What is Entanglement: Definition and 868 Discussions
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.
Look I know I`m a long way from comprehending "entanglement" but could someone help me a bit here. How can we logically say a body is in all possible states until we observe it. Don`t we have to observe it to come to that conclusion? And why can`t Schrodinger`s cat be long dead before we open up...
It is possible to entangle more than 2 photons. A common configuration is to entangle 4 photons, with a common situation as per the following:
Experimental observation of four-photon entanglement from down-conversion
in which the state is described as (figure 1 of the reference)...
As I understand it FTL communication via quantum entanglement would be impossible since it violates causality, but would it be possible to transfer information using QE slower that the speed of light? I recall reading something like that the receiver would not be able to tell whether the...
A friend asked me this question and I don't have an answer for him:
So, we have two particles originating from a common source and traveling entangled in opposite directions and obeying conservation of momentum. After some time the two particles are a fair distance apart. We then make a...
I've been discussing about entanglement and interference on this forum for a while -- whether a single entangled beam can interfere, and why coincidence counting produces interference. I think I finally figured out intuitively how all this works. I know that some people are probably sick of...
I just had one of those lightbulb thoughts a few minutes ago reading someones post. Does observing some particle in an superposed state entangle you with that particle? It makes perfect sense to me right now..
Its definitely like entanglement, even if it isnt. Observing the first observers...
I have a question that seems simpe: if you have two entangled photons, can you set up two pairs of slits (one pair for the signal photons, and one for the idlers) so that observing which slit the idler goes through tells you which slit the signal photon goes through?
It seems that...
If 2 electrons were created at the same time and entangled. And you sent A to the other side of the universe and then you somehow split B. Since the electron being split is connected to the A electron and mimics the electron being split... Would that create matter and would the A electron split...
My understanding is that when you measure an electron's spin on on Axis A, and then on Axis B, the spin on Axis A is "forgotten" and can be something different next time you measure it. Is this correct?
If it is, then how does this work across entanglement? If you measure electron A's spin...
Hello,
I am interested in the conditions necessary for entangled states to be created. Unfortunately I only have access to introductory QM texts, and they talk about about how entanglement can exists between particles etc, but no mention of the creation of them (and the conditions required...
I downloaded William Donnelly's talk, given at Loops'07
Entanglement Entropy in Loop Quantum Gravity
http://www.matmor.unam.mx/eventos/loops07/talks/7B/Donnelly.pdf
maybe he will discuss it with us
I just had a look
Ill start this question with an example of entanglement (to make sure I have it right).
Take two electrons in the ground state of an atom. They are both in the superposition state that is 50% spin up and 50% spin down. You then split these electrons apart, without measuring their state. Now...
People talk about entanglement with such passion and they tell me how big paradox it is, and yet I don't see why. I think maybe I just don't understand quantum mechanics enough? I don't know...
Basically you fire two electrons different directions, and then you can measure 50% chance spin up...
That is, entangling two particles and sending one off in a controlled manner (i'm not sure if we're sophisticated enough to even contain a particle in a quantum state without interference so please fill me in) to a black hole and then observing the entangled particle that we kept in some lab on...
Assume there are two particles which share the same quantum states (that is, if I understand correctly, both are probabilistically identical), but have not been through the process of entanglement. Let's assume they never interacted in any dimensions, they just happened to be identical. Would...
Is the Entropy of the Universe Zero?:(Entropy as Entanglement)
When I began to fully understand entanglement of quantum systems and what this implies, I was in particular excited by the fact that:
a composite quantum system say the composite of two factor systems A and B, can have less entropy...
A friend of mine wrote a paper on entanglement, measurement, and simultaneity.
the professor provided an interesting question, which he felt demonstrated a violation of special relativity. Of course, this is most likely due to a lack of understanding on the professor's part, but neither I nor...
Hello, I have two questions I wish to ask concerning Decoherence and entanglement:
1. I am certainly no expert on quantum mechanics, and while I was reading I stumbled upon the concept of decoherence. I understand the idea, but I have a few questions concerning it:
1. theoretically, if the...
Does anyone know of a reference that describes the effect of adding a quarter wave plate or even a half wave plate placed at 00 / 90 0 and 450 positions in just one leg of a EPR entanglement polarization experiment. This would be in addition to the half wave plate in each leg already in place...
I will make this very clear: http://www.physicstoday.org/vol-59/iss-12/p51.html"
In fact, I strongly recommend you print this out, and give it to people who are not aware of physics, what it does, how it works, and how it permeates through their lives.
This article emphasized so many of...
Flaw in Anton Zeilinger article (Rev. Mod. Phys., Vol. 71, No. 2, Centenary 1999)
This Thread is a continuation from the “Cramer new experiment” thread (see DrC post origin) to separate out comments on an Anton Zeilinger article from the discussion on Cramer ‘Transactional Interpretation’ &...
Ok, I have a handful of questions:
1. Particles A and B are entangled, measuring A colapses the wave function of B, right?
2. The double-slit experiment produces different outcome based on whether or not a particle has been measured, right?
If you have two particles 'a' and 'b' which are entangled with each other and you observe the state of 'a' so consequently you know the state of 'b', if you destroy 'a' will the state of 'b' become unknown again?
