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Questions tagged [quantum-entanglement]

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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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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Is there a way to obtain an RG flow equation for Quantum spin systems using MERA

We restrict ourselves to ground states of translationally invariant 1d quantum systems. I understand that there is the scale invariant MERA(multiscale entanglement renormalization ansatz) which ...
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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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A question regarding Leonard Susskind's ER=EPR lecture

https://youtu.be/OBPpRqxY8Uw?t=1315 Right at this instance of the video Susskind starts talking about how space is actually connected by entanglement. (You should watch the video for a accurate ...
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Entanglement inequality (Gaussian vs. non-Gaussian states)

I'm considering a quantum system with $N$ bosonic degrees of freedom labelled by pairs $(x^i,p^i)$, such that the Hilbert space is $\mathcal{H}=L^2(\mathbb{R}^N)$. Given an arbitrary quantum state $|\...
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Geometric measure of entanglement for fermions or bosons?

For a system consisting of multiple components, say, a spin chain consisting of $N\geq 3 $ spins, people sometimes use the so-called geometric measure of entanglement. It is related to the inner ...
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Entanglement g-2-experiment - Which components do I need?

I would like to measure whether my source emits entangled photon pairs. To that order I want to build a g-2-experiment, which measures photon coincidence counts as a function of time delay between ...
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Information scrambling and Hawking non-thermal radiation states

Could a very small black hole where half of its entropy has been radiated, emit Hawking radiation that is macroscopically distinct from being thermal? i.e: not a black body radiator. Or would the ...
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Which interactions produce entanglement?

I'm trying to better understand which kinds of interactions cause the entanglement. I do understand how it works in the cases of non-relativistic spin systems. For example, evolving a pure state in ...
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Von Neumann entropy in the algebraic approach

In the algebraic approach to QM a quantum system has associated to it one $\ast$ algebra $\mathfrak{A}$ generated by its observables. A state is a positive, normalized linear functional $\omega : \...
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What is some good reference for tensor network?

I am a physicist who is now doing some research in quantum information, which might involve tensor network.
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Black holes in AdS/CFT

In Swingle's work Entanglement Renormalization and Holography, he mentioned that a black hole in AdS bulk corresponds to a finite temperature boundary state. With the MERA picture of the entanglement ...
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What is the difference between microscopic quantum interference between photons and macroscopic interference between laser beams?

To get interference between laser beams we use an interferometer composed of mirrors and one beam splitter. To get interference between photons we use an interferometer composed of polarizers, ...
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Standard references in (holographic) entanglement entropy literature (Part 1)

While writing a paper, I am wondering as to what are the standard references that one refers to for these various facts about entanglement entropy. I want to know as to what are the papers one should ...
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What are the requirements on conditional unitaries for overcomplete bases?

On way to describe "pure" decoherence (that is, decoherence with respect to a basis that doesn't involve transitions between basis states) between a system $\mathcal{S}$ and an environment $\mathcal{E}...
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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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What is the relationship between spin network spacetime and tensor network (entanglement) spacetime?

In 1971, Sir Roger Penrose, suggested a combinatorial construction of spacetime using the angular momentum of particles. This work led to and introduced the idea of spin networks which are ...
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Tensor Network from Lattice

I read an article about tensor networks and they seem very interesting and a promising approach to studying the relations between entanglement, gravity and quantum information. How does this network ...
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Entanglement and the Interaction Hamiltonian

I understand that entanglement is irreversible, due to loss of information. I also believe that, at least sometimes, it can be produced using an appropriate "interaction hamiltonian", $\hat{H}_{int}$, ...
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Is there a name for $I(A:B)-I(A:C)-I(A:BC)$ in (quantum) information theory?

Let $I(X:Y)=S(X)+S(Y)-S(XY)$ be the mutual information between $X$ and $Y$, where $S(X)$ is the entropy of $X$ (say the entanglement entropy of subsystem $X$ in quantum information). To characterize ...
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What has quantum entanglement to do with navigating on the magnetic field?

In this video is simply explained how robins use the magnetic field to navigate. But the author is talking about quatum entangelment, but I don't see how this is related to navigating. Now there are ...
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Entanglement of formation for two qutrits

For a pure bipartite state $|\psi\rangle\in\mathbb C^d\otimes \mathbb C^d$, the entanglement is given by $E(|\psi\rangle) = S(\mathrm{tr}_B|\psi\rangle\langle\psi|)$, with $S(\rho)=-\mathrm{tr}(\rho\...
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How to create quantum entangled electrons

I understand that one way of creating quantum entangled electrons is by splitting a Cooper pair. Is then their spin property used in the measurement, as this must always sum to $0$? If that is the ...
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What is a maximally entangled state? Or better, what really is entanglement entropy?

I was trying to understand the concept of entanglement entropy and for that I was studying the density operator formalism in the context of a bipartite quantum system. In some references, people ...
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How does gravity affect entanglement?

