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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Limiting factors in traditional microscopy

I have been researching Entanglement-Enhanced Microscopy, and the overall breakthrough seems to be obtaining a resolution of $1/N$ as opposed to $1/\sqrt N$. This led me to ask what the limiting ...
murtadee hughes's user avatar
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Does Bell’s theorem rule out changing hidden variables?

In the EPR experiment, it is said that there are predictions that are made if there are hidden variables determined by something locally in each particle that results in a correlation in entanglement. ...
Alejandro's user avatar
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How do physicists talk about spin of individual particles when the universe is massively entangled?

The following two things seem to be true: (1) The universe is massively entangled because the wave function that describes the entire universe has measure 1 of being entangled. Further, given how ...
zzz's user avatar
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Why does my Hermitian matrix $R$, which is used to calculate the concurrence, sometimes becomes non-Hermitian? [closed]

I have a $4\times 4$ Hermitian density matrix called $A_{x}$ whose elements are labelled $a_{ij}$ $(i,j = 1, 2, 3, 4)$. (See definitions in the code below.) The $a_{ij}$'s are functions of two ...
Quantum Kid's user avatar
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What is the percentage of entangled content (matter and radiation) in the universe after big bang? And what are the implications?

I searched for entangled matter in cosmological context but didn't find anything that actually answers my question. Big bang nucleosynthesis is actually a series of chain reactions that produces a ...
jim andr's user avatar
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Computing Fubini-Study expectation values over $\mathbb{C}P^n$

In finite-dimensional textbook quantum mechanics, we postulate that states of our system are rays in a Hilbert space $\mathcal{H}$ with dimension $\dim{\mathcal{H}} = n+1$ where $n \in \mathbb{N}$, ...
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Partial trace on a two-mode continuous-variable quantum state

I have the following continuous-variable entangled state $$ \left|\psi\right\rangle_{1,2}= \int_{-\infty}^{+\infty} dq_{1} dq_{2}~\psi(q_{1}) f_{G}(q_{2})e^{\frac{i}{2} q_{1}q_{2}}\left|q_{1}\right\...
Julio Abraham Mendoza Fierro's user avatar
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Does the no signalling theorem in quantum mechanics beg the question?

I had always thought similarly and then came across a paper here that argues this. The abstract is as follows: Many authors state that quantum nonlocality could not involve any controllable ...
Ronald 's user avatar
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Is quantum entanglement the only example in physics where consistent correlations happen without a cause? [duplicate]

So as far as I am aware, there is currently no cause that explains how exactly two entangled particles remain correlated even when separated at a large distance. If there is a cause, it is presumed to ...
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How do you determine if an Hamiltonian allows entanglement and when?

Sorry for the vague setup, but I'm a noob and I'm trying to understand, so please be patient. Let's say that I have a tight-binding, 2D, square lattice Hamiltonian $$ H = H_t + H_{interaction} + H_{\...
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Measuring Incompatible observables simultaneously of an entangled electron [duplicate]

Given that a pair of electrons are in the state $$\psi =\frac{ {|00}\rangle \pm {|11}\rangle }{\sqrt{2}}$$ (in the the spin-$x$ eigenbasis) . If we measure the spin along $x$ axis of one of the ...
veke's user avatar
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What are the implications of the EPR bridge information metric being invariant under all conditions, including distance in this universe?

What if the reason why instantaneous state information is able be transmitted between entangled particles through an EPR bridge is that the metric that this is conveyed in is invariant under all ...
Odysseus Ithaca's user avatar
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Decoherence model of two qubits interacting with correlated multimode fields - open quantum system

I read paper on open quantum system, that talk about non-Markovian process and memory effects. they described the system as a generic decoherence model of two qubits interacting with correlated ...
Yohay Halfon's user avatar
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What does doubly-entangled $W$-like state do with three-particle setup?

First, is entanglement of three particles in $W$-like state deliberately possible (and not by chance)? Second, is the following statement correct? In the doubly entangled $W$ state, represented as $$ |...
K Ivanov's user avatar
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Does it make sense to talk about individual energies of interacting quantum particles?

Does it make any sense to talk about energy of any one particle in an interacting system? For example if we talk about a system of two coupled quantum harmonic oscillators of same mass and frequency, ...
HypnoticZebra's user avatar
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Mermin's EPR paradox explanation [closed]

I am reading N. D. Mermin, Bringing home the atomic world: Quantum mysteries for anybody . The main part of the article is pretty clear to me. But I am not sure how quantum mechanics described in ...
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Does local realism imply entangled photons are equal (or opposite)?

