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.
"Four Handed Entanglement" - With a Catch!
http://news.sciencemag.org/sciencenow/2013/05/physicists-create-quantum-link-b.html?ref=hp
Can we start an Office Pool on who gets the Nobel and when? This is just great stuff!
CW
Can somebody clear the fog in front of my eyes: how can a Hamiltonian describing free fermions have a ground state with non-trivial entanglement? My reasoning is: we can build the ground state in the independent electron approximation (which is now exact), hence it is a product state in the...
I'm not all that learned in Quantum Physics, but I read about this, and it piqued my interest.
I read that the minimum speed that's been found for Quantum Entanglement, according to research done by Prof. Juan Yin and colleagues at the USTC in Shanghai, is 10 000c. This doesn't rule out the...
Quantum entanglement (information transmitted !)
Hello,
In all information I see about quantum entanglement, it's stated that nothing travels faster than light, because no information is transmitted.
I believe that in in the experiments done, you can't detect the exact quantum state of a...
I apologize in advance if this has been asked many before, but I didn't see anything that answered my question on the first page of threads.
Take, for example, an isolated subatomic particle which breaks down into two entangled particles.
From what I've read, each of these two particles...
entanglement at cosmic distances possible??
Warning, crazy question from uneducated human :-) Patience required.
Ok, so say there is an Alien civilization far away, and they and we both 'see' a event, say a supernova.
Is there a way that the photons WE recieve, and the photons THEY...
We have two concepts - discrete and continuous
While the concept of discrete tends to be associated with quantum mechanics;
Is quantum entanglement a resource that hints at continuity even when (the entangled particles are) separated in time-space?
Hello.
I have a question suppose we have two entangled electrons , now we take them a sufficiently large distance away from each other so that the EM (light) wave would have to travel a certain distance/time.When one electron is measured at one place and the other at the other place they botch...
How do fermions, which have vast amounts of empty space, know not to occupy the same space as another fermion? Do physicists say that the two fermions become entangled and that is what enables them to be "aware" of the "existence" of the other fermion? Is entanglement used as an explanation...
I posed these questions via email to a few actual physicists, with the only responses received coming from those that admit to not fully understanding the subject matter. And maybe it's too simplistic for the others. I've read countless articles but haven't come across satisfactory answers, at...
I don't like the way Wiki describes entanglement. Here is my own definition. Tell me if it is in essence correct. If I have left out an important detail please let me know
objects are entangled if and only if by changing the property of one object one instantaneously changes the property of...
This question may have been posted before, but I didn't have much luck finding it. We can't know the momentum and position of a particle at the same time, but if one were to entangle two particles (I.e. photons), wouldn't it be possible to measure one quality on each and thus deduce both the...
Hey everyone, I'm a second year undergraduate student in aerospace engineering and I've been learning a bit of quantum mechanics for the past few weeks, for recreational purposes.
I've been following this textbook: http://www-thphys.physics.ox.ac.uk/people/JamesBinney/qb.pdf
On pages 40-41...
Trying to understand coherence and entanglement and have some questions:
1. Do incoherent photons interfere?
a) Single particle interference through double slit
b) Multiple photons through double slit
Is it that the interference pattern in the above cases is not a clear fringe pattern...
once entangled photons are created (via say SPDC or quantum dots etc) ...how long does the entanglement last?
there is so much noise in the environment
so many things the entangled photons would interact with,
so many ways to transfer/exchange momentum with the surroundings
My understanding of wave-functions is close to zero, pardon me if the questions don't sound proper.
1. Do we have wave-function usage to describe a) Coherence and b) Entanglement?
2. Has a (mathematical/conceptual) way been developed to show the complementarity between both (a & b) via...
During the creation of entangled photons (say via SPDC as described, for example, at the bottom of this post):
Do/can we also get photons that are say 60/40, 70/30 etc? ..if we remove/adjust the filter etc...
i.e. the entangled photons are not exactly half the energy
but
one of the entangled...
I am new to this forum, and posting in forums in general, so this is a slightly strange experience for me. I would like to kindly and respectfully request everyone's cooperation, and if those posting would be respectful in their answers.
I was recently reading through an article on an...
Superluminal signals using quantum entanglement
Please consider this thought experiment. Would this provide a means for communicating faster than light or is there an error somewhere in it?
SUMMARY: Person B can instantly know whether or not Person A did measurements on his particles by...
We know that single particle interference is effected by certain kinds of obstruction.
Is there any effect of Obstruction when placed between two entangled particles?
Single particle interference and quantum entanglement may not have that much in common, however just wanted to check.
Understanding conservation of energy during generation of entanglement.
In the experiment for generation of entangled pair of photons via SPDC
Single photons are struck on a BBO crystal.
In about 1 in a trillion of such collisions, two photons emerge.
Questions:
1. Is the...
So I watched this video talking about now slices, and how it seems that across vast distances of space, movement can affect what is actually the now of places far away.
https://www.youtube.com/watch?v=
This seems to be in direct conflict with what I've heard about quantum entanglement...
The results of measurements of phase entangled particles together with Bell's theorem provide pretty convincing evidence that the Universe contains non-local interactions.
