Entanglement Definition and 870 Threads

Hi, I was following some discussions here about delayed-choice entanglement swapping (DCES) and its implications regarding causality. I'm recently came across the following paper where the authors provides a forward-in-time analysis that seems to avoid any backwards influence due to the BSM and...

While electron is propagating as quantum wave, we don’t know its, position only possible distribution, so we are (and our detector) definitely are not correlated with its position. When that electron arrives at the position detector, it becomes entangled with it (detector registering position...

I'd like to discuss 3 different examples of photon polarization correlations where we have 2 different, independent sources S1 and S2, each sufficiently distant to each other that the sources themselves are not directly responsible for the correlations. (Refer to this for an experimental...

On pages 94-96 of Helgoland, Rovelli explains Bell violations according to relational QM. He speaks of spacelike separated measurements, one in Beijing and the other in Vienna. He says any talk of correlations between the 2 is meaningless, specifically: "it makes no sense to ask whether the...

There is one question that I would like to get an answer to in regards to the discussion between @DrChinese and @iste in the thread: https://www.physicsforums.com/threads/a-new-realistic-stochastic-interpretation-of-quantum-mechanics.1060576/post-7138288 In the case where the Bell state test...

Hello, I found this paper by Tim Palmer really interesting, about trying to develop a determinist, hidden variables model that doesn't need 'conspiracy' to explain away experimental results around entanglement...

Hello, I'd appreciate some help with understanding how the MWI deals wtih nonlocality. My understanding is most versions of MWI do not include non-locality. To start off this is my understanding of a potential entanglement expeirment: Two particles A and B are entangled then the particles...

I had written a simulator for a quantum computer and wanted to be able to calculate the values of the "purity of reduced states". "Purity of reduced states" is a quantity that IBM provides on their simulator for each qubit. They used to call it "entanglement", and I believe that the two terms...

Say you had 3 particles all of which were entangled in the GHZ format. What methods could you use to measure the entanglement between two of the particles? Say particle A was far away and particles B and C were close together. If you used magnetic fields at point A to break the entanglement...

I was reading a review on single-particle entanglement https://onlinelibrary.wiley.com/doi/10.1002/qute.202000014 and the author says this It's probably a simple/well known result, but I'm not seeing any trivial proof at the moment. Moreover, I'm interested in the general case of arbitrary...

In the following paper, there is a statement which says: Can this procedure be done in the case of thermal AdS, where the boundary is at infinity? [1]: https://arxiv.org/abs/2404.01393

So basically assume both the star and earth have high-tech machines and a mapping of natural changes in orbit such that the detectors will always be the same settings on star and earth, and the ship in between earth and star will move in such a way that the alignment will be exactly halfway in...

Hello! In my summer lab, me and my labmates are trying to generate entangled photon pairs using a spontaneous parametric down-conversion (SPDC) entanglement source with BBO crystals. We're using a 405 nm diode laser from Matchbox with model number 405L-21A. Our setup is as follows: we shine the...

Hi Pfs, I read that pairs of entangled particles were measured on earth along a same direction and that the distance between them was greater than 1000 kilometers. What is the définition of a "same direction" on earth? is Is it related to the direction of a very distant galaxy or somethig like...

Hi, I thought of a mechanism that should allow the transfer of information between two sites (between two places) at a speed faster than the speed of light, at least theoretically. I want to hear what the experts here think about it, because it's quite clear to me that I probably have some...

If we have a pair of super-asymmetrical entwined particles, and move them a light year away so that they retain their quantum entanglement, and we set a clockwise spin as 0 and a counter-clockwise spin as 1. Would it be possible to transmit binary data faster than the speed of light? If we hold...

Could someone please clarify a question that I had? Is it true that 3 or more electrons/particles can be described under one wavefunction, making them entangled? If so, could you use Bell's principles of the comparison of their states like their spin, polarization or position to see if two out...

How do quantum superposition, indeterminacy, tunnelling, and entanglement affect macroscopic phenomena such as tossing a coin, throwing dice, human thoughts, human emotions, decision-making by humans, the behaviour of other sentient animals, photosynthesis, genetic mutation, the speed of light...

IIUC, entanglement sometimes plays a role in conserving come quantity like momentum or spin: the quantities measured for two particles must be correlated in order to get a certain total value. But is this always the case? For example, what, if anything, is conserved in the Hong-Ou-Mandel...

Hi, I am doing my thesis on quantum entanglement and I don't seem to wrap my head around what really happens to an entangled system during a local measurement. I happen to know that information can't travel faster than light I could believe that the collapse of the wave function wouldn't allow...

NOTE: This isn't actually Quantum Foundations or Interpretations, but I thought the audience might be best here. Or perhaps regular Quantum Physics or Astronomy? Not sure. Please move if appropriate. A fun entanglement experiment! How about entangling light emitted from the sun with...

Hello, I'm interested in how measurement, entanglement, bell test etc are handled in QFT. It seems most QFT texts are being quite light on details on the subject. There would be is a preparation step as the start followed by some interaction and a measurement at the end. Interaction is usually...

and how is it known that the two photons are entangled in the first place? I mean before measuring how do you know that you have the correct two photons?

I cannot find a clear answer on the following beginner’s question on some QM fundamentals: Suppose we have two particles, A and B. Let’s say we generated these as (or otherwise entangled them as) an entangled pair with opposite/orthogonal states. Perhaps horizontally and vertically polarized...

Starting from this link my understanding of Bell inequality proof goes as follows: Suppose we have a model of local pre-determinate hidden variables for QM. This amounts to say QM objects are in pre-determinate given states even if we do not measure it. Locality just means that spacelike...

