Stack Exchange Network

Stack Exchange network consists of 174 Q&A communities including Stack Overflow, the largest, most trusted online community for developers to learn, share their knowledge, and build their careers.

Visit Stack Exchange

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.

-3
votes
3answers
172 views

What's the fuss over quantum entanglement about? Is it because people have misunderstood? [closed]

The first video I've seen about quantum entanglement claimed that changing A's spin will immediately take effect on B's spin as well. The more I read into this topic the less it seems that this is ...
1
vote
1answer
65 views

Is quantum entanglement “observer dependent”?

See also here. According to the answers of the mainstream entanglement should be objective. Once more this question asked in a more mathematical way... Any vector $|{\psi}>$ of norm 1 in a Hilbert ...
0
votes
3answers
139 views

Questions on Bell's theorem and Disproving the hidden variable theory

I'm not a physicist (computer science background), but always was fascinated with the concept of entanglement. As many, the first intuition I had was - well, the two particles share some knowledge ...
5
votes
1answer
286 views

The term “Coherence” is overloaded!

I have troubles with modern terminology in the field of quantum information technologies. There are a lot of new terms that everyone is using and no-one takes time to explain, even though modern ...
1
vote
0answers
52 views

A hollow black hole & quantum entanglement?

Let us consider the following thought experiment. we create an entangled pair of particles and we separate them. next, we would place 1 particle inside a massive hollow sphere and the other particle ...
1
vote
1answer
102 views

Reconcile a pair of two-qubit boundary-state separability probability analyses

It is now clearly well-established--though formalized proofs are still largely lacking—that the probability, with respect to Hilbert-Schmidt measure, that a generic two-qubit state is separable/...
0
votes
0answers
26 views

Peeking inside Schroedinger's Black Box (not his cat box)

While exploring variations on Shroedinger's Cat, I came up with the following puzzle: Define a Schroedinger's Black Box (SBB) as a volume whose contents have no causal connection to an observer A. ...
3
votes
2answers
84 views

Do time crystals require quantum entanglement?

In this video (at this time in the video) the vlogger seems to make a statement that the only way time crystals can be achieved is if some of the atoms (at a periodic distance from each other) are ...
2
votes
1answer
97 views

Are *all* quantum states indeterminate if they are outside the observer's light cone?

Is the state of a particle arriving from outside an observer's light cone merely unknown, or is it quantum mechanically indeterminate? I guess the question needs a background in the form of a ...
-3
votes
4answers
151 views

Is the common interpretation of quantum entanglement just a perversion? [duplicate]

The idea of spooky action at a distance seems to imply that the information was always present at each end, but the common interpretation is that information can be transmitted instantaneously. Is ...
3
votes
1answer
55 views

Are the phases of entangled photons correlated?

I know the polarization of entangled photons are correlated, but are the phases of the wavelengths correlated as well?
1
vote
2answers
89 views

Current quantum theory does not offer a dynamical mechanism to account for energy transfer in position-measurement, WHY?

In Quantum Mechanics (vol. 1) by Tannoudji et al., there are two pages discussing "perturbation created by a position measurement" (p.278-279). They consider a particle in an infinitely deep potential ...
2
votes
1answer
71 views

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 ...
0
votes
0answers
24 views

What exactly are Joint measurements?

So far, I understand what is LOCC. In the literature there is also another kind of measurement usually referred as joint measurements. I wonder if someone can explain the exact meaning of this joint ...
1
vote
0answers
39 views

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 ...
2
votes
1answer
65 views

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 ...
0
votes
0answers
50 views

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 ...
2
votes
3answers
114 views

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 ...
0
votes
1answer
32 views

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?
-1
votes
1answer
115 views

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 "...
-4
votes
1answer
121 views

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 ...
2
votes
1answer
81 views

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?
-1
votes
1answer
85 views

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 ...
0
votes
1answer
28 views

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\...
2
votes
0answers
44 views

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 ...
0
votes
1answer
62 views

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 ...
0
votes
0answers
24 views

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?
-3
votes
1answer
64 views

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 ...
0
votes
1answer
74 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\...
2
votes
1answer
98 views

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 ...
1
vote
1answer
72 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 ...
0
votes
1answer
42 views

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 ...
0
votes
1answer
76 views

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?
1
vote
1answer
48 views

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 ...
1
vote
1answer
68 views

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 ...
6
votes
2answers
104 views

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. ...
0
votes
0answers
16 views

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 ...
1
vote
0answers
31 views

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 ...
3
votes
0answers
251 views

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 ...
0
votes
0answers
31 views

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 ...
2
votes
2answers
75 views

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 ...
0
votes
0answers
35 views

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\...
1
vote
4answers
255 views

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 ...
1
vote
1answer
108 views

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., ...
1
vote
3answers
105 views

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 ...
0
votes
1answer
39 views

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 ...
3
votes
1answer
79 views

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\...
4
votes
0answers
111 views

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 : \...
2
votes
0answers
53 views

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 ...
0
votes
2answers
147 views

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 ?