Yet I'm lead to wonder.
Let's imagine the usual idealised experimental scenario, where there is an emitter of...
Hey all,
I have what I think (hope) is a relatively quick pair of questions regarding entanglement of fermions and bosons. First, am I right in saying that if two fermions are in the same position-state, they will necessarily be entangled? My reasoning here is just that if their...
As I understand it wavefuctions of individual particles are incomplete descriptions of a system because ultimately a wavefunction describes a system and cannot be reduced to individual particles (which would exclude things like entanglement).
So the only way to have a good idea how a system...
I don't have a good grasp of "spin along axis" topic, so pardon my dumb questions:
1. Does a photon/electron have a different spin across each of the 3 axis?
i understand that the spin of an electron/photon is not the same as that of, say, a ball
2. Gravity can distort time-space (and hence...
I came across this phenomenon during my undergrad quantum mechanics studies, but haven't delved into it very much.
I'm interested to know though, if theory for quantum entanglement is complete?
Everyday analogy why hidden variables can’t explain entanglement
I tried to come up with an everyday “obvious” analogy that explains why a hidden variable theory cannot explain quantum entanglement.
Here’s the story: There are two guests and one moderator on a stage. The moderator...
Understanding energy transfer during the creation of entanglement
Below is an attempt to understand the energy transfer process during entanglement, please correct where required.
Broadly/conceptually speaking:
There are two kinds of 'energies’ associated with a photon.
1. The photon...
What is the effect of differing frames of references between entangled particles?
For example, let's look at the below scenario:
Photons are entangled in Alice's frame of reference on say earth.
Photon B is put on Bob's spaceship that travels at say 95% the speed of light.
The other photon A...
All,
I'm new to the forum and registered as I have a scenario which has me confused (not difficult!)
The scenario goes as follows and involves:(and please correct me if anything I'm suggesting is incorrect)
-person A journeys to a nearby star and travels near the speed of light...
Citing a recent post from Dr. Chinese, it seems like quantum entanglement experiments are showing something beyond the current standard model.
https://www.physicsforums.com/showthread.php?t=637454
If particles can be entangled to other particles that only existed in the past, it seems that it...
Refer to the experiment below:
Trying to understand this phrase/sentence: "Entanglement after the photons no longer exist"
What is being entangled if the photons no longer exist?
Victor can entangled the two photons but Alice and Bob's photons are destroyed, so how can they be entangled...
Consider me physics illiterate since my last class was advanced placement physics in high school (over 20 years ago). I am trying to understand what the title says, How does quantum entanglement, string theory, and the BB fit together?
Skipping to the meat of the subject, everything revolves...
I have posted many times that entanglement between photons that have never existed at the same time is theoretically possible under QM. Now an experiment has been performed that demonstrates this. The technique uses entanglement swapping.
Photons 1 and 2 are created as an entangled pair...
Say you have two cards: an ace of spade and a king of spades. You put one in your hand without looking at it, then you travel 10 km away. You look at the card, it's an ace of spades and you know instantaneously that the other card 10 km away is a king of spades. Information has just traveled...
Because the universe started as a point of almost infinite density, wouldn't that mean that every particle in the universe interacted with one another while in that state, crammed together, thereby causing all the particles in the universe to be entangled, including those particles that created...
This looks more like a relativity question, so let's post it here. I try to keep it short.
Alice and Bob approach each other, synchronize their clocks when they meet, then drift away from each other with relative speed 0.8c. No acceleration involved here. There is an entangled particle, Alice...
Okay, I have the following scenerio (attached picture).
The inputs for path b and c are two photons. both photons aren't entangled with each other - they're entangled to other photons. Before the beam splitter there is a wave plate that converts the photon into the 45/135 basis.
So what we...
The quantum physics forum is full of questions about why entanglement can't be used to signal superluminally.
My question is this: do these questions usually still make sense if we replace entanglement by classical correlation? For example, I can send Alice and Bob each a random bit but with...
when one entangled particle is measured and its state known the other particle of the entangled pair is described instantaneously collapsing into the same state. What exactly does this mean? does this mean zero time for the pair to take on the same state? I thought the minimum amount of time you...
Q1: If every atom has to adjust their energy levels according to every other atom in the universe, does that mean that any given single atom has its interior invaded by a catalog of energy states from every other atom in the universe? And only after accounting for all the energy states that...
Why is coherence and entanglement complementary?
Lets take the case of a pair of entangled photon.
there is very little coherence between the entangled photons.
when we try to improve the coherence; the (degree of) entanglement starts to reduce.
why does that happen?
Does it have...
Let's say there's a ship that's traveling at a sufficient velocity from the earth, such that the time is dilated for the ship by an arbitrary factor 10,000. If the ship has an entangled particle connected to another entangled particle on earth, and the entanglement is broken by observation, is...
I am not a physicist and really do not have any formulas or basis, it is merely a concept that occurred to me and I was curious if it had been thought of or if it was even possible?
Conceptual question: Could quantum entanglement be used in conjunction with a photon, to be able to move...
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...