Entangled Definition and 270 Threads

Let's suppose that we have an entangled state of two systems ##A## and ##B##: $$ \frac{1}{2}\left(|\psi_1 \phi_1\rangle+|\psi_2 \phi_2\rangle \right) $$ where ##|\psi \rangle## and ##|\phi \rangle## are energy eigenstates of ##A## and ##B## respectively. However the eigenstates##|\phi_1\rangle##...

The first spin analyser is orientated on the z-axis and the second is in a arbitrary N-direction. My thought process I can't get past is below If I find particle 1 to have spin up in Z-direction, the state collapses and the second must be spin down in the Z-direction for the particle at the...

I understand that we can create entangled particles in the lab. But how many (non-locally) entangled particles (such as photons/polarisation or electrons/spin) exist in free nature?

The reason I ask is because by definition entangled particles, like electrons, are always precisely the opposite spin of each other. At the same time it's known that for electrons to share an electronic shell with another electron, that they too must be precisely the opposite spin of each other...

Perhaps someone can show me some simple math showing two states in superposition and entanglement so I can see how entanglement relates to superposition. Thanks.

Entangled particles give no interference. What happens in the Fraunhofer approximation when the source of entangled pairs is far away? If it depends on distance what about the apparent collapse?

Is it possible to produce an entangled photon pair and be able to delay the reception times by introducing something like a fiber bragg grating which has multiple indices of refraction which propagate wavelengths at different frequencies? Or will, because of their entangled state, do some...

I'm sure this idea has been considered since the invention of the particle accelerator. What would happen to an entangled particle if it's pair was collided in an accelerator? My guess is simply an end to entanglement but I'm too curious not to ask.

Consider two polarisation-entangled photons A and B fired at two polarisationfilters that are at a certain angle α. Are the probability that A is passing its filter and the probability that B is passing its filter indepedent probabilities? I am aware that is probably an incredibly stupid...

By heating calcium in a tantalum oven and subjecting the calcium vapor stream to blue laser, calcium atoms absorb the blue photons and emit two photons of lower energy as they decay twice. Once they decay from the highest excited state to an intermediate excited state, and then from the...

I think this is just a quickie. I'm interested in what is assumed about entangled photons/particles before they are observed. Is it correct to assume that the photons/particles exist in all possible states simultaneously? Thank you.

If a photon A is entangled with photon B and one somehow destroys photon A, what will happen to photon B? Will it also get destroyed? And can two entangled photons combine into one?

Each particle has a wave associated to it according to the principle of wave-particle duality. Between two waves there is a phase difference. What is this phase difference in the case of entangled particles? 0 degrees? 90 degrees? 180 degrees? Somewhere in between?

On Wikipedia, an article appear from which I quoted below. Here is something called Bose-Einstein correlation due to interference of wave character that I confuse with quantum entanglement. I want to know if these BEC correlations are entangled or separable states...

I just read this paper and it was very interesting. The paper is called "Experimental Test of Quantum Histories" http://arxiv.org/abs/1601.02943 Here's some of an article about the paper. https://www.sciencenews.org/article/quantum-histories-get-all-tangled I have been reading a lot lateley...

I was reading an interview of Dr Subir Sachdev in the latest online issue of Quanta Magazine, and he mentions that Cooper pair electrons in the high temp superconductors (HTSC's) are globally entangled with one another, but in the low temperature (type 1) superconductors, they are not, and I...

I've gotten interested in this question since the recent loophole free bell test performed at Delft University (group of Ronald Hanson). In this test they use entanglement swapping which I hadn't heard about before. After some research I even found out that there is such a thing as delayed...

I was thinking about entanglement today and found myself struggling to envision entanglement and relativity working together. If I send entangled electrons out in opposite directions, their states are not determined until one of them is observed. I know that. What if one of them passes...

When the spin of an entanglement particle is established, it is said that the corresponding spin of its entangled twin is revealed immediately, (via wave collapse?), and that this interaction can occur across a substantial distance. It has also been said that this immediate interaction can occur...

Suppose we have a creation point C where two entangled photons A en B are produced. 1m in the direction of A is a vertically polarized filter V. 2m in the direction of B is a horizontal polarized filter H. Now, I understand that when photon A strikes filter V, it either gets blocked or gets...

Two particles cannot be entangled in respect to position and momentum, I've read. But can particles be entangled by all other properties, including either position or momentum? For example by energy, momentum, spin and polarization (+some other(s)?) between two photons. I've read in some other...

I don't have clear how two particles initially "independent" in the sense of "not entangled" become then entangled because of their mutual interaction (and in this last case, when and how I can say they "interact"?). How do I know how should they approach or how strong their interaction should...

Hello^^ It's always interesting to ponder the various ways that quantum entanglement *appears* to allow transmission of faster-than-light information, but on closer examination, actually doesn't. One that occurred to me today was the situation of two persons who receive each of a pair of...

I am curious if photons are quantized because their 'parent' particles are quantized, and the photons are entangled with their parents. In other words, if you were to have two entangled particles emit a photon(s) that is entangled in energy somehow, do they emit a single photon, two photons...

I create 1000 pairs of entangled particles and let them travel very far away. Then I let the 1000 right particles pass through a double slit experiment. At the time when the right particle has passed the slit, but not yet hit the screen, I can choose to detect the 1000 left particles. If I...

Suppose that we can create a pair of wave-packets at 2 places in opposite directions to each other. For example, from the origin at x=0, many waves of different frequencies are emitted in 2 opposite directions to form 2 wave-packets at x and -x where the maximum superposition occurs. Will those...

