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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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Are identical particles always entangled even when not interacting?

Aren't the states of two identical particles always entangled even if they are not interacting? The states of two identical particles are either symmetric or antisymmetric i.e., cannot be written as ...
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Time Evolution of a Maximally Entangled State [duplicate]

My question is basically this: Does a maximally entangled state stay maximally entangled under the time evolution? Assume our Hilbert space is $\mathcal{H}_A \otimes \mathcal{H}_B$. At the time $t=...
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Entanglement of formation of the mixture of maximally entangled states

Suppose we have two spin-$S$ systems. Let $\left| \psi_{a,b} \right\rangle = \frac{1}{\sqrt{2}}(\left| a,b \right\rangle+\left| b,a \right\rangle)$ be the maximally entangled state. ($a\neq b$ and $-S\...
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High-dimensionality of multi-electron wavefunctions

My understanding is that the main difficulties in understanding superconductivity and topological insulators is related to the fact that free electrons are highly entangled and models that simplify ...
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Heisenberg picture and expectation value with position operator

I'm struggling with the use of the Hesenberg picture in Quantum Optics, where we use the position operator of a mode $\hat{x}_1$ defined as $\hat{x}_1=\frac{1}{2}(\hat{a}_1+\hat{a}_1^\dagger)$. ...
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Entangled photons entering a polarizing Beam splitter

I understand what happens to a polarization beam splitter (PBS) when a simple input is given, what happens when an entangled pair of photons is used as inputs? For example, for the state $|HH\rangle +...
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Do polarization measurements of entangled photons in any basis always produce correlated outcomes?

I am looking to confirm or clarify my understanding of a measurement on an polarization entangled pair of photons. I am considering an entangled pair in the state |ϕ+⟩ =1√2(|HH⟩+|VV⟩) (positively ...
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Entangled photon absorption redshift/blueshift scattering

I have read these questions and answers and none answered my question. What happens when one of the photons in entangled state gets destroyed? Does measuring destroy entanglement Information and ...
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Entangled photon triplet

I have read these questions and answers, and it made me curious How does measurement affect multi-particle entangled particles? How do particles become entangled? What is quantum entanglement? Two ...
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Status of entanglement/black hole entropy in quantum field theory

It used to be said that in QFT, black hole and entanglement entropy is overcounted because entropy turns out to depend on volume, even if we somehow eliminate infinities. Does this assessment still ...
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108 views

How are joint measurements of quantum states realized experimentally?

I have a question regarding the experimental implementation of joint measurements of quantum states. While I understand for example the teleportation protocol using Bell states, something that still ...
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Quantum solution to the two-army problem?

The two-army problem can be described as follows: Two blue armes is separated by the white army, they can win the battle only if they attack together. However, the messenger who send the attack ...
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Superposition of polarized photon

I understand that a $+45^\circ$ polarized photon is a superposition of $0^\circ$ (vertical) and $90^\circ$ (horizontal): $|\!+\!45\rangle = 0.707 (|H\rangle + |V\rangle)$. So measuring the ...
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How to properly calculate off-diagonal terms in covariance matrix for entangled Gaussian state?

I would like to ask how to properly calculate the off-diagonal terms in covariance matrix for the entangled Gaussian state? E.g. from https://arxiv.org/abs/0810.0534v1 we have a coherent Gaussian ...
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Unitary transformation from pure unentangled state to pure entangled state

I believe that for any state $|\Psi\rangle$, that is unentangled, and for any state $|\Phi\rangle$, of the same dimension that is entangled, there is a unitary operator $\hat{U}$ such that $\hat{U}|\...
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Can urea crystals be used to generate pairs of entangled photons?

According to this link https://patents.justia.com/patent/4639923, urea crystals can be used as optical parametric oscillators. The parametric oscillator uses a nonlinear crystal to convert the pump ...
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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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Understanding entanglement entropy in the transverse field Ising model

I'm working on a project studying the transverse field Ising model in 1D with periodic boundary conditions, given by $$H = - J \sum_{i=1}^{N} \sigma^z_i \sigma^z_{i+1} - h \sum_{i=1}^N \sigma^x_i$$ I ...
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Wigner function in quantum teleportation

I'm starting to manipulate Wigner function and I'm studying the Wigner function approach in Quantum Teleportation. My reference for this is page 29-30 of Braunstein and Van Loock "Quantum ...
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How to describe time dependence piece of a stationary state with average phase

I am reading this paper on the synchronization of atomic clocks via entanglement (https://arxiv.org/pdf/quant-ph/0004105.pdf) and can't figure out how they are using $\Omega = (E_{1} - E_{o})/\hbar$ ...
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What is the minimum number of separable pure states needed to decompose arbitrary separable states?

Consider a separable state $\rho$ living in a tensor product space $\mathcal H\otimes\mathcal H'$, with $\mathcal H$ and $\mathcal H'$ of dimensions $D$ and $D'$, respectively. If $\rho$ is separable, ...
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1answer
167 views

Why in the definition of GHZ state only the $M>2$ case is considered?

I have a basic question about the definition of the Greenberger–Horne–Zeilinger state , which is defined as the maximally entangled state. Why is it only considered applicable for subsystems $M > 2$...
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How do entangled matter condensates fall?

Is there any experimental measurement of how highly entangled matter states fall (or highly entangled photons curve) in a gravity well? I've found some preliminary experimental setups in this paper ...
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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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If a state can be efficiently represented by a Projected Entangled Pair State (PEPS), can we prepare it physically?

