views
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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CHSH violation and entanglement of quantum states
How is the violation of the usual CHSH inequality by a quantum state related to the entanglement of that quantum state?
Say we know that exist Hermitian and unitary operators $A_{0}$, $A_{1}$, ...
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1answer
324 views
A physical understanding of fractionalization
all! Is there a physical understanding of fractionalization in condensed matter physics? The textbook approach is theoretical, not physical. I'm thinking of spin-charge separation for electrons, the ...
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89 views
What Shannon channel capacity bound is associated to two coupled spins?
The question asked is:
What is the Shannon channel capacity $C$ that is naturally associated to the two-spin quantum Hamiltonian $H = \boldsymbol{L\cdot S}$?
This question arises with a view ...
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1answer
280 views
State of Matrix Product States
What is a good summary of the results about the correspondence between matrix product states (MPS) or projected entangled pair states (PEPS) and the ground states of local Hamiltonians? Specifically, ...
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A resource theory of quantum discord?
Local Operations and Classical Communication (LOCC) is the classic paradigm for studying entanglement. These are things that are `cheap' and unable to produce entanglement as a resource for a quantum ...
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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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Orbits of maximally entangled mixed states
It is well known (Please, see for example Geometry of quantum states by Bengtsson and Życzkowski ) that the set of $N-$dimensional density matrices is stratified by the adjoint action of $U(N)$, where ...
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Sub and super multiplicativity of norms for understanding non-locality
In relation to various problems in understanding entanglement and non-locality, I have come across the following mathematical problem. It is most concise by far to state in its most mathematical form ...
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Quantum entanglement faster than speed of light?
recently i was watching a video on quantum computing where the narrators describes that quantum entanglement information travels faster than light!
Is it really possible for anything to move faster ...
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363 views
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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1answer
170 views
Reeh–Schlieder theorem in QFT and entanglement in biological systems
Context: There have been a few papers out recently which mention how photosynthesis in plants might have connections to entanglement, or even perhaps that entanglement is causing photosynthetic ...
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169 views
Tracking photon color in Bell experiments
In parametric down-conversion, it is said that a driving photon is converted into two entangled photons whose frequencies add up to the driving frequency. Yet in discussions about entanglement ...
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1answer
180 views
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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Quantum entanglement vs classical analogy
Consider that we have two balls, one white and one black, and two distant observers A and B with closed eyes. We give the first ball to the observer A and the second ball to the observer B. The ...
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1answer
236 views
Constructing a maximally entangled qutrit state from $n$ Bell states
I've read that maximally entangled qubit states are a good "unit" of bipartite entanglement since it is possible to create any other entangled state from them using local operations and classical ...
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Can two entanglement particles satisfy at same time two different wave functions?
The wave function determines the probabilities of an outcome, and the wave function is parameterized "shaped" depending on the measurement set.
i.e. two different measurement set would lead to two ...
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Why is it valid to take the partial trace to describe a subsystem?
In derivations of decoherence, there eventually comes a point when we are asked to take the partial trace over the environment. Why should this be valid for an entangled system? Why should taking the ...
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Has quantum entanglement been demonstrated to be able to take place over infinite distances?
In my poor understanding of quantum physics, quantum entanglement means that certain properties of one of two 'entangled' quantum particles can lead to change over infinitely large distances when the ...
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1answer
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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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Can observations of entangled particles affect their unobserved counterparts?
There are two experiments that are often used to explain Quantum Mechanics: the two-slit experiment and the EPR paradox. I am curious what would happen if you combined them.
Imagine an experiment ...
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Expansion of multi-particle state vector as a sum of n-entangled states
Physically, quantum entanglement is ranged from full long-range entanglement (Bose-Einstein condensate), described by a basis of states that look like this:
$$ |\Psi\rangle = |\phi_{i_{0} i_{1} ... ...
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Quantum Computing and Animal Navigation
Someone sent me this link to a talk by Prof. Klaus Schulten from the University of Illinois: (my emphasis)
Quantum Computing and Animal Navigation
Quantum computing is all the rage nowadays. ...
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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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488 views
The Reeh-Schlieder theorem and quantum geometry
There have been some very nice discussions recently centered around the question of whether gravity and the geometry and topology of the classical world we see about us, could be phenomena which ...
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818 views
Vasiliev gravity and “holographic” entanglement
It has been proposed that AdS/CFT arises because of the entanglement structure of quantum field theories, e.g. see the discussion which occurred right here. Until now I have been skeptical of the ...
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1answer
355 views
Can PEPS explain the holographic principle in quantum gravity?
Condensed matter physicists have shown using quantum information that in many condensed matter systems, entanglement entropy only scales as the area of the boundary, and not the volume. This is the ...
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4answers
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Justification of ignoring large set of entanglements
If we can think about the universe as a wave function then many particles should be entangled with many other particles in the universe. The obvious question arises why we don't see those ...
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Conservation of energy in quantum teleportation
Consider the quantum state teleportation protocol of Bennett et. al.
How does one prove that this protocol would never violate the conservation of energy? At the face of it, it doesn't seem to be ...
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3answers
436 views
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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3answers
409 views
Entangled particles
So we have two particles (A and B) that are entangled.
From what I understand, entanglement isn't destroyed, it is only obscured by subsequent interactions with the environment.
Particle A goes ...
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1answer
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Unsolved entanglement problems
What are the current most important theoretical problems on quantum entanglement?
What is that we don't yet understand about how it works?
(Not considering interpretation etc problems)