I was trying to understand the QM tests done to show the violation of Bell’s inequality. In the example given this was done by testing the polarization of entangled photons which were positively correlated. So in the example Alice and Bob are detecting the polarisation for the two entangled...

I am not clear on the below, so any additional information would also be good. Let's say a pair of photons is entangled on 2 properties. When we measure on property A -- the values for property A (for both the entangled photons) becomes determinate/locked/fixed when we measure on property B...

How is the wavefunction of one particle with mass, m, and velocity v affected by a nearby particle that has it's own wavefunction with mass, M and velocity V. Can the interaction of these wavefunctions be through any other means than entanglement? Can the wavefunction of a single non-entangled...

Hi All, I'm in the beginning stages of writing a quantum computer emulator, primarily to get all the concepts down. I've got an excellent Bloch sphere with a Bloch vector that I can duplicate as many times as I like. However, I'm now tackling entangled states. I'm struggling with identifying...

I would like to create entangled photons at radiowave frequencies. To do this I thought it might help to understand as much details as possible how entangled photons are created by parametric down-conversion. Since the down-conversion doesn't happen often, what are the special conditions? Are...

I apologise in advance for my rather minimal knowledge of physics. Please assume that anything I write below is just my current understanding, and may very well be incorrect... Elementary particles decay into other elementary particles. When a a subatomic particle decays into a pair of other...

If one was to entangle two particles and either send the two particles at each other, or send one of the entangled particles and observe the other; what do you think might happen? If there are any problems with getting an entangled particle into the Hadron Collider, please say so.

Greetings, I am interested in conducting a retro-causality experiment to send a bit of data back in time. I would like to delay how long it takes one of a pair of entangled photons to reach a part of the experiment for an extended period of time such as an hour. What ways are there to keep...

What exactly entangled-spin pairs do in Stern–Gerlach experiment that ordinary particles pairs with opposite magnetic dipole moments do not? http://upload.wikimedia.org/wikipedia/en/thumb/e/e2/Bell.svg/600px-Bell.svg.png What equation represents the blue line and what equation if for the...

my question is about the no-communication theorem in quantum mechanics: Assume that i have a pair of entangled photons which are entangled on their polarization. also assume that i send one to alice and another to bob. and alice wants to send a message to bob. no communication theorem states...

Hello everyone, I have a question about the process of spontaneous parametric down conversion (or SPDC). This process is used to create two entangled photons in the visible regime by shining a laser through a beta-barium borate (BBO) nonlinear crystal. My question is, can this process be...

Why is it so important to the universe that if you measure the spin of an entangled pair and its up then the other particle must be down. It seems to have no practical use so why does the universe enforce this rule, how would reality differ if it wasn't true. And is it a law of symmetry...

What is the coherence time for a pair of entangled photons produced in a nonlinear crystal? Is it related to coherence time of the pump photon? Also, if we say that the coherence time of the two photons is T, then does it mean that the two photons can interfere with each other even if their...

First off I'd like to say my understanding of physics isn't very good, so I'm sorry if this question is a non sequitur. Suppose we have two entangled particles, one on Earth, and the other on a ship that is traveling away from Earth at near to light speed. According to quantum...

I am trying to understand something about the problem of self-measurement in entangled system, I will try to do an example, please help me: If we have an isolated system with two entangled, conscious, microcomputers, one, δ with 1 hour cell, and the other β with a 10 hours cell. Here I am...

Does the quantum no-communication theorem apply to multiple particle entanglement as well? To illustrate the idea, suppose we had particles A, B and C with entangled spin. We measure A and B locally using, say, detector angle 0 for particle A and angle 45 for particle B. Particle C is measured...

Hi, imagine setup with source of entangled photons (A and B). Photon A travels to double slit so that either wave or particle pattern can be observed, photon B hits detector either before (setup 1) or after (setup 2) photon A has hit screen. Question: Will setup 1 show interference pattern...

I have been looking up the practical details of certain quantum eraser type experiments and got stuck on a couple of points. I refer to a particular experiment which can be found by googling: "A DOUBLE SLIT QUANTUM ERASER EXPERIMENT" (Sorry I don't know how to include the address) In...

Hello fellow science enthusiasts. The other day I was thinking of a device for instantaneous transfer of data. You would have two entangled particles (or any even number but two just for simplicity), then you would "put" each one in two devices. An input is needed. For example a simple message...

The way I understand it is when particles are entangled, when you measure one the entangled pair is instantly in a measured state. This question really goes to Copenhagen vs. MWI. If Eigenstates of the wave function are entangled, that seems to support MWI. If these Eigenstate are not...

Dear Learned Physicists, can anyone educate me on: is it possible to distinguish entangled particles before and after interaction in theory? what I'm trying to find out is, if two entangled particles can be separated and one interacted with to produce a result at the other end, such...

Hi folks -- quick question. I appreciate that entangled states in quantum mechanics may not be bound states. But when we have bound states, are the particles always entangled with one another? Thanks a lot!

This is how I understand it: Bohr argued that universe was inherently unpredictable as was the spin of the particle, and it was only based on probabilities. Einstein argued that the spin of the particle was actually always the same, just that our physics is not capable of determining it. But...

Hi, If we pump a beta barium borate (BBO) crystal, we get one circle of vertically polarized photons ##\left|V\right\rangle## and an intersecting circle of horizontally polarized ones ##\left|H\right\rangle##: http://quantum.ustc.edu.cn/old/img/image002.gif At the intersection points of the...