What is Entanglement: Definition and 869 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.
Is the wave function a "relative" wave (entanglement)
Alice and Bob build a quantum entanglement experiment with the help of a lab technician.
The experiment runs and a quantum entangled pair is created but unbeknown to Alice & Bob the technician puts his own measuring device in the...
Is quantum entanglement unaffected by fields/forces?
Forces = the, yet known, four fundamental forces
i.e. Is quantum entanglement "friction-less"?
Assumption: Anything that is effected by fields and forces can, at the most, interact/move at the speed of light.
Quantum entanglement...
Photon Entanglement Question
Polarize a string of photons vertically. Make the polarized photons into two streams of vertically polarized entangled photon pares. One photon of each pare will go to point A and the other will go to point B. All photons that arrive at point A will encounter a...
Hi,
Lately I've been reading up on quantum entanglement, Bell's inequality, and EPR experiments. My question is fundamental, but I'm asking it here because I haven't yet read an explanation that answers this question (that I recall).
Take this typical description of what goes on in an EPR...
Now please forgive the question, and thank you in advance for your patience...
I am a little confused by the wavefunction collapse upon observation thing (yes, thing is a technical term :-)...
So, is it the same as, say I have a 'penny splitter', i.e. 'beam splitter'...I shoot my penny...
Say we have a system consisting of two electrons, traveling freely, that are not initially entangled, either in spin or in position-momentum.
Then, because of their electric fields, a photon is emitted and absorbed between the two electrons.
Are the electrons now guaranteed to be at least...
How stable/fragile is Quantum Entanglement? with respect to time, space and various events.Space - We know that experiments have validated QE working across say 150 kms and it is generally believed that they can work across very large distances. Does gravity effect QE over large distances?
Time...
Clearly, I am a newb at this. However:
I was reading a bit on qubits and quantum entanglement and -- though I know that QM has no analog to classical mechanics -- the general concept seems to be: two particles interact and become quantum entangled, and then have non-local ties to each other. To...
how does/would LHV (local hidden variables) theory explain the phenomena of:
1. quantum entanglement swapping (where Alice and Bob never meet, and Charlie/Victor is still able to entangle their photons)
2. two-photon interference without the photons ever meeting at the same time-space/place
In regards to measuring two photons in the 45/135 basis using 22.5 wave plates and PBS orientated in the H/V basis:
Is it with the entanglement |H>|V> - |V>|H>, with the wave plates:
H -> 45
V -> 135
so
|45>|135> - |135>|45>
And back again using a PBS:
|H>|V> - |V>|H>
So getting |H>...
All definitions of entanglement, that I have encountered, were expressed in the language of non-relativistic QM.
Suppose a free, massive particle decays into 2 other massive particles. The 2 new particles would be entangled in linear momentum. Can QFT define that type of entanglement? Any...
I suppose the meta-question is: Where do I read about this? Engineering major, not physics. Worked through Penrose's book until the tensor calculus on manifolds chapter and then sank without a trace. The popularized descriptions of quantum physics are hopelessly incomplete and as Feynman...
In regards to the attached image;
If the input photons were, for input b = photon #2, and for input c = photon #3, where:
photon #1 and #2, and #3 and #4 are entangled as |H>|V> + |V>|H>,
for the outputs:|H>(b’)|H>(b’) - |V>(b’)|V>(b’) + |H>(c’)|H>(c’) - |V>(c’)|V>(c’) + H(b’)|V>(c’) -...
Good afternoon. I am wondering if quantum entanglement could be created between two thermodynamically isolated Bose-Einstein condensates of the same atom produced at the same time in close proximity. Due to the similarity of the systems' mathematics regarding their quantum states (wave...
Question: Do we really need to spend too much time on Bell's theorem/test when there are numerous/easier proofs of quantum entanglement?
The numerous/easier proofs are: - Almost all experiments in which two photons are generated via
a) SPDC (Delayed Choice Quantum Eraser, Mach–Zehnder...
I was hoping if someone could briefly explain entanglement purification. I’ve read http://www.lsr.ph.ic.ac.uk/~plenio/cp394311998.pdf , but because I’m not mathematically inclined most of it isn’t sinking in.
What I gather is in the beginning you share two entangled states, and one of the...
Hi,
I've been reading some stuff about quantum entanglement and I stumbled upon an article talking about a delayed choice quantum eraser experiment using parametric down conversion. I was wondering if it was possible to communicate a signal through to the other side faster than light...
When I read about entanglement it is described as the singlet state two particles (or eventually even molecules) are in after interaction with each others or due to a decay. Put in that way it does not sound difficult to do. Just let two particles scatter with each others and we should have an...
Physicist say "Quantum Entanglement is when you place 2 electrons together.
They Vibrate in Unison.
When you take them across the galaxy if you "jiggle" one, The other also "jiggles"
Physicist say" however it does not transfer any meaningful information"This is a EVIL way of speaking.
Why...
I'm a new poster; I hope don't violate rules or policy.
Am I wrong, or is the rule essentially that a particle isn't finished interacting with the last particle on it's world path unless and until it interacts with a third? This isn't what I might have guessed about physical continuity, but it...
The Pauli exclusion principle: is the quantum mechanical principle that no two identical fermions (particles with half-integer spin) may occupy the same quantum state simultaneously
Quantum entanglement: the type of interaction is such that each resulting member of a pair is properly...
I do not know a lot about physics, however, I was wondering if anyone would know, now that they think something can travel faster than the speed of light, would that solve the entanglement issue in quantum mechanics or at least the problem Einstein had with it? Or how two particles would be...
I already asked this question on physics.stackexchange.com, but did not get the desired response. I am interested in the opinion of your community.
