Entanglement Definition and 882 Threads

I do not have the education to grasp the math of quantum mechanics but I am very interested in it and understand some of the concepts. I often find myself pondering those concepts. One thing I began to wonder about was the possibility of using quantum entanglement to observe distant objects so...

Maybe I've got this wrong, because from what I've been able to glean, how a particle measurement affects another particle which can be on the other side of the Universe in principle is agreed to be 'spooky' and it seems that everyone is happy to simply say, yes this is very mysterious and...

Here's a simple story. I'm running a pizza delivery store and hit upon a gimmick to increase sales, I call it "Schrodiners Slice". You call up and get paired up with the next caller and your orders are randomly shuffled. Maybe you get your order, but maybe you get the next persons order instead...

Hello, first from all, I am completely new and uneducated in physics. But from nothing I have had idea how to make this invention. And I have quite strong need to share it. My mind found out how we can communicate with no delay through out our universe. Seems quite fancy, isn't it? Yes, quantum...

Given a pair of Spin ##1/2## entangled particles created in the ##z^→## direction according to the following equation ##Ψ=1/√2(\uparrow\uparrow+\downarrow\downarrow)##. One entangled particle is sent to Alice and another to Bob. Now if Alice measures her particle in the ##z^→## direction she...

My understanding is that an elementary particle A becomes entangled when it interacts with another particle B, sharing symmetrical properties with particle B, until particle A interacts with another particle C, whereupon particle A becomes entangled with particle C. When an electron gets fired...

Hi, When a quantum entangled photon is measured to determine spin does it's spin stay in that orientation as long as it's measured it or does it immediately go back to a superpositioned state? In other words if you determined the spin of a quantum entangled particle at say 12:00 pm and...

Does non-entangling environmental noise actually exist? The existence of such a thing seems to be fundamentally inconsistent with the properties of quantum entanglement. It seems to me that if non-entangling environmental noise does exist, then standard QM - or QFT for that matter -...

In book Quantum computing explained by David Mahon concurrence, as a measure of entanglement is defined as C(\psi)=|\langle \psi|\tilde{\psi} \rangle | where ##|\psi\rangle=Y \otimes Y|\psi^*\rangle## or with density matrix ##\rho(Y \otimes Y)\rho^{\dagger}(Y \otimes Y)##. Could someone explain...

Entanglement's non-locality ('spooky action at a distance') depends on the instantaneous collapse at all points in space of the entangled particles' common wave function. The Many Worlds model has no wave function collapse. Does it also have no entanglement?

This is a thought experiment I had with myself a couple of weeks ago. I have never seen it proposed. But please be kind I am not physicist but just a hobbyist. So this experiment is specifically for entangled photons. So here goes. I was thinking of something going faster and faster and time...

I was studying about the quantum entanglement phenomena and got introduced to the concept of EPR paradox. From this juncture, I see two schools of thought, one describing quantum mechanics as a probabilistic description and the other brings into question the local hidden variable theory. These...

I want to know what are the QFT topics that I need to understand in order to proceed in reading papers on entanglement entropy such as, Entanglement Entropy and Quantum Field Theory Entanglement entropy in free quantum field theory Entanglement entropy: holography and renormalization group An...

Hi. Over the years I've read LOT of "popular science" (i.e. non-textbook) books on entanglement, and on the explanations / objections / arguments Einsten, Bohr, Bohm and others had that still remain today. There's one aspect which never seems to get covered in these books and I wondered if...

Suppose we produce a polarisation-entangled photon pair ##A_1## and ##A_2##. Then we entangle another pair ##B_1## and ##B_2##. Now suppose that these photons will not interact with anything, sending ##A_1## and ##B_1## to Alice and ##A_2## and ##B_2## to Bob. Alice measures the polarisations...

Hi I hope that you will humour me as I try, in layman’s terms to explain a question I have. I recently watched BBC4’s excellent program about quantum entanglement and it got me thinking. I am aware that there are currently experiments ongoing to prove that quantum entanglement is real and...

1) Entanglement is about the behaviour of a particle can be determined by measurement of the behaviour of another particle. At some website, it explains that the reason behind is due to conservation of momentum. When a particle is split into two particles (say particle A and particle B)...

Afshar's experiment (https://en.wikipedia.org/wiki/Afshar_experiment) sent a light beam through a double-slit to get interference, put wires in the places where there were dark fringes, then refocused the light with a lens get "image" the two slits. I'm wondering what entanglements would break...

Reading about the HOM effect, two photons come to a half-silvered mirror from opposite sides but they both end up going the same way - one always reflects while the other transmits. Which path they take is random but they both take the same path. Is the path they end up on initially a...

Dear community, I frequently have problems imagining the EPR paradoxon, hence how I can imagine entangled states. Let's say we have the Bell state of the basis /0> and /1>: Ψ = 1/√2 (\00>+\11>), where the first element of the ket belong to particle/qubit 1 and the second element to...

Three related questions: (a) In a pair of entangled particles, after one is measured/observed/determined/collapsed, my understanding is that the measurement breaks the entanglement so that after the measurement, unless something happens to re-entangle them, they are no longer entangled. Correct...

What I know of this only comes from popular presentations of the subject. So let's say there are two particles, A and B, known to have opposite values of a particular property such as spin. We don't know which particle has which spin until we measure the spin of one of the particles, say A. Then...

As a Computer Programmer, it's hard to wrap my head around Quantum Entanglement and non locality being explained in the context of Classical Physics. In other words, if the universe at it's core is physical where does Quantum Entanglement fit within a physical picture of reality? There's been...

From what I know about (bi-partite) entanglement, we write the combined Hilbert space as a tensor-product of Hilbert spaces for a particle at ##A## and a particle at ##B##, ie ##\mathcal{H} = \mathcal{H} ^{A} \otimes \mathcal{H} ^{B}##. If the particles share a non-separable state, they are...