I'm watching a video about Bell's inequality and how there can be no local hidden variables. They explain it using photons and whether they pass through a polarizer or not when they're oriented at ...
Juan's user avatar
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Entangled particles and the Andromeda paradox experiment

I know there are other questions linking the two subjects. I am not asking about an explanation, rather I am curious whether an experiment would be possible. To explain the experiment let's start with ...
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Why we cannot transfer information using a spin entangled singlet? [duplicate]

In QM and QE effects an entangled particle pair is called also a singlet with some properties of the two particles like spin, non-locally correlated. However, there is no transfer of information ...
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What happens to entangled particles at a Black Hole? [duplicate]

I am probably going to ask this wrong, so please don't flame me. I am not a scientist or student.... If an entangled particle enters an event horizon but has not reached the singularity, can we still ...
Rick's user avatar
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How much entanglement does each quasiparticle carry?

The dynamics of entanglement entropy $S$ out of equilibrium can be understood in some regimes from the point of view of the quasiparticle picture: an excited state acts as a source of pairs of ...
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Is it possible to conduct quantum teleportation with a larger than necessary e-dit and preserve entanglement?

Suppose you have an e-bit between qubits A and B. You want to transfer the state of qubit Q to B. You can utilize this e-bit to perform a quantum teleportation to achieve this. Now instead suppose ...
Logan J. Fisher's user avatar
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Can you split maximally entangled qudits into maximally entangled lower-dimensional qudits?

Suppose you have qudits A and B. They are each of some large dimensionality d and are maximally entangled with each other. Is it possible, by some protocol, to split these two qudits into C, D, E, &...
Logan J. Fisher's user avatar
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How to determine parameters such that the state $|\psi\rangle=\frac1{\sqrt2}|+\rangle|+\rangle+a|+\rangle|x+\rangle+b|-\rangle|-\rangle$ is separable?

Suppose that two spin-1/2 are in the state: $$ |\psi \rangle = \frac{1}{\sqrt{2}} |+\rangle|+\rangle + a|+\rangle|x+\rangle + b|-\rangle|-\rangle $$ and we want to find values for a & b such that ...
ilra's user avatar
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The Formula For Entanglement Entropy of an Evaporating Black Hole

I am trying to find a proof for the formula for entanglement entropy of an evaporating Black Hole. It is introduced and used in many papers such as The entropy of Hawking radiation, by Ahmed Almheiri, ...
TheFyziker's user avatar
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1 answer
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How can resolution of particle entanglement be detected, and why can't it be faster than light communication?

Sorry for the length, but this is driving me crazy. And yes, there are other questions on this issue and I have reviewed them, but I cannot see the answer stated simply. What is different about my ...
RalphBerger's user avatar
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1 answer
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Understanding operator product of three mixed states with three projector operators

I am recently studying the triangle scenario in the context of Bell nonlocality (for reference, see for instance this article). In it, we have three parties, commonly referred to as Alice, Bob and ...
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Path Integrals for entangled states

Is there a way of characterizing entanglement between states in a path integral formalism? If so, does this shed some light on the apparently non-local effects of quantum mechanics?
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Decoherence time of quarks

I have been reading papers on using top quark's use as a probe for new physics using quantum information theoretic observables such as concurrence. One of the reasons they provide for using a top ...
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Proving that a positive partial transpose (PPT) state is non-distillable

I am attempting to prove the following statement: A positive partial transpose (PPT) state cannot be distilled. I would like to do so using the following facts: Let $\rho$ represent a bipartite ...
oki-dogz's user avatar
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1 answer
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A cloning question involving quantum entanglement

Firstly, I am not exactly an expert at this, and I have only just found out about quantum entanglement. So from what I know, quantum entanglement allows information from one atom to be "copied&...
Rowan Murtagh's user avatar
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3 answers
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Entanglement question relativity [closed]

Assume a particle's spin is measured along the vertical axis at time t=0 and position x=2. An entangled partner particle is measured along the vertical axis at time t=0.5 and position x=0 (also along ...
Nikolai riber skånstrøm's user avatar
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How do I convert this separable state into a product state?

I know two particles in a Bell state cannot be written as a product state as they are entangled. But what if I had a classically correlated state$$\rho = \frac{1}{2}(|11\rangle\langle 11| + |00\rangle\...
DJames's user avatar
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How does squeezed multimode light, where the modes are entangled, behave in a beamsplitter?