Picture an entangled pair of spin 1/2-spin particles with total spin 0. In the diagram, particle 1 of the pair is moving to the left (-y), and...
hi all
i have two questions.
1. Quantum entanglement is observed experimentally. But how can that be. Does not Quantum decoherence effect it from being observed?
2.The general notion is that M String theory if proven is theory of everything. But without explaining entanglement how does it...
Hello,
I can understand only the basic principle behind quantum entanglement. Do you guys know of the mechanism by which it works? I understand that there is no information being transferred between particles that react under entanglement. So what then is the hypotheses as to how one particle...
Homework Statement
A system in a state \frac{1}{\sqrt{2}}(\left<\phi\right| + \left<\psi\right|) undergoes an interaction with a second system (which is initially in \left<\alpha\right|) and ands up in an entangled state \frac{1}{\sqrt{2}}\left(\left\langle\phi\right| \otimes...
Hi there,
If we set-up an experiment for entanglement swapping, the two entangled pairs of photons are:
Group 1: A, B
Group 2: X, Y
Take B and Y and perform a Bell-state measurement on them.
Obviously A and X are now entangled. But for this to occur, must B and Y have no definite...
the entangled photon was sent 10 miles i believe, doesn't matter.
my question is, once the polarization change is viewed on the receiving end, can the observation of the entangled photons ppolarization change be viewed more than once per entanglement?
or could the two ends essentially send...
That quote is from this article..
http://www.physorg.com/news/2011-05-vienna-physicists-quantum-twin-atoms.html
I thought that's exactly what entanglement meant. Can someone please explain entanglement better then? I am miss understanding Schrodinger's cat experiential.
Hi there,
I was looking through Zeilinger's "Dance of the Photons" where I re-read the section of three-photon entanglement. If one photon is measured in H polarisation, the other two take on H - likewise with V polarisation.
What I find interesting is if we measure one photon and its H...
How and where is quantum entanglement orchestrated? Does it require a deeper, non-spacial level of existence where the distance between entangled particles is irrelevant?
Is entanglement still considered "spooky"?
Even now in 2012, you often hear the phrase "spooky action at a distance" regarding entanglement. Is this just a popular-science cliché, or do some physicists really consider EPR effects (e.g. Alice sees spin-up, therefore Bob must see spin-down)...
Hi
Do the experts on this forum think that it is possible for there to be special particles scattered throughout the volume of a living human brain which together form a single permanent quantum entanglement which lasts at least as long as the lifetime of the brain? If yes, what do you think...
Hello everyone,
I have a basic understanding of quantum entanglement. One thing I don't understand is the following: For particles to be entangled, is it necessary to produce the entanglement via whichever means, or are all particles entangled to another particle to begin with? By the latter, I...
If we produce a three-pair of entangled photons, and send two of them towards polarising beam splitters, and one towards a vertically aligned wave plate - according to QM we need to describe the photon as being in a superposition of V and H when they hit the beam splitters, but when the photon...
As an amateur, I have been reading about the EPR argument, and afterwards Quantum Entanglement recently. Then I thought that the bound between two particles is only the applicability of a physical rule of everyday reality. For instance, the momentum or energy must be preserved at all times, so...
I'm trying to follow the logic to the quantum theory of the entanglement of light. I'd like to ask a question about one of several problems I'm having with the entanglement.
If:
Photons (Light) have orthogonal electric and magnetic waves.
And:
In discussions of polarization of light for...
Is Energy the "Glue" of Entanglement?
Forgetting the case where one particle becomes 2 particles, can entanglement between two, originally independent, particles occur without some kind of energy exchange between them? Is energy the "glue" of entanglement?
Hi,
I was reading some novice stuff about quantum entanglement and I was wondering
if entanglement occurs in either of these two scenarios:
1. electron and positron entangled as a result of being created by a photon passing over a heavy nucleus
2. two free electrons entangled with...
A question came up about entanglement and I've only studied very little QM so far, so I went to wikipedia to see if I could become any wiser and they had an example on photon entanglement which was quite straight forward (though the whole page lacks sources =[ ). The example shows that if you...
It is said nothing can escape the Event Horizon, not even light. How about an entangled pair that is inside the event horizon and outside it. Would they still be entangled such that they still form correlations?
I'm a bit confused about entanglement with regards to quantum computing. I'm not an expert by any means, but I've been reading around about quantum computing and was confused about something.
I've read that, you can't directly observe a qubit, because if you do the wave function will collapse...
Two or three years ago there was an interview in a science journal with a physicist who had worked on the large hadron collider. The interviewer asked what he wanted to do next,and he replied that he'd like to do some experiments in quantum entanglement but had no funding. Apparently donations...
First time poster:
Is there any math out there that prohibits the following scenario from taking place:
Alice and Bob are entangled. Is it possible to detect that Alice is entangled, without measuring Bob and without destroying the entanglement (or causing decoherence)?
Note: I am not...
Article: "Faked States" mimic quantum entanglement
Does anyone know where to find a copy of this that isn't pay-walled?
http://physicstoday.org/resource/1/phtoad/v64/i12/p20_s1?isAuthorized=no
From my understanding of it thus far (and please pardon me if this is the result of a novice perspective of the subject):
a) if a pair of particles are entangled they are known to be in the same state or exactly opposite states
b) changes to the state of one of the two particles introduce...
Hello all,
I know "quantum entanglement" is real, in some sense. I know that if we entangle two particles their spin, for instance, is closely related. Especially spin entanglement has enough evidence, yet it is also easy to explain using a hidden variable.
Hence I wonder: what other...
Let me see if I understand this correctly, please critique. Say, 6 players are playing a game of hold em. This means that in a randomly shuffled deck, two cards will be dealt to each player totaling twelve cards. Say no player has observed their cards. At this point the cards are in...