Entanglement Definition and 870 Threads

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...

hi there I am an engineer but have a huge interest in physics and wanted to ask anyone who has any knowledge of why quantum entanglement occurs?

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...

What is the mechanism behind Quantum Entanglement? Why do only subatomic particles exhibit Quantum Entanglement?

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...

Suppose Alice and Bob do an experiment with an entangled pair of particles, for instance electron spin with SG magnets. Now suppose Alice her SGM is stationary while Bob his SGM is switching fast between parallel to Alice and perpendicular to Alice. So there are two possibilities: correlation...

Hi everyone, background for my question is here: and https://www.researchgate.net/publication/45424433_Direct_generation_of_photon_triplets_using_cascaded_photon-pair_sources: My question is whether it's possible to determine if two photons are entangled without using a coincidence counter...

Hello, I am currently studying about entanglement on spin-1/2 chains and I was able to find some information about the mathematical point of view of concurrence but I can't understand the physical meaning of it . Can somebody help me, please?

hello: I don’t know where to post this and I think this is as good a place as any here. question: does quantum entanglement explain how we are? I am having trouble Even trying to express the question above. But, I just viewed PBS space-time series 6 episode eight: “how do quantum states...

Quantum Entanglement & Spooky Action at a Distance! Bell's theorem.

Suppose particles P1 and P2 are spin entangled in singlet state, then, if someone claims that IF particle P1 is found to be in spin-up state when measured, that THEN particle P2 is in spin-down state, does that follow from the minimal formalism, or is it just an assumption?

I work in IT and am a layman in the quantum world. I have obviously misunderstood something in my amateur reading of quantum, but if someone could explain my mistake in the above scenario it might be very insightful for me! Forgive me if the terminology is not correct - or if indeed lay folks'...

Suppose someone entangled 2 particles many years ago and kept particle E here on Earth and sent particle S a light year away from Earth. So the observation of particle E on Earth would fix the state of particle S a light year away. But they did it in such a way that observing particle E would...

I have a source that says when two particles are entangled, we must describe them using the density operator because it is a mixed state. But I have another source that says that the singlet state of two spins is an entangled state, but that has a wavefunction. So could someone explain what I am...

Very confused about this article and the experiment it's based on. I'm not very knowledgeable on this, but I'm very confused on what's happening here. It seems extremely weird to me

Most of my questions are from these articles: https://www.google.com/amp/s/www.sciencealert.com/if-you-thought-quantum-mechanics-was-weird-wait-til-you-check-out-entangled-time/amp https://www.scientificamerican.com/article/how-einstein-revealed-the-universe-s-strange-nonlocality/...

Could quantum entanglement be used to send faster-than-light communications across vast distances in space, in the distant future? For example, if humans establish permanent colonies on Mars, it would take some time to send communications between Earth and Mars. Could a future technology...

If I understand the idea of EPR correctly, the quantum entanglement occurs between two particles for which the total momentum is known (therefore, knowing the momentum of one particle, one can recalculate the other, and this contradicts the uncertainty principle). Then the question arises...

[This](https://youtu.be/9l6VPpDublg) is a lecture by Persinger where he postulates that photon entanglements and the Earth's magnetic field can facilitate telepathy. (See from 20:00 to 30:00) Links to the study he cited...

If quantum objects’ superpositions decohere rapidly due to exposure to a surrounding environment, why have I heard it said that two entangled particles can be a large distance apart while still having undetermined properties? Wouldn’t decoherence occur while the particles were moving apart?

As a follow up from my other thread, where I consider popular media describe entanglement sort of as: and I think this may be wrong. As a follow up question I want to put forward this: A singlet state of entangled particles is notated in a superposition of product states as: ##|up, down...

They say spin up and spin down is correlated at at any distance and that it can’t be explained by basic logic. say I rip a photo in two, shuffle them and put them in two boxes and send them light years away. No matter which box I open, I can’t know which half I have but when I open it the photo...

In some popularized discussions of entanglement, you often hear that: This seems to me not necessarily the case. In this formulation, particle A is viewed through measurement outcome and particle B through ontology. If the measurement basisses of Alice and Bob are parallel, Alice's outcome...

I am fascinated by entanglement. I have a theory but it's not based in enough physical knowledge for me to say whether or not it makes sense. I suspect on the quantum level that time looses its ability. Thus, distance would lose its significance. So when I hear spin can be affected at any...

First, I was not sure whether this should go into the Relativity or the Quantum Physics rubric, but since the central question is about entanglement, I opted for the Quantum. I do not have the necessary sophistication to follow string theory arguments, and even most explanations in...

