# 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.

1,119 questions
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### Simulating the evolution of many-boson states

My task is to simulate the scheme presented in this paper: https://journals.aps.org/pra/abstract/10.1103/PhysRevA.77.062316. In this question: Creating an operator for a polarizing beam splitter, I ...
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### Covariance matrix and displacement after homodyne detection on three-mode state

I'm provided with the covariance matrix of a three-mode cluster state (a state which is obtained by entangling three momentum squeezed states). I want to see what happens to this state when I measure ...
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### Physical meaning of parametric down conversion of photon

I would like to understand what is the physical processes occurring in the particle picture when parametric down conversion of photon happens. The description in Wikipedia states: "A nonlinear ...
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### Entanglement entropy calculation

I have been trying to understand this paper: Susskind. “Black Hole Entropy in Canonical Quantum Gravity and Superstring Theory.” [1402.1128] Long Short-Term Memory Based Recurrent Neural Network ...
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### Is BEC the same as entanglement?

I understand that Bose Einstein condensate is: A Bose–Einstein condensate (BEC) is a state of matter of a dilute gas of bosons cooled to temperatures very close to absolute zero. Under such ...
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### Quantum Computing, and if a Q-bit can be entangled and in superposition at the same time

I was wondering if a Q-bits can be in both entangled and in superposition at the same time?
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### If quantum entanglement is not an active link between particles, then how did China transmit data via Earth-to-space quantum entanglement? [duplicate]

So based on this thread : Why is quantum entanglement considered to be an active link between particles? which was asked 7 years ago, the answer says "Entanglement is being presented as an "...
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### Can someone explain in a simple manner that How can we use Quantum entanglement to transfer data instantly when we seperate photons? [duplicate]

So I'm an IT engineer and i just watched a video about Quantum entanglement, that somehow when we split the entangled photons, any change happening to one of them will be reflected to the other one ...
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### Why can't we increase quantum entanglement via LOCC?

Why must every measure of entanglement satisfy the crucial property that its expected value is non-increasing under LOCC?
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### How does a unitary operator acts on an entangled $|\psi\rangle$? [duplicate]

If there is: $$U = \sum_{x,y \in \mathbb{Z}_2} |x \dot{+} y\rangle |y\rangle \langle x| \langle y|$$ acting over $|\psi\rangle$ which can be $|00\rangle, |01\rangle, |10\rangle, |11\rangle$, does ...
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### A telegram from Mars

Say, people fly to Mars, get in trouble, and want to send us a SOS signal. The average distance is 225 Gm, so they must wait 25 minutes to hear our response at the speed of light. This may just be too ...
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### Entangled qubits measurement

I have two entangled qubits. I measure one of the qubits and get a 1. Am I correct in saying that the second qubit instantaneously collapsed to a correlated state, even before I measured it? Or does ...
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### Is there a way to determine if one qubit of an EPR pair has collapsed after the other was measured?

My friend on the other side of the universe and I share the respective qubits of 2 EPR pairs. My friend measures one of the qubits, so one of my qubits will collapse. Must I measure this collapsed ...
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### Why does quantum entanglement break?

Why does quantum entanglement break when the corresponding particles are intefered with? Is there possibly any way to actualy use it, such as in interstellar communication?
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### How do we know quantum entanglement really happens? [duplicate]

Quantum entanglement says that we can entangle two particles with an opposite property, separate them, and that they exist in an indeterminate state until we observe one of them. eg. If we create a ...
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### What do physicists mean when they say QM proves randomness?

Some physicists like Michio Kaku has said that the physics has proven randomness. Even some of my friends(they're not physicists) cite the Delayed Choice Quantum Eraser experiment and entanglement to ...
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### Types of entanglement not due to conservation principles

In a comment on Mechanism of quantum entanglement; proof of quantumness, Emilio Pisanty stated, There's many types of entanglement, and only a few can be traced to any sort of conservation law. ...
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### On the entanglement of photons polarization

I am trying to make my perception evolve to include non-locality, and this idea is one of the last that I want to invalidate in order to get there. When we emit two entangled photons and test their ...
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### Are there Bell test experiments that don't require coincidence monitor?

CHSH (2-channel) for instance doesn't count for a case where all 4 channels didn't detect anything (simultaneously) at some point in time. As I understand, such all-absence shouldn't happen/matter at ...
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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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### Quantum Physics - decorrelate 2 particles initially entangled

I am studying the entanglement in quantum physics, especially the Aspect's experience where 2 photons initially correlated keep this correlation through the measure of their polarity. The Wikipedia ...
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### Are Bi-photons and Fock States (with $N=2$) the same?

I've been researching about quantum states of light, and I came across with both terms. For what I understand of both, I think they are the same (entangled individual photons with same position and ...