Has there been an experiment where 2 particles that are entangled are measured at the same time? If so what was the result? Can any observer occupy the same frame of reference down to an electron? Don't we all exist at different times based on our frame of reference so none of us can share the...

Why two bodies are related with each other despite the distance between them. It is unbelievable that entanglement exist regardless of any distance. Why on universe are so deeply connected with each other where distance does not play any role for the phenomena?

I am building an SF universe. While it is very similar to ours, but casual FTL exists. I don't think Lorentz transformations shouldn't work at all, but rather extra dimensions can somehow circumvent them. One kind of FTL is direct communication through entanglement. There can be two version of...

I should first acknowledge 2 important points. I don't read papers on QFT, and therefore barely know how to spell it. And second, although I read many papers on entanglement (theory and experiment) I don't know if I have ever seen much reference to anything I might label QFT (that being...

1. An elementary particle like a photon or electron can be measured in 2 possible states - spin up or down in electron, vertical or horizontal in photons. We'll call those states state 1 or 2, and the measuring device state A or B. If for example, we measure a photon with a polarizer in State...

If an entanglement experiment, whereby an entangled pair of particles is measured at both ends, is independent of the next entanglement experiment with another pair of entangled particles, how can there be a correlation? It seems that each independent run does not influence the next run, but...

Why can't absolute time be used to describe events? Previously I tried to describe entanglement collapse on this forum in terms of absolute time, but I was told more or less this was not valid. I don't understand why. If the proper time that we use is based on the fact that the speed of light...

As far as I can tell nobody actually knows how quantum entanglement really works, and yet everyone assumes that quantum states are teleported faster than light. But what if there isn't any actual teleportation, because both sides still share the same position? Maybe in a dimension we cannot...

This thread is to look at the notion of wave function collapse and relativity of simultaneity. The other thread I started on QFT has helped to clarify a lot, so hopefully this one can do the same. I may have this all wrong, but I will outline my question and hopefully someone can point out...

First, how is a computer bit attached to a photon? Why does entanglement allow for two bits? How is it nonlocal?

A photo: https://petapixel.com/assets/uploads/2019/07/quantum.jpg The popular press version (with above photo): https://petapixel.com/2019/07/13/this-is-the-first-ever-photo-of-quantum-entanglement/ The full paper in Science Magazine: https://advances.sciencemag.org/content/5/7/eaaw2563

Is Quantum information theory the only theory that handles multi partite entanglement? I have been digging through the net but the only papers I have come across are quantum information theory based. Though I don't have an issue with QIT, I would prefer to study examinations done with...

The problem with this is that only one push's worth of energy was expended. One push's worth of input cannot produce two push's worth of output, for this would violate the law that says you can't get more movement out of something than the amount of force you exert onto it (to put is very...

Let's consider Bohm's paradox (explaining as follows). A zero spin particle converts into two half-spin particles which move in the opposite directions. The parent particle had no angular momentum, so total spin of two particles is 0 implying they are in the singlet state. Suppose we measured Sz...

Suppose I "produce" positron-electron pairs one at a time (by produce I mean in plain language the inverse of annihilation). Next I measure the vector of the magnetic moment of each positron. Is each pair that is produced entangled? Without measuring the electrons, can I now be much more certain...

Which of these premises is impossible or incorrect according to our current understanding of quantum entanglement? Given 2 entangled particles, p1 and p2: Observing paired particle p1 induces a change in spin on paired particle p2. There a way of detecting a change in spin on particle p2...

In a recent study (https://phys.org/news/2018-08-flaw-emergent-gravity.html) it has been discovered an important flaw in Emergent/Entropic Gravity because it has been discovered that holographic screens cannot behave according to thermodynamics... But then, doesn't this also invalidate...

I'm happy to admit that I am struggling to digest this recent arXiv paper - https://arxiv.org/abs/1904.11974 - but I am interested in whether its reasoning and provisional conclusion seems insightful or merely interesting. My summary of their work is that the researchers consider colour...

Is it theoretically possible to target a distant particle and entangle it with a near particle? Or is entanglement only possible with close particles?

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 good entanglement measure are exhibit. One of these properties that one would consider...

I have recently been reading some stuff on quantum information in the physics literature which refers to 'a mechanism by which a measurement in A determines quantum coherences in B', where A and B are subsystems of a larger system. I am aware of the meaning of the terms 'decoherence' and...

I should clarify, I am a linux administrator by trade and I have no physics or scientific background outside of working at a medical institute, So if my ideas are off and seem wild and misguided, please forgive my ignorance, and while you are at it be grateful for a fresh perspective. (joke) So...

Hi everyone, Could anyone recommend a good QM textbook (undergrad-ish level) or some lecture notes that treat entanglement from the ground-up? Most of the stuff I have seen online on entanglement seem to fly pretty quickly into information-theory or abstract group-theory type stuff, which I am...

Hi all, I have learned the very basics of entanglement (discrete, 2 particle systems) and was hoping that someone can recommend introductory (undergrad-level) material for continuous-variable, 2 particle entanglement. Stuff I have found online so far (like this...

Hi. As far as I understand the Franson interferometer, the photons are in an entangled state like $$\left|\Psi\right\rangle=\frac{1}{\sqrt{2}}\left(\left|\text{short}\right\rangle\left|\text{short}\right\rangle+\left|\text{long}\right\rangle\left|\text{long}\right\rangle\right)$$ if the setup...

Hello all, I have read that these two properties are complimentary, similar, at least in a sense, to uncertainty between momentum and position. John Cramer used what he referred to as a Sagnac Source to vary the balance between entanglement and coherence. What, physically, has to be done to...