Hypothetically an entangled pair of atoms are placed inside two similar satellites orbiting at the same altitude, one of the satellite will then slow its speed and descend towards the surface of Earth....
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Are Cosmic Microwave Background (CMB) photons entangled?

Suppose we'd like to know whether two cosmic microwave background photons emitted from different parts of the sky have any quantum correlation with each other. We could measure polarization of two ...
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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, $ds^2 ...
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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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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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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, e....
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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 (13)...
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Will entangeld particles stay entangled?

I want to consider an experiment: We create two entangled particles a and b such that the spin of each is opposite to the other. We then measure spin in z direction (1). So we get a is up and b is ...
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$k$-local Hamiltonian with long range entangled ground states?

Is it possible, and if yes, is there a relatively simple example of a Hamiltonian that only has k-local terms but its ground state always has entanglement beyond $k$ sites? For instance if $H = H_{...
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Symmetric Quantum Discord

Let's define the symmetric quantum discord in the following way: $$D(A:B):=\frac{1}{2}(D(A|B)+D(B|A))$$ where $D(A|B)$ is the usual quantum discord given as $$D(A|B) = I(A:B) - \mathcal{J}(A|B)$$ ...
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Entanglement fidelity for a single qubit?

So I have been working out problems from the book "Quantum Computing Explained" by David McMahon. On page 166 he defines "Entanglement Fidelity" and says the following: Consider a density operator for ...
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Squeezed state in Fock basis

I'm learning quantum optics, and I'm starting to manage boson algebra. In particular, as a pure exercise, I would like to express a squeezed vacuum state in the Fock basis, which, according to ...
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Can we use entangled black holes to form wormholes?

If any object can be made black hole by crushing it to its Schwarzschild radius, can we do the same process in two different points in the space keeping the quantum states of both the objects ...
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How Forces are Represented from Quantum Computation or Entanglement Perspective?

In the fields of Quantum Computation and Entanglement there is content on the structure of quantum systems and artificial quantum systems like qubits and quantum cellular automata. I have even seen ...
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Can scatter interference patterns from entangled pairs carry information?

I am having problems wrap around why you can't send information faster than light with a similar setup to the quantum eraser experiment. ( https://arxiv.org/abs/quant-ph/9903047v1 ) What I mean is, ...
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Teleportation and boosted observer, special relativity

According to relativistic quantum information, entanglement, purity of states are not Lorentz invariant. Here I check such a problem. If we have two coordinate systems $R_A,R_B$ with relative ...
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How does a non-local unitary operator differ from a local one?

I know that entanglement is conserved under local unitary operations, but haven't heard a lot about their non-local counterparts. Recently, I read that a CNOT gate which is unitary, can create ...
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About complexity of quantum states

From quantum computation point of view, the complexity of a quantum state $|\psi\rangle$ can be defined as the the complexity of the quantum circuit that can generate the state $|\psi\rangle$ from an ...
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Are all instances of quantum non-locality problem artifacts of the use of classical concepts in quantum physics?

Consider experiments involving entangled spins, say two-spin 1/2 particles in the singlet state: $$\left|\psi\right> =\frac{1}{\sqrt{2}}\left[\left|\uparrow\downarrow\right> - \left|\downarrow\...
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In the case you entangle two free protons, how are the quarks in one proton entangled to the quarks in the other proton?

The three quarks (uud) in a proton are held together by the strong force, and the overall e.m. force between the quarks is repulsive but much weaker, so the quarks stay together. Now two free ...
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Question about general direction of development of application of Tensor Networks to AdS/CFT

I am quite interested in the area of application of Tensor Networks(TNs) to AdS/CFT correspondence. I would like to clarify certain points in order to get better general picture. What is the main ...
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Quantum Entanglement Simulation

Suppose there is a digital "quantum entanglement simulator" with a pair generator and two spin detectors, and it Allows to create as many pairs as you want (100 pairs per single click) Allows to ...
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Entanglement of bi- and tripartite pure and mixed states

since I'm not sure on how to find out whether a system is entangled or not I thought about examples that could clarify the whole thing. first example: system is in the state $\rho=1/2 (| 000 \rangle \...
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What is the significance of the assumption of “full energetic degeneracy” in this paper?

I'm reading the new paper "Foundations of statistical mechanics from symmetries of entanglement" (available on arxiv), in which the authors Deffner and Zurek note that the quantum microcanonical state ...
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The link between non-locality and Heisenberg's uncertainty relations

I have recently found out1 that the concepts of non-locality and Heisenberg's uncertainty do not live independently of one another in Quantum Mechanics. In other words, roughly the idea goes as: the ...
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What is the relationship between coherent states and quantum coherence?

What is the relationship between coherent states and quantum coherence? To me coherent states were only talked about in regard to Quantum Harmonic Oscillator, whereas coherence and decoherence on the ...