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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Given entanglement, why is it permissible to consider the quantum state of subsystems?

Quantum entanglement is the norm, is it not? All that exists in reality is the wave function of the whole universe, true? So how come we can blithely talk about the quantum state of subsystems if ...
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Backward causality: A question/extension to Ma et al.'s “Experimental delayed-choice entanglement swapping”

In a philosophically rather interesting experiment, Ma et al. show that backward causality exists in quantum physics. An Ars Technnica-article gives a less technical account. From Ars Technica: ...
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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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Would Quantum entanglement theoretically allow prediction of the future?

This article describes how a choice made by the recipient of an entangled photon can affect measurements taken on that photon's "partner" before the decision was made. So let's say there are two ...
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796 views

Entanglement spectrum

What does it mean by the entanglement spectrum of a quantum system? A brief introduction and a few key references would be appreciated.
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397 views

Entanglement and relativity

Two observers A and B measure a quantum entangled state and obtain correlated results, even if their separation is space-like (each is out of the light cone of the other). A possible interpretation is ...
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710 views

Does this Zeilinger group result provide experimental proof of backward-in-time causation?

Does this recent Zeilinger group delayed choice entanglement experiment imply backward-in-time influences? http://arxiv.org/abs/1203.4834 From the abstract: "This can also be viewed as “quantum ...
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577 views

Entanglement in time

Quantum entanglement links particles through time, according to this study that received some publicity last year: New Type Of Entanglement Allows 'Teleportation in Time,' Say Physicists at The ...
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200 views

Entanglement and conservation

Is the following assertion sufficiently unique to merit a paper? Every absolute conservation law implies a corresponding form of entanglement, not just spin (angular momentum). Linear momentum ...
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134 views

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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777 views

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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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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461 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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257 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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162 views

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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310 views

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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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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136 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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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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571 views

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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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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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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476 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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455 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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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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659 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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441 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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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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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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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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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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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 ...