Hi. The classical (Shannon) conditional entropy is never negative. It can be written as ##H(Y|X)=H(X,Y)-H(X)## which allows for a quantum generalization using von Neumann entropy. In the case of entangled states, it can become negative. I guess it should be possible to construct an entangled...

Unfortunately one of the threads about entanglement and Bell tests has again been closed prematurely. It has not been clarified what "locality" means. In the physics community, not involved in philosophical arguments about foundations of QT, it's clearly defined as the property of a...

Hi. As far as I know, entanglement can initially only be created locally, for example by creating two photons at one place in a crystal, or by local forces. Sure, there's entanglement swapping, but the initial entanglement was still created locally. But I only know examples. Is there a general...

Sabine Hossenfelder implies spooky action at a distance is wrong. She says “They seem to think if you do something to one particle in an entangled pair, then that will immediately affect the other one. But this isn’t so. It’s only when you measure one particle, then you have to update the...

In this video how are the entangled photons later used and actually identified as an entangled pair amongst billions of others. Also does he really mean the photon is split or is the quantised energy split with half frequencies?

I have read, what I believe, misleading articles about generating entangled electron pairs. Some suggesting the electron is split. But this isn't possible because it's an elementary particle with charge/mass and Spin properties. So how do we achieve generating entangled electrons with opposite...

So the whole idea with quantum entangled computing, is that particles in superposition can compute more than one thing at the same time, right? But how does a system know which computed result is which? Maybe like a hashtag that separates one from another? But wouldn't that get jumbled, and...

I keep coming across this descriptor, "two (or three) independent, non-interacting parts," in many books on QM (for example, Penrose's Shadows of the Mind). It is usually followed by a mathematical description (for example, state vector |A>|B>). I can wrap my mind around the quantum paradox of...

Hey! I'm new to the forums so its nice to be here. I don't have a deep deep background in physics (I plan to self study after I finish my math studies). However, I recently learned about the notion of quantum entanglement. My basic understanding of it is that quantum entanglement (will use QE...

Suppose two electrons are entangled with opposite spins. Electron #1 passes through the event horizon of a black hole, together with Laboratory Assistant #1. Suppose the assistant measures electron #1's spin after they pass through the event horizon (according to #1's [proper] time) and measures...

Hi, Thanks for having me as a member. I've had a lifelong interest in science, all types of science but particularly in physics. It's the basis of everything isn't it? Biology is based on chemistry, chemistry is based on physics, physics is based on quantum physics and that is based...

I'm conflicted about how hybridization and quantum entanglement can simultaneously co-exist. I'm first confused about how quantum entanglement was proven. I tried to read to proves (I'm in grade 11 and planning on writing an ee on this) and it flew relatively over my head. Hybridization states...

I know very little about quantum physics. I was looking up the definition of quantum entanglement and asked ChatGPT to explain it. Here is an interesting phrase in its answer: "Once the particles are entangled, measurements made on one of the particles will instantaneously affect the state of...

Hi, I have a basic understanding of quantum physics. I was reading a Wikipedia article on hidden variables, https://en.wikipedia.org/wiki/Hidden-variable_theory . The article says the following. I was confused about the words "local" and "nonlocal" in the quote above so I checked out another...

Can entanglement be detected in a single Bell pair? The canonical answer is NO, you can only see the entanglement in an ensemble of Bell pairs. For example, you could look at a stream of photon pairs coming from a PDC source. If you apply the CHSH formula (usually presented as an "S" value)...

quantum connection vs. quantum entanglement Do they mean the same? Are there any differences? Is the second one more common/newer/more standard than the first one? Could someone please answer these questions or recommend something to read?

For this discussion I would like to continue referring to the entangled pairs 1,2 and 3,4 as we have in previous discussions. For background on this discussion refer to post-selection: pre-existing correlations or action at a distance where @DrChinese describes the entanglement swapping...

Suppose the EPR* concept were true as it would be applied to entangled photon polarization. (Please note: I am not saying it is.) They thought QM was incomplete, because there must exist "elements of reality" (hidden variables) that supplied the highly correlated results on entangled particle...

Ok so just tell me this, if you flip a coin with your eyes closed and it lands on your hand and then you look at the coin and it is heads… there was a time in the duration of the coin being in the air at which the coin was in a state of neither heads or tales. But only once it hits your hand it...

Happy new year for all the forumers, My question is about a modification of entanglement swapping: We use to have two sources of maximally entangled pairs (a and A) and (b and B) when a is up then A is also up, same thing for b and B and up and down refer to a measurement along a given direction...

https://www.wired.com/story/this-random-video-game-powers-quantum-entanglement-experiments/ I don't understand the principle of this experiment. The gamers produced random numbers, and what was done with these numbers then? Was the value like <S> in CHSH inequalities computed, and was it...

Hello everyone, I am now doing experiment related to quantum erasure. After plotting the correlation measurement with and without blocking one of the polarization from the SPDC source (say, V polarization), I do not know how to work further on the gating time from the rate of the random...

A follow-up question from a previous thread: https://www.physicsforums.com/threads/is-entanglement-swapping-a-result-of-post-selection-or-a-result-of-a-quantum-operation-called-a-bsm.1047772/. So my point of view is this: there are systems 1-4 (which refer to photons 1-4 in...

I am starting this thread to focus on a point discussed in a QP thread. The relevant experiment is referenced below, which is a very complex experiment intending to remove some of the "loopholes" in Bell tests. For this thread, those loopholes don't matter and we won't reference that element...

What i mean if we change state/spin at one end it will immediately effect the other. Can we see that live using two camera which may be 10 meter apart so that minium time delay. Is there any video proof exist such kind?