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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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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Are there more entangled states or non-entangled ones?

I'm trying to understand entanglement in terms of scarcity and abundance. Given an arbitrary vector $v$ representing a pure quantum state of, say, dimension 4, i.e. $v \in \mathcal{H}^{\otimes 4}$, ...
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87 views

Bell inequality violations evidence for 1935 EPR claims?

Is it possible that Bell inequality tests provide experimental evidence in support for the EPR claims in their 1935 paper titled "Can Quantum-Mechanical Description of Physical Reality Be Considered ...
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48 views

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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Entanglement, Bohr-Einstein Debate, Bell's Inequality

On BBC episode The Secrets of Quantum Physics (Part 1) Jim Al-Khalili explains quantum mechanics for the layman. In the first half, he does a very good job; in the second half, either he thought his ...
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What is an “antiquated” coherent state?

I am studying entangled coherent states. Some of the papers I looked up (for example http://www.global-sci.org/jams/open-access/v2n2/pdf/022-155.pdf) mention some special properties of entangled ...
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Communication via teleportation/entanglement (FTL communication)

I know this has been asked many times, but I have a hard time "crystallising" it in my mind. First: let's say we teleport a DVD (with quantum teleportation). Isn't this FTL communication? Second: ...
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three-particle quantum entanglement

So I know that two particles can be entangled in a quantum way, but is it possible that more than two particles be entangled in a quantum way? Most descriptions provide with two-particles cases, so I ...
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178 views

How would my life be different without quantum entanglement? [closed]

What would happen if for some reason quantum entanglement were suddenly turned off? By "turned off", let's say that every entangled state is immediately replaced with a separable (but still ...
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59 views

Are all particles in the universe quantum-entangled on some level?

The CMB indicates the universe was in a thermal equilibrium early on, which I understand indicates causal connection. There appears to have been some rapid expansion, and the universe now appears to ...
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1answer
47 views

Simple analytic examples of MERA

I want to understand Multi-scale Entanglement Renormalization Ansatz (MERA) with very elementary examples. So far I could find references which are mostly based on numerics. It would be a great help ...
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27 views

4 Photon Entanglement

I know that if you use SPDC (spontaneous parametric down conversion, which is the process in which a photon of a certain energy and frequency is converted into two entangled photons by being passed ...
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1answer
100 views

Measuring electron spin with multiple Stern–Gerlach apparatus at an angle

To separate the two spins of electron of a particular direction, we use Stern-Gerlach apparatuses to apply a non-uniform Magnetic field. Suppose we have two identical electrons and we know their spin ...
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107 views

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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125 views

Information, entanglement and EPR

I'm currently trying to understand why superluminal information transport is not possible. Therefore, I would like to get some help concerning the definition of information or the general setting. ...
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1answer
37 views

Can quantum states be controlled or randomized for communication using quantum entanglement?

I see "FTL" Communication with Quantum Entanglement? (which has some really awesome potential answers) Quantum entanglement as practical method of superluminal communication and, Quantum ...
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317 views

Does the entanglement depend on the basis?

Let's say, we have a composite system $A\otimes B$. We take the basis for $A$ as $|i\rangle,|j\rangle...,$ the basis for $B$ as $|\alpha\rangle,|\beta\rangle....$ Then an entangled state is a state ...
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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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62 views

Definition of a gapless spin liquid

I understand the definition of a gapped spin liquid: it's a gapped, topologically ordered spin state - i.e. there does not exist a local unitary transformation that takes it to a product state in ...
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2answers
66 views

What happens if we measure the two entangled systems of the Bell test simultaneously?

Consider the Bell state $|\psi\rangle =\frac{|00\rangle +|11\rangle}{\sqrt{2}}$. When measuring one of the individual systems, the superposition is projected onto one of the eigenstates $|00\rangle$ ...
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141 views

Simultaneous measurement for quantum entanglement

In the simple example that we measure the spin of two entangled particles, we measure one to have spin up so we know the other has spin down. If we could (theoretically) measure both particles at the ...
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1answer
71 views

Is integer quantum hall state long range entangled state or short range entangled?

I am reading about short range and long range entanglement. I know that topological insulator is short range entangled (SRE), STP state as we can disentangle it by breaking the symmetry using magnetic ...
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1answer
49 views

Are there quantum-entangled particles in nature?

Pairs of quantum entangled particles have been created in the lab, and then separated by some distance. But are there any non-manmade occurrences of quantum entanglement between distantly separated ...
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1answer
52 views

Is there a theorem which specifies the state (with energy $E$) with maximum entanglement? [closed]

Does there exist any theorem in quantum information which states that the particular state with energy $E$ is the state with maximum entanglement (or discord) among all possible state with the same ...
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2answers
166 views

Quantum probability of entangled spin-1/2 particles?

Let us say that you have two entangled spin-1/2 particles (entangled in such a away that angular momentum is conserved). Let us say particle 1 moves to the left and particle 2 to the right. We measure ...
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1answer
153 views

Can different components of a wavefunction become entangled with different systems?