I understand how to work with and describe squeezed single modes going through a beamsplitter, and can conceptually talk about what's happening. If I now take a source of squeezed light that has ...
compp's user avatar
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Optimal pure state decomposition of bipartite mixed states [closed]

Suppose I have a 2-qubit mixed state given by $\rho$ whose concurrence is $C$. I am interested in finding the optimal pure state decomposition of $\rho=\sum_{i=1}^4 p_i|\psi_i\rangle\langle\psi_i|$ ...
Aniket's user avatar
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3 answers
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Simplest experiment to see quantum interference of $|HH \rangle + |VV \rangle $?

What is the simplest experiment that I can perform to see interference of $|HH \rangle + |VV \rangle $, assuming this is an entangled state of two photons in two different polarizations? Ideally I ...
Steven Sagona's user avatar
1 vote
0 answers
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SPDC entangled photons and orbital angular momentum?

I know that spontaneous parametric down conversion (SPDC) produces entangled photons in the orbital angular momentum (OAM), i.e., for a pump beam with zero OAM, $ |\psi \rangle = | 0 0 \rangle + | 1 -...
MementoMori's user avatar
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Constructing wavefunction for a mixed state

This question is somehow the reverse of another question. If a quantum system $S$ is in a pure state, then we can find a wavefunction that describes $S$. This wavefunction is unique up to a phase ...
Riemann's user avatar
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Entanglement island distance = quantum width of BH horizon?

In this recent paper, Bousso and Penington (B&P) finds that the protrusion distance outside the horizon of an entanglement island from a 4D Schwarzschild black hole is $\sqrt {l_P r_{hor}}$, where ...
Mr Anderson's user avatar
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3 votes
2 answers
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Are electrons in higher energy orbits less entangled with the nucleus?

I understand that an electron in orbit is technically entangled with the nucleus. Is an electron with higher energy (further away from the nucleus) less entangled with the nucleus? Does a free ...
Chinmay Nagarkar's user avatar
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4 answers
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Quantum entanglement and speed of transmitting information [closed]

Imagine Alice and Bob have two pairs of entangled particles, pair A, and pair B. Imagine they have agreed beforehand that pair A measurement preceding pair B measurement constitutes a bit with value 1 ...
Abhishek Nair's user avatar
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2 answers
145 views

Quantum entanglement and relativity

I'm having trouble understanding the interplay between special relativity (more specifically the relativity of simultaneity) and quantum entanglement. Imagine there are two observers, as shown in the ...
Nikolai riber skånstrøm's user avatar
2 votes
0 answers
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A Hamiltonian acts simply on each state in some subspace. Can it be identified with a single simple operator on the subspace?

This is a simplified version of a recent question I asked. My hope is that this simplified version will be easier to tackle. The motivation behind both of these questions is roughly to ask "Given ...
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If my time evolution operator can't change my entanglement, can I find a simpler time evolution?

Consider a Hamiltonian $H$ on some spin chain of length $L$. Suppose we have a subset of $n$ eigenstates $\{|\psi_i\rangle \}$ of $H$ obeying the following special condition. First, a couple quick ...
user196574's user avatar
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3 votes
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Two states have the same Schmidt coefficients across every bipartition. Can they be mapped to each other by a product of single-site unitaries?

I have two states, $|\psi\rangle$ and $|\phi\rangle$. I have in mind that they live on a length $L$ spin chain with finite local Hilbert space dimension. I know that for every Schmidt decomposition ...
user196574's user avatar
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1 vote
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Classical limit of quantum mechanics from decoherence or diminishing hbar?

Two pictures regarding the classical limit of quantum mechanics. One says in path integral take hbar to zero then the paths constructively interference near the classical path and the paths deviate ...
user74750's user avatar
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Benefit of using entangled photons over classically correlated source for ghost imaging

I have found a paper(See this) which talks about the comparison of classically correlated source and an entangled photon source (generated by Spontaneous Parametric Down Conversion)for ghost imaging. ...
QuantumOscillator's user avatar
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Non-entangled non-classical quantum correlations?

Are there any list or classification of non-entangled quantum correlations in quantum states for multiparty (possible high dimensional) quantum states (included infinite-dimensional case)? I mean, a ...
riemannium's user avatar
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Can entanglement witnesses on GHZ states with $n > 2$ violate the non-communication theorem?

In experiments involving entangled photons, measuring entanglement in systems with more than two particles ($n > 2$) often employs one photon as a herald to distinguish signal photons from noise. ...
Scott Stults's user avatar
1 vote
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Eigenvalues of truncated correlation matrix

Take a Fermionic gapped 1-D lattice Hamiltonian $H=\sum_{ij}t_{ij}c^\dagger_ic_j$ with periodic boundary as an example, and we bipartite it into two subsystems $A$ and $B$, and the eigenvalues of the ...
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