Cheers
Jake
Suppose one prepares two particles in an entangled state (at point S) and that one has detectors (say A and B) at opposite equidistant positions, separated by a large distance from S. Now, if one makes a measurement of the spin at A, the spin at B should SIMULTANEOUSLY change to the opposite...
I'm seeing a lot of articles about refining the entanglement process, and how it should be applicable to information transfer, but I haven't seen any experiments where they have actually manipulated the states on one side to be observed on the other. I'm having trouble understanding exactly how...
I've seen little reference material on my question, except the occasional statement that "that is not the case", but no explanation as to why it is not the case.
I suppose this is a common question asked by the layman, but that's me so, I'm asking.
If entangled particles are able to...
LnGrrR
Since the old thread is well off topic from the OP
I’ll continue comments on Entanglement in a new thread And try to “Dumb it down" here
I assume your have trouble following the details on probabilities and why calculating probabilities for an event of grater than 100% or less...
Assume one photon of a momentum entangled pair of photons is absorbed by an isolated atom. Is there now an entanglement between the other photon and this atom? If so, in what way is the atom entangled with the photon?
If the atom after a while emits a photon, under what conditions would the...
just checking:
when one particle of an entangled pair enters a magnetic field, the entanglement is gone as it starts to re-align in the magnetic field's direction, right?
These are probably old ideas (or, perhaps, just stupid), but recently thinking about non-locality it seemed to me that
(a) non-locality clearly shows that time's arrow IS invariant. Physics texts often point out that if you were to make some kind of movie of a physical event such as the...
Talk about not knowing enough on the topic! But it fascinates me to no end...
I've read that, according to Lee Smolin, there are discrete units of space and that there is mathematical support that upon dividing this space, it creates another unit of space of equal "volume".
Furthermore...
I know that if you have two entangled particles and measure ones spin, the other one must have the opposite spin, but what if you have 3 particles entangled with each other, what would happen?
Can quantumly entangled particles be used to send information? I've read that if they could, the information couldn't be sent at greater than c. However, the ability, if possible, to send information via this mechanism would allow information to be sent to another place even if the place is on...
Has anyone read something related? Thanks to point me to such papers, and to express your ideas or knowledge.
The Mach principle aknowledges that a "frame of inertia" can only be conceived with respect to the whole bulk of nearby universe. That is to say that physics frame of reference is...
I am confused by the descriptions of entanglement I have read. Some seem to imply there is a superluminal transfer of information going on, while other descriptions do not. Can anyone explain this simply? I have a B.A. in Math, but am self taught in physics.
Might quantum entanglement explain the cosmological constant, isotropy, flatness, magnetic monopole and horizon problems? Instead of inflation introducing a phase change that caused an exponential expansion in the early universe, perhaps entanglement has maintained a statistical causality...
I read about quantum entanglement in an article about teleportation I read on the web.
If two particles can be connected despite an enormous distance, in such a way that the properties of one can be transferred to another, even though no wire or string is linking them, can you use this...
Entanglement and information seem to be the new buzz words in the particle
camp, two theories that seem natural to me, but should include QG to make
a workable quantum universe.
If particles carry information by spin ,and exchange information by entanglement
how would gravity communicate?
http://arxiv.org/PS_cache/quant-ph/pdf/0506/0506113.pdf
Title: Entanglement in an expanding spacetime
Authors: J. L. Ball (Oxford U.), I. Fuentes-Schuller (Oxford U. and Perimeter Inst.), F. P. Schuller (Perimeter Inst.)
Comments: I. F-S published previously under Fuentes-Guridi
We show...
I read up on wikipedia.com about entanglement and teleportation but it left me with a few questions. If you go to This Link. You'll see that they give the analogy "Bob has created two atoms called I and II which are maximally entangled". Now obviously, bob can't create two atoms at will so how...
Soppuse Alice have two particles A and C that are in a partly entangled state
|Y(A,C)>. We also have another person Bob (ofcourse) with whom Alice share a pair of entangled particles D and E in the singlet state.
Now suppose Alice make a measurement on her two particles C and D, she...
I need a bit of clarity on quantum entanglement... Any of the 'Bell experiments' will do, but for the sake of discussion, I'll reference http://roxanne.roxanne.org/epr/experiment.html .
Now, the data is obviously in favor of the predictions of QM. Admittedly, I am currently unable to...
Hi all,
1) does the Compton-scattering produce an entangled state?
That is, if I measure the energy of the photon, the energy of the
electron is immediately known and vice versa.
2) Can the photon after scattering be considered as a superposition
of energy-states?
-Edgardo
Hey, folks.
A pretty light read on how quantum entanglement works, starting from first principles without using math but with lots of pictures. Quite good!
http://www.joot.com/dave/writings/articles/entanglement/
Ciao!
T
For more than 70 years, QM advocates have misrepresented Einstein's EPR work. Once it becomes clear what Einstein was really saying, it should be very difficult to stick with Bohr's bizarre interpretation of entanglement.
Among the FEATURE ARTICLES (Cover Story) of the Scientific American...