Quantum entanglement is the 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 not present in classical mechanics.It confusingly says it is a "physical phenomenon", and then says it is a property of how quantum states are described. So it is not a physical property. I removed the word "physical".
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 anticlockwise.
My bigger issue is "quantum entanglement is at the heart of the disparity between classical and quantum physics". This is conventional wisdom, so it is reasonable for Wikipedia to say this, but it is true?
Classical systems obey entanglement, exactly as it is described here. Suppose you have a system of two balls, and you know their total momentum. Assume that momentum is conserved. Then the balls get separated, and you measure the momentum of one of them. You then know the momentum of the other ball, as it is perfectly correlated and opposite. The momenta must sum to the original total.
You can do the same with angular momentum.
So how is this any different from the quantum entanglement? I do not see any difference.
Anticipating your objections, you might tell me that the quantum momentum and spin are not known until measured, or that Bell's theorem puts limits on certain correlations. Okay, I accept all that, but what does it have to do with the definition of entanglement? Nothing.
Or you might say that entanglement is a nonlocal interaction. Spooky action and all that. But that is a big hoax. Quantum mechanics is a local theory.
A more sophisticated objection says that entanglement is a precious resource that can be used for cryptography, teleportation, and parallel computation. Quantum entangled particles have the necessary magic, and classically entangled ones do not.
This objection is harder to answer, as currently billions of dollars are being spent to try to determine whether any such magic exists. Most say yes, but they have yet to demonstrate anything useful from that magic.
Even if such magic exists, there ought to be a way to define entanglement that makes it clearly a quantum phenomenon, and not a classical one.
Quantum systems are different from classical systems. Bell proved that. The uncertainty principle is different, and so are certain correlations. But I don't see how entanglement is any different.
Lenny Susskind and others have been saying that wormholes and entanglement are the same thing.
Almost a century ago, Albert Einstein realized that the equations of general relativity could produce wormholes. But it would take a number of theoretical leaps and a “crazy” team of experimentalists to build one on Google's quantum computer. Read the full article at Quanta Magazine:The idea seems to be that if entanglement and wormholes are the same thing, and quantum computers use entanglement to do super-Turing computations, then there should be some wormholes hiding inside a quantum computer. Seems like a joke to me, but I did not read the details.
Update: Peter Woit writes:
The best way to understand the “physicists create wormholes in the lab” nonsense of the past few days is as a publicity stunt ...I used to think that Physics had higher standards than other sciences for truth and professionalism. Apparently not.
I’m hoping that journalists and scientists will learn something from this fiasco and not get taken in again anytime soon. It would be very helpful if both Nature and Quanta did an internal investigation of how this happened and reported the results to the public. Who were the organizers of the stunt and how did they pull it off? ...
his claims in the Quanta video that the result of the Google quantum computer calculation was on a par with the Higgs discovery. Does he really believe this (he’s completely delusional) or not (he’s intentionally dishonest)? ...
Peter Shor says: It seems to me that the string theorists and “it from qubit” community seem to have this unwritten rule that they don’t criticize other members of this community in public.
I thought you’d be interested to know that the “wormhole created in a quantum computer” story is now being covered in some far-right-wing media. I won’t name them here (they’re very far-right sites, not sure if you’d allow a link here), but they’re essentially saying “isn’t this manifestly stupid? See? Why should we believe scientists when they publish bullshit like this?” and essentially use the story to argue that scientists and science journalists are all a bunch of idiots, hence why should we trust them on vaccines/climate change etc.Here is one such site. It is so disreputable that Google confiscated its domain name. Possibly the most censored site in the world. It just quotes a NY Times tweet, a Google tweet, a Reuters story, and a couple of more tweets, and adds:
This is another consequence of bad publicity stunts like this: it erodes trust in scientists.
This is very obviously fake and it’s goofy that people think it’s real.I agree with that. It is goofy that people think that this research is real.