Hello, there. I am studying a model for decoherence of two entangled photons. The space for the first photon is 2 dimensional, while that for the other one is 6 dimensional. In total, the system will be in a 12 dimensional space. Initially, they are set to one of the Bell states, such as...

Hello! I would be really thankful if you could recommend me a good book for an introduction to quantum entanglement . Thanks!

Is it possible to downconvert an entangled photon and could that mean three particles get entangled and why not? Thanks! :)

Hey all, I need help with the book I'm currently writing. What would it take (even theoretically) to use quantum entanglement for FTL data transfer? From what I understand, the state of entangled particles can not be changed without breaking the entanglement. Do you think this would ever be...

This is the paper and here is the video. As far as I know, this is an entanglement related experiment done so far in such a large scale. I want to know whether entanglement related experiment has been done so far on a larger scale and what can be the possible use of such phenomenons.

Hey all, there is something I'm having trouble with here. If two entangled particles are created and then separated, say one is on Earth and the other in near-earth orbit (like the Chinese experiment), and the one on Earth is measured at say a vertical spin of -1, and at the same time the one...

I started another thread on this but it went off into other topics. Hoping to focus on the math here, specifically whether or not the model presented in here is consistent with QM. Let's measure the polarization at the same angle ##\alpha = \beta = \pi/3## (##\varphi_1=0...

I'm an undergrad in physics, and have been asking myself the following question recently. Suppose you have a pure quantum state p (von neumann entropy=0), made of 2 sub-states p1 and p2 that are entangled. Because they are entangled, p \neq p1 x p2. Hence the entanglement entropy of p (=0) is...

If I were viewing the Earth from high above the North pole, I would notice it spinning in an anti clockwise direction BUT when viewed from the South pole it would be spinning in a clockwise direction. If I were high above the equator oriented in a "North up" position I would observe the globe...

Dear PF Forum, I've been having this question for a long time. I want to know how or what is measurement. Supposed there are two observers. Alice and Bob, They are separated 10 light minutes away. They are in the same frame of reference, meaning that their distance is the same all the time...

As I understand it, either coherence or entanglement can be in an experiment or some of each, varying continuously between the two. Because of this, coincidence detection is needed to pick out interference patterns among all the data. Coherence would refer to quantum waves of photons taking...

I am asking a very basic question. Asking for clarification on the procedure for preparing quantum particles in an entangled state. My question asks if once the particles are prepared along a certain axis, is it then true that the intervention is then removed so that each particle can become...

Hello, I have a question about the creation of the Bell's entanglement state ##1/\sqrt{2} (|HH> + |VV>)##using type I BBO crystals (https://en.wikipedia.org/wiki/Spontaneous_parametric_down-conversion). Two crystals are put orthogonal to each other and each of them emits a photon pair...

I am just starting to learn quantum mechanics. And have some questions on entanglement. I have learned that when there is two particles entangled that they share the same wave function and cannot be considered by themselves. I am having a hard time understanding some of the nuances of this...

There is something I don't understand called CV Bell state measurement. In these two experiments they get two entangled beams "by overlapping phase-squeezed light with amplitude squeezed light with a phase difference of pi/2 at a 50-50 beamsplitter" See Figure 11...

Consider page 2 of Toth's paper Entanglement detection in the stabilizer formalism (2005) . To detect entanglement close to GHZ states, they construct entanglement witnesses of the form $$\mathcal{W} := c_0 I - \tilde{S}_{k}^{(GHZ_N)} - \tilde{S}_{l}^{(GHZ_N)},$$ where...

For a thought experiment, if you defined: An electron's "state" can be in 16 states measured as increments of 45 "degrees" starting at 22.5 (modulus 360) An entangled electron (e') simply gets aligned 180 degrees away from (e) A "measurement" M(n) at n degrees simply adds n degrees "Spin" is...

Suppose photons 1 and 2 have entangled spins. And, so do 3 and 4. A Bell-state measurement (BSM) is performed on photons 2 and 3 to cause entanglement swapping so 1 and 4 are now entangled. This is done many times creating many 1 and 4 pairs. Suppose the original 1s and 2s were prepared such...

There we read: "note that if Wigner did not know this phase due to the lack of control of it, he would describe the “spin + friend’s laboratory” in an incoherent mixture of the two possibilities". Why is this the case? Given that the author has propoede neither a citation nor a proof for this...

Maybe my question is naive and due to my not deep enough knowledge of particle physics. I imagine we entangle two particles on Earth and then send one on spaceship going from Earth - two coordinate frames moving in relation to one another. Moments of simultaneity are different for them. When...