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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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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How does the trace acts over one of the two entangled qubits? [duplicate]

If $|\psi\rangle$ is entangled, i.e, is in the subspace spanned by the states $|00\rangle, |01\rangle, |10\rangle, |11\rangle$ how does the partial trace operates on the density operator $|\psi\rangle\...
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Can we use entangled black holes to form wormholes?

If any object can be made black hole by crushing it to its Schwarzschild radius, can we do the same process in two different points in the space keeping the quantum states of both the objects ...
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Negative of Quantum Gates and Entangled States

I'm well aware that using this quantum circuit: $\hskip2in$ $\hskip2in$Quantum circuit used in the generation of EPR pairs. It is possible to create entangled state of two qubits (EPR pairs), in ...
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How many parametric down converters are needed to entangle four photons?

In quantum optics, how many parametric down converters are needed to entangle four photons?
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Never ending quantum superposition? [closed]

So I am wondering over the Copenhagen Interpretation how can a decoherence or measurement ever happen. If in the beginning of the universe everything was in a state of coherence being in ...
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83 views

Wigner Function for an Entangled Composite System

How is it possible to compute the Wigner function for a composite system that is prepared in an entangled state? In particular, consider the state $|ψ_{AB}\rangle=\frac{1}{\sqrt{2}}(|0_A\rangle|1_B\...
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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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145 views

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 ...
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what is a collapse of a state vector or wave function?

I read there are two kinds of explanations on the "collapse of a state vector or wave function". 1) for an arbitrary state vector $|x\rangle=\sum\alpha_n|\phi_n\rangle$ after measurement, $|x\rangle\...
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Mechanism of quantum entanglement; proof of quantumness

A system is said to be entangled if its state cannot be expressed as a product of states. (i.e $\psi_{AB}\neq\psi_A \psi_B$) Physically it is a direct result of conservation of energy/momentum, but ...
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quantum superdense coding -How many qubits are needed?

This is an extract from Wikipedia about superdense coding: "In quantum information theory, superdense coding is a quantum communication protocol to transmit two classical bits of information (i.e., ...
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Quantum entanglement, how do we know there was no spin? [duplicate]

Im not a scientist, so go easy on the explanation! As I understand it we can create two entangled particles. The entangled particles have a spin property which is opposing. When we measure one of the ...
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What are some useful resources for simple two-body quantum simulation?

Are there available, commercial or free, numerical packages for simulating quantum dynamics that have built-in tools especially for quantum mechanics? For the purpose of this question, I want to ...
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A question on the no-cloning theorem

When reading papers on the no-cloning theorem, I understand that one is searching for a unitary matrix $U$, such that for any state $\vert \phi_A \rangle$ in a Hilbert state $H_A$, we have that $U\...
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Von Neumann entropy in the algebraic approach

In the algebraic approach to QM a quantum system has associated to it one $\ast$ algebra $\mathfrak{A}$ generated by its observables. A state is a positive, normalized linear functional $\omega : \...
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How Forces are Represented from Quantum Computation or Entanglement Perspective?

In the fields of Quantum Computation and Entanglement there is content on the structure of quantum systems and artificial quantum systems like qubits and quantum cellular automata. I have even seen ...
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Entanglement in double slit experiment

Suppose we send 2 entangled photons through the 2 slit, does measuring the position of one of the photons affect the other particle's wave function or does the other particle still behave as a wave ?
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If quantum cloning was possible would entanglement enable faster than light communication?

Assume quantum mechanics allowed you to clone particles. How could you use quantum entanglement to communicate faster than the speed of light? In the 1980s a scientist proposed using quantum cloning ...
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Cosmic entanglement

Is there a way to measure the entanglement of CMB photons? Could it be possible to measure such a thing and/or entanglement of photons from stars and/or cosmic neutrinos/gravitational waves and/or any ...
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Does the physical distance between qubits influence the speed of quantum computers?

I've heard lots of talk over the past decade about the potential of quantum computing. Most of what I've read about the topic (mostly articles targeted at the layman) focuses on the exponential ...
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What are unital maps?

In quantum information, one defines an unital map as the one that preserves the identity operator $\epsilon (I) = I$. A popular example is the so-called amplitude damping channel. My question is, ...
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How would a quantum radar detect the state/information change of a remote, unobserved particle?

The Department of National Defence is investing into a technology they are coining quantum radar. The premise is that they would create an entangled pair of photons, and shoot one out into the air ...
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What is the difference between no-disturbance principle and non-contextuality?

The no-disturbance (ND) principle states that, for any three observables A, B, and C such that A and B are compatible, and A and C are compatible, the probabilities of outcomes of A do not depend on ...
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What are the range of values of the negativity in quantum mechanics?

The negativity of a quantum state, given by $N(\rho)=\frac{||\rho^{\Gamma_A}||-1}{2}$ where $\rho^{\Gamma_A}$ is the partial transpose with respect to subsystem $A$ of the density matrix of a ...
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Quantum entanglement of photons proximity

When scientists entangle photons or atoms or other objects, is it only their state that gets entangled? What about their proximity in space? If you move one sideways will you see the other one move ...
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Heisenberg's uncertainty principle and measurements

While studying quantum key distribution, I came across this postulate which states that given two entangled particles A and B at Alice and Bob sites respectively, if Alice measures A to be $\uparrow$ ...
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Quantum entanglement and 'perfect' synchronized measurements [closed]

Given two entangled particles A and B barely separated by a very tiny small distance such as the communication delay between both observers Alice and Bob willing to measure the state of A and B ...
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What is the formal definition of a system?

According to quantum mechanics, bosons can occupy the same quantum state in the same system but fermions cannot because the wave function for the interchange of two identical fermions would be ...
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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=...