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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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Alignment of axes of measuring devices in a quantum entanglement experiment

Concerning quantum entanglement Wikipedia says: Measurements of physical properties such as position, momentum, spin, and polarization, performed on entangled particles are found to be ...
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Standard form of representing and entangled state [on hold]

from where can I learn how to represent entangled states in their standard form?
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Difference between an entangled pair of photon and two magnets in a box? [duplicate]

I try to understand quantum entanglement and especially what it’s called « Action at a distance » from my understanding, if you have a pair of entangled photon, after measuring the polarization of ...
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Is the Schmidt basis the one minimizing entanglement?

I know, that for a compound system $ |\psi \rangle_{AB} $ we can find the Schmidt basis, which is an unique one. Is it at the same time the basis, in which the two subsystems are minimally entangled? ...
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What could be the possible physical setup to make BEC of composite bosons? [on hold]

What kind of physical setup we can use to make Bose-Einstein condensation of Composite bosons?
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Entanglement Swapping of Werner states

I am provided with two Werner states \begin{equation*} \rho=F|\phi^+><\phi^+|+\frac{1-F}{3}(|\phi^-><\phi^-|+|\psi^+><\psi^+|+|\psi^+><\psi^+|) \end{equation*} or ...
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Why can't we communicate with velocity greater than light though entanglement of particles is a reality? [duplicate]

Suppose we have two entangled particles-one electron and one proton-both produced by radioactivity. Now suppose they are separately caged in two boxes in which they can't interact with any other ...
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Can post-selecting on the screen in the Delayed Choice Quantum Eraser experiment be used to predict the quantum-eraser measurement results?

I'm curious about QM and spent the last 3 days thinking about Delayed Choice Quantum Eraser (DCQE) experiment, but I couldn't solve this issue: Assume we do the DCQE experiment so that for the whole ...
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Quantum eraser without the quantum eraser

I've recently watched PBS SpaceTime's video about the quantum eraser. In it, Matt describes a kind of crystal that splits particles into pairs and entangles them. The entangled particles are then ...
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Entanglement measures and Asymptotic continuity

I'm finishing my master studies in Theoretical Physics and my thesis is being about entanglement measures. I've read several papers in which all kind of properties that one would desire to have in a ...
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What's the meaning of distant measuring?

this is the context: Einstein, Podolsky, and Rosen concluded that there are two possibilities in the case of the spinning particles. Either (a) there is some mysterious, nonlocal interaction that ...
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How many tensor product terms are necessary to express a separable state? [duplicate]

Wikipedia (https://en.wikipedia.org/wiki/Separable_state) defines a separable state, as a state $\rho$ which can be written as: $ \rho = \sum_{k=1}^l p_k \rho_1^k \otimes \rho_2^k $ where $\sum_{k=1}...
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Can Quantum Entangled particles convey information faster than speed of light? [duplicate]

Can Quantum Entangled particles convey information faster than speed of light. If they don't what was wrong with John Bells experiment?
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Is the Proof of Gisin's Theorem Wrong?

I have been trying to understand Gisin's paper, Bell's inequality holds for all non-product states. As I've worked through the proof he provides for his theorem, I've run into two things that simply ...
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Superoperator cannot increase relative entropy

So I have to show that a superoperator $\$$ cannot increase relative entropy using the monotonicity of relative entropy: $$S(\rho_A || \sigma_A) \leq S(\rho_{AB} || \sigma_{AB}).$$ What I have to ...
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How to identify whether a quantum state is entangled or separable if you can measure it only in one basis?

Suppose you have two qubits and don't know whether they're in an entangled state $ \frac{1}{\sqrt{2}}\left(|0,0\rangle + |1,1\rangle\right)$ or in an equal mixture of states $ |0,0\rangle $ and $ |1,1\...
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If quantum entanglement isn't a physical thing how does it makes quantum teleportation work? [duplicate]

I read about superposition and correlation between entangled particles and there is no physical communication between them, but obviously quantum teleportation uses this correlation to send something ...
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How do I apply no signaling condition for the given Quantum Adder problem

The Unitary transformation for the Imperfect Quantum Adder problem is such: Both the states belong to two Hilbert Spaces and we are trying to add both states to one system using Ancillary qubit. I ...
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How does weak measurement affect quantum state?

I'm trying to understand how to describe the quantum state after weak measurement using these two toy examples. Hopefully, these simple examples and your answer will help others who want to learn ...
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Representation of Translation Invariant Matrix Product States

Consider a matrix product state on $\mathbb{C}^{d N}$: $$ \Psi = \sum_{\sigma_1,...\sigma_N} A_1(\sigma_1) ... A_N(\sigma_N) |\sigma_1 ... \sigma_N \rangle \quad \quad (\text{OBC MPS}) $$ with some ...
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Does the EPR paradox assume that entangled particles leave each other's light cones, or not?

So I was reading this post by Ethan Siegel, which introduces a recent talk by Lee Smolin. In the article, Siegel outlines the EPR paradox (or something like it) and mentions that it is based on the ...
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Quantum Coherences of a Subsystem

I am reading some stuff on quantum mechanics and have seen references to a subsystem B (where A and B are both subsystems in the system) which has quantum coherences which can be selected. I was ...
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Are there theories or experiments involving multi variable particles?

Every hidden variable/entanglement experiment I’ve ever heard described involves ONLY one variable of either polarization or spin. Therefore Venn calculations backed by diagrams highlight the ...
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Other than polarization what hidden variables have been applied to pairs of particles to correlate them?