Imagine a $z$-basis spin Stern Gerlach experiment where a single particle is put through the apparatus. The output is a spin state vector consisting of the sum of the two $z$-spin states. Each spin ...
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1answer
430 views

Double slit experiment and entanglement [duplicate]

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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57 views

definition of separabe/ entangled for mixed and pure states

lately I'm getting confused with the definitions for separability and entanglement. So, I'm trying to get some order into all the definitions. A pure state $|\Phi\rangle$ in some Hilbert space $H$ ...
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1answer
64 views

What does partial (non-maximum) quantum entanglement mean?

When quantum systems are entangled, they have a "grade of entanglement" which can be quantified e.g. as the entropy of entanglement. There also are states of "maximum entanglement", e.g. the Bell ...
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113 views

What is the cause of quantum entanglement? [duplicate]

I understand the idea of quantum entanglement - where what happens to one particle in one location instantly effects another particle in another location, even if separated by millions of miles. But ...
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38 views

Electron-Photon entanglement

Are the electron and photon emerging from a Compton scatter entangled? If so, what experiment can be done on one that will give information about the other?
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2answers
155 views

What is entanglement really about? [closed]

I am a beginner in this field, I am trying to understand the basics of Quantum Mechanics, I want straightforward answers to few questions on entangled photon/electron: 1- What entangled photons ...
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1answer
44 views

Representing Graphs in Entangled States [closed]

Are there ways to represent a graph G=(V,E) in an entangled state of a system of qubits ? and is there a way to forget the labels of the nodes so as to use the representation as a template to check ...
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343 views

How to understand the entanglement in a lattice fermion system?

Topological insulator is a fermion system with only short-ranged entanglement, what does the entanglement mean here? For example, the Hilbert space $V_s$ of a lattice $N$ spin-1/2 system is $V_s=V_1\...
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Spontaneous Parametric Down Conversion and the direction of the electric field component

The Spontaneous Parametric Down Conversion process is used to produce a pair of entangled photons. For this photons their electric field components are perfect adjusted by 90°. But the directions are ...
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1answer
57 views

Is it possible to create a pair of polarized, polarization-entangled photons?

Is there a light source which emits (mostly) polarization-entangled pairs of photons that have a known polarization angle, e.g. a certain angle in relation to the orientation of the source? Applying ...
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1answer
113 views

What are your views on this explanation of reincarnation using physics? [closed]

https://www.youtube.com/watch?v=GT8iVYfg9eM "Skeptical scientists keep dismissing the concept of reincarnation based on the fact that there is no need for a soul. However, one of the most skeptical ...
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Implication of non-positive tripartite information

Hayden et al 2011 showed that tripartite information is non-positive given Ryu-Takanayagi formula. (For definition of tripartite information, see for instance section 4.4 of this paper) Is there ...
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432 views

Is entanglement necessary for quantum computation?

Is entanglement necessary for quantum computation? If there was no error in the computation,superposition of states would be sufficient for quantum computation to be carried out.Is this right?
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117 views

Why is particle superposition still part of quantum mechanics? [duplicate]

After reading an article on Schrodinger's Cat, it seems that if we take the environment as an observer, that superposition cannot occur because all atomic and subatomic entities would be observed all ...
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39 views

Questions involving seperable states

I'm reading Mark Wilde's book Quantum Information Theory, and I'm stuck on two parts. I'm unable to prove: The state $\sum_{z} p_{Z}(z) \; \rho_z \; \otimes \sigma_z $, where $\rho_z$ and $\sigma_z$ ...
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How to understand the equivalence between Andreev reflection and Cooper pair injection?

It is well know that Andreev reflection dominates the subgap transport at the normal metal-superconductor interface. An incident electron can be reflected as a hole in the Nambu space, which ...
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1answer
56 views

Undergraduate quantum book treating density operators, mixed states, and entanglement [duplicate]

I'm working on a project on quantum measurement theory - in particular, relating to the quantum Zeno effect - over the summer. Right now, I'm in the process of doing background readings that'd enable ...
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1answer
63 views

Quantum entanglement and affecting the particles [duplicate]

I am trying to grasp some aspects of the quantum entanglement, but the existing resources (including some of the links here) seem a bit confusing. I am trying to find an answer to the following ...
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1answer
122 views

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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Basic quantum entanglement reference

What basic (first course for undergrads) quantum mechanics book would you recommend to read about entanglement?
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Can't quantum teleportation be superluminal some percentage of times?

I apologize if this is a really silly question. In the (textbook) quantum teleportation algorithm, in the step right after Alice has measured her system but before she has sent her classical ...
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1answer
24 views

CNOT gate with trapped ions

I'm interested in knowing the structure of a CNOT gate, in quantum computing. THe problem with that is, that I've read how the structure of a nuclear quantum computer works, but I still don't ...
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Will two entangled particles changing Synchronously while one is in a black hole and the other is not?

1.If you change the attribute of one entangled particle then the other one changes too and instantaneously. 2.The time will go slower in (or near to) a black hole compare to our normal place like on ...
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Is wavefunction collapse “global”?

I have the feeling that the premises of this question may not be coherent (so to speak), but here goes: Suppose we have a system $X$ in a quantum superposition between states $0$ and $1$, say, with ...