If we can use PEPS (Projected Entangled Pair State) to represent a many body quantum state, can we generate it by a quantum computer? As far as I can understand, PEPS is dual to a quantum computer ...
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Question on Eigenstate thermalization hypothesis

My understanding of a system that satisfies the eigenstate thermalization hypothesis (ETH) is the following. If we consider a local operator, $O_i$ we can relate its expectation value with respect to ...
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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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Entangling two quantum systems that are separated by a distance

If two quantum systems are entangled their measurements become correlated, even if they are separated by a distance. But what if one has two different quantum systems at hand, initially un-entangled ...
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Can the entanglement entropy of a ground state scale extensively?

To my knowledge, entanglement entropy (EE) for the ground state of a many-body system scales subextensively, that is: \begin{equation}\lim_{\text{Vol}_A \to \infty} \frac{S_A}{\text{Vol}_A}\to 0.\end{...
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Does time emerge from entanglement?

I stumbled upon the hypothesis that time emerges from quantum mechanics as long as the observer is part of the system. That is, the evolution of an entangled state can serve as a clock for an observer ...
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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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When two particles are maximally entangled, can we decompose the combined system arbitrarily?

This will sound like a philosophical question (i.e. a question with no actual theoretical content), but I dont intend it as such. Admittedly, my question is based on a very vague intuition. Also note,...
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Quantum Communication - Tx/Rx terminolgy?

When talking about Quantum Communication vs. Classical Communication data is passed via quantum entanglement; data doesn't traverse the space between the involved particles. Is one particle "...
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Tensor product states in QM

In QM, we use tensor products to construct the vector space of the states of a multi-particle system - but that construction doesn’t seem to have a counterpart in classical mechanics. In QM, it seems ...
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Is a GPU accelerated Quantum computer simulator publishable research?

I have built a GPU accelerated quantum computer simulator that is quicker then libquantum and the IBM QISkit simumators. Is the work done on this (methods, archetecture) publishable?
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Entanglement in a uniform magnetic field

Suppose we throw only one particle (1) with spin-1/2 into a uniform magnetic field while letting free the other entangled particle (2). The state of the particle-2 will not be affected and this is a ...
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Intuition on quantum teleportation

I'm trying to understand quantum teleportation and I was wondering if anyone could provide an intuition about it. I have seen the derivation but it still bugs me. You start with an entangled pair of ...
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Theoretical approach of the quantum CNOT gate

Let's $ |\psi \rangle $ be $ \sqrt{1} \begin{pmatrix} \frac{2}{8} \\\ \frac{6}{8} \end{pmatrix} $, $ |\phi \rangle $ $ = \sqrt{1} \begin{pmatrix} \frac{3}{4} \\\ \frac{1}{4} \end{pmatrix} $, and $ |...
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Quantum Entanglement, connected or just in tune? [duplicate]

I read a few of the questions suggested to be similar, but I didn't see what I am looking for. Please feel free to point me in the right direction if I just missed it... (there are quite a few). ...
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What are the “parts” of separable quantum states?

Of course I could only speak of whole states and banish the word "parts". Mathematics enables some quantum states to be separated into partial states. When the whole state has finite dimensions, the ...
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Quantum computing: CNOT gate

A CNOT gate can be written as follow: $$\begin{pmatrix}1 & 0 & 0 & 0 \\\ 0 & 1 & 0 & 0 \\\ 0 & 0 & 0 & 1 \\\ 0 & 0 & 1 & 0 \end{pmatrix}$$ So using ...
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How does entanglement work for states where number of particles is undefined

Entanglement and separability are often described in terms of tensor products of particle states. For example the Alice/Bob two qubit example. Many states do not possess a definite number of ...
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219 views

Understanding the GHZ game

I am trying to understand the basics of the GHZ nonlocal game in quantum information theory. I have searched for all the info i could find, thought i understood, but still face some basic ...
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1answer
109 views

Double-slit experiment on cats makes inconsistency?

According to Wave-Particle Duality, in a normal double-slit experiment, the quantum object behaves as wave and many stripes are displayed on the screen. But if we measure which way the quantum object ...
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How can one understand entanglement when there is only a single particle?

As per my knowledge, at least 2 particles are needed to show entanglement in the context of some property. But nowadays, mode entanglement is a well known phenomena which says that a single particle (...
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Using entangled particles to transfer energy or a force?

My question is a two part question: When two particles that have mass are entangled (e.g. two electrons) are their Higgs field(s)/mass also entangled? If mass is an entanglable property of particles ...
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Physical intuition of partial trace in a GHZ state [closed]

I'm having trouble understanding the physical information one might extract from partial traces, by interpreting the partial trace of a qubit as if the qubit was averaged out of the system. For ...
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Can we always find a Hilbert space corresponding to a region of spacetime?

In defining entanglement entropy in field theories we take a region A in spacetime. Now if $\mathcal{H}$ is the Hilbert space of the field theory we assume that we can decompose this Hilbert space ...
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1answer
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Using QED to calculate the the success probability of sending a pair of entangled electrons

Some procedures of quantum information technologies, such as quantum teleportation, require two parties to share a pair of entangled particles, i.e., each party has access to one of the particles, and ...
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$mn$-dim Hilbert space vs product of $m$ and $n$ Hilbert spaces

Assume one has a Hilbert space $\mathcal{H}_K$ of dimension $K=mn$. Associated to it, there exists a set of all possible quantum transformations $\mathcal{E}$. Of those, the most important are, of ...