Are there examples where correlated pairs where given certain specific variables or multiple variables in an attempt to produce the predictions of quantum mechanics?
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Norm Closure of Set of MPS

Consider the set $MPS$ of matrix product states in the thermodynamic limit, with translation invariance. Then $MPS$ is $w^\ast$-dense in the set of translation invarian states. But what is $ \...
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Entanglement breaking quantum channels

An entanglement breaking quantum channel is defined as one where $\sigma_{AB}=(\Phi_A\otimes I_B)(\rho_{AB})$ is separable, even for entangled inputs $\rho_{AB}$. Of course, if the input $\rho_{AB}$ ...
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A case where entanglement leads to correlation in decay time

Half-lives of unstable or metastable states are typically known, but specific decay times are inherently uncertain. On the other hand, quantum entanglement leads to correlations between inherently ...
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Decomposition of the maximally entangled states

We know that the set of symmetric bipartite pure states is spanned by $S=\{|\phi\rangle^{\otimes 2},|\phi\rangle \in \mathbb{C}^d\}$. I want to know if the maximally entangled state $|\psi\rangle = \...
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What is frequency entanglement?

If frequency (or energy) is regarded as a quantum property, can one generate a pair of photons with frequency entanglement? What would be the uses of this type of entangelment in say, sensing? How ...
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What would happen if the opposite complementary variables of two entangled particles were measured at the same time?

Many explanations about the uncertainty principle and its related EPR paradox state that it is impossible to measure opposite complementary variables on different entangled particles; for example, ...
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Quantum Computation - Finding joint state given partial properties of two pairs of qubits [closed]

I have a problem I need to figure out how to solve for an exam in a few days and I'm struggling to find any advice online I need to find the joint state of two pairs of entangled qubits following the ...
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Storage of entangled particles

I have been trying to find the answer to these questions on the net but have had no luck. Can entangled particles be stored? Can an entangled particle be repeatedly measured?
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Partial Transpose in Gapped Time-reversal Symmetric Spin Chains

Suppose you have a one-dimensional quantum spin system with on-site Hilbert spaces $\mathcal{S}$. Suppose there is an anti-unitary, anti-linear operator $C$ on $\mathcal{S}$ inducing an anti-linear, ...
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Scan Quantum mechanics: Status of current research

I recently stumbled on a new interpretation of Quantum mechanics, called Scan Quantum Mechanics, given by Beatriz Gato-Rivera. She suggests a quantity called quantum inertia, which divides the ...
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What is the meaning of this operator?

In interferometry with coherent light, the final output is differenced detectors. That is, $\left<N\right> = \left<N_1\right> - \left<N_2\right>$ where $N_i$ is the number operator ...
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Critical parameter for 1D quantum system corresponding to $T_c$ of 2D Classical model

Utilizing the fact that there is a correspondence between a $d$ dimensional quantum system and a $d+1$ dimensional classical system (c.f. Trotter Decomposition), my question regards what the critical ...
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Physical Interpretation of the Spectrum of MPS Transfer Matrices

Take an injective, translation invariant MPS with transfer matrix $E = \sum_\sigma \overline{A^\sigma} \otimes A^\sigma$ (i am using the terminology of https://arxiv.org/abs/quant-ph/0410227 , eq. (6))...
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Intuition behind quantum CNOT gate applied to a pair of electrons [duplicate]

I'm looking for some intuition behind how a cNOT gate works. I think I understand the mathematics; but, I'm having trouble imagining how two electrons would interact to produce the predicted result. ...
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How do you know when two objects are so called entangled?

I’m not asking how would you entangle two objects. I want to know how would you know they are entangled?
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Can the reduced state of a mixed entangled state be pure?

For an entangled pure state, the Schmidt decomposition is such that there are at least two non-zero Schmidt coefficients. Tracing out one subsystem implies that the other subsystem is mixed. ...
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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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Say you run qubit $A = (|0⟩ + |1⟩) / √2$ and qubit $B = |0⟩$ through a CNOT gate. What is the state of qubit $B$ afterwards?

I am new to the weeds of quantum computing and this question is probably pretty elementary. Say you run qubit A = (|0⟩ + |1⟩) / √2 and qubit B = |0⟩ through a CNOT gate. What is the state of qubit B ...
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Have researchers managed to “reverse time”? If so, what does that mean for physics?

According to press releases, researchers have reversed time in a quantum computer and violated the second law of thermodynamics. What does that mean for physics? Will it allow time travel? Further ...
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Basis ambiguity for bipartite entanglement

I am reading Decoherence, einselection, and the quantum origins of the classical from Wojciech Hubert Zurek And he says at some point that for a three partite quantum system there is no basis ...
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Are the electrons in the Delft University experiment really entangled?

I have been studying the Loophole-free Bell test at the Delft University. They were using the "Entanglement By Accident" method. When they trigger an electron, the electron falls back in one of two ...
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How to search Feynman diagrams for entanglement [closed]

This question is partly about physics, partly about love -- but I don't believe there's a Stack Exchange for the later :) My girlfriend is a PhD physicist who finds the notion of entanglement very ...
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Does a polarizer affect both entangled photons or only one?

Suppose you have two polarization-entangled photons A and B in the following state: \begin{equation} \Phi=\frac{1}{\sqrt{2}}\bigl(\left|H_{A},H_{B}\right\rangle + \left| V_{A},V_{B}\right\rangle\bigr)...
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Do Chern Insulators (QAHE) have topological order (long-range quantum entanglement)?

I know IQHE is a example having "invertible" topological order from Professor Wen's definition. And Topological Insulators is SRE because of necessary of underlying symmetry protection. After that, ...
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The maximally mixed state is at the center of all quantum states

The set of quantum states $\rho$ in $d$ dimensions is the set of positive semidefinite operators living in a Hilbert space of dimension $d$. Let us denote this set by $\text{Pos}(X)$ and note that ...
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How does a photon released from particle A interacting with particle B, entangle them?

What does a photon carry from its parent particle that when it interacts with another particle, it entangles both the particles?