Quantum entanglement is a physical phenomenon that occurs when a group of particles are generated, interact, or share spatial proximity in a way such that the quantum state of each particle of the group cannot be described independently of the state of the others, including when the particles are separated by a large distance. The topic of quantum entanglement is at the heart of the disparity between classical and quantum physics: entanglement is a primary feature of quantum mechanics lacking in classical mechanics.
Measurements of physical properties such as position, momentum, spin, and polarization performed on entangled particles can, in some cases, be found to be perfectly correlated. For example, if a pair of entangled particles is generated such that their total spin is known to be zero, and one particle is found to have clockwise spin on a first axis, then the spin of the other particle, measured on the same axis, is found to be counterclockwise. However, this behavior gives rise to seemingly paradoxical effects: any measurement of a particle's properties results in an irreversible wave function collapse of that particle and changes the original quantum state. With entangled particles, such measurements affect the entangled system as a whole.
Such phenomena were the subject of a 1935 paper by Albert Einstein, Boris Podolsky, and Nathan Rosen, and several papers by Erwin Schrödinger shortly thereafter, describing what came to be known as the EPR paradox. Einstein and others considered such behavior impossible, as it violated the local realism view of causality (Einstein referring to it as "spooky action at a distance") and argued that the accepted formulation of quantum mechanics must therefore be incomplete.
Later, however, the counterintuitive predictions of quantum mechanics were verified in tests where polarization or spin of entangled particles was measured at separate locations, statistically violating Bell's inequality. In earlier tests, it couldn't be ruled out that the result at one point could have been subtly transmitted to the remote point, affecting the outcome at the second location. However, so-called "loophole-free" Bell tests have been performed where the locations were sufficiently separated that communications at the speed of light would have taken longer—in one case, 10,000 times longer—than the interval between the measurements.According to some interpretations of quantum mechanics, the effect of one measurement occurs instantly. Other interpretations which don't recognize wavefunction collapse dispute that there is any "effect" at all. However, all interpretations agree that entanglement produces correlation between the measurements and that the mutual information between the entangled particles can be exploited, but that any transmission of information at faster-than-light speeds is impossible.Quantum entanglement has been demonstrated experimentally with photons, neutrinos, electrons, molecules as large as buckyballs, and even small diamonds. The utilization of entanglement in communication, computation and quantum radar is a very active area of research and development.
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?
Let be an entangled pair of photons 1 and 2, with the same polarization. The wave function is
##|12>=\cos\psi|HH>+\sin\psi|VV>## with ##\psi## the angle of polarization. The first ##H## (##V##) in ##|HH>##
(##|VV>##) is photon 1, and the second one is photon 2.
Alice observes photon 1 with a...
https://quantum.phys.lsu.edu/old-website/seminars/abstracts/Kaushik10.pdf
I have discovered an experiment in the link above where you get NOON entangled states by mixing classical laser light with quantum light from SPDC. But I cannot understand the mathematics behind it. Can you explain it to...
I'm reading this article about quantum entanglement, and the author writes about a process in a Raman transition which would break the entanglement, and I'm interested about how it breaks the entanglement.
So the passage which I'm interested in begins with: "The answer is to do an operation...
According to professional scientific literature and to our best understanding, are there any suggestions that entanglement might imply some sort of faster than light signaling between the entangled particles?
I know that according to relativity nothing can travel faster than light, but what...
if I have two particles in an entangled state, I make them travel in different directions, and I measure the state of only one of them then I know the outcome of the measurement of the other.
But when I take a measurement on the first particle, what happens to the second? Does it undergo a...
What is entanglement in QM and QFT?
I understood that it only corresponds to the concept of linear combination of states with multiple particles. Seeing lectures on YB it seems to me that it is something much deeper than that. What did I miss? How is it treated in QFT?
I am studying NRQM from...
I was doing some research into quantum entanglement but it is never well described how you break the bonds once they are formed does anyone have any expertise in this area on how to break quantum entanglement bonds? The best that I can understand is the bond is broken when interaction with the...
As my current studies have proven conservation of energy is a universal law. How is it possible for two entangled particles to be equally or similarly affected when a force or energy is applied to a single member of the entangled pair? The production of such a pair would be invaluable to...