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"Spooky" Science Points Towards Quantum Computing
Stony Stevenson writes to tell us that University of Michigan physicists have been able to establish an "entanglement" between two atoms trapped more than a meter apart in different enclosures using light. This shows how two different atoms can have a sort of communication, something Einstein referred to as 'spooky action-at-a-distance'. "By manipulating the photons emitted from each of the two atoms and guiding them to interact along a fibre-optic thread, the researchers were able to detect the resulting photon clicks and entangle the atoms. Professor Monroe explained that the fibre-optic thread was necessary to establish entanglement of the atoms. But the fibre could be severed and the two atoms would remain entangled, even if one were 'carefully taken to Jupiter'."
An ansible is a device described in science fiction for superluminal communication. It's usually portrayed as a pair (or more) of devices closely connected, as if separated from a common origin.
I'm looking forward to a day when ansible devices are as common as symmetric key crypto, which will likely be the only way to secure their communications, other than the "conservation of info" already built in to quantum entanglement.
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make install -not war
> a small machine that measures that's designed to react when it an electron comes "de-entangled" That's your mistake. There's no possible way to detect that an electron has suddenly become "de-entangled".
The only thing the machine can measure is the electron's spin in either of two axis. Now, say you measure it in the left-right axis and its spin comes up as left. What do you know now? You do know that if the corresponding entangled particle has been measured in the left-right axis, it would have come up as right. But this does not tell you whether it has actually been measured. There is no way to tell whether the other party has measured their particle. No information has been transferred. You can't violate causality, even with quantum entanglement.
What's purple and commutes? An Abelian grape.
No. You can't transfer information across an entanglement. Faster than light communication is as impossible as it ever was; and causality has not yet been knowingly violated.
What's purple and commutes? An Abelian grape.
Ok, your comment is badly mangled, but I think I get the gist of it and I'll try to explain.
The problem is that we can't currently control what state the two disentangle into, we can merely guarantee that they share a state in common. Special relativity doesn't explicitly deny something happening faster than the speed of light, just data being transmitted faster than that limit. Because we can't determine anything from the two entangled electrons other than they share a common state, we can't actually get any data out of the system, thus there is no discrepancy. There's also the fact that determining if they are entangled is itself a measurement and thus the act of checking for entanglement breaks the entanglement. We can only verify they are entangled by checking after the fact that they both have the same state when we measure them, otherwise there is no way to know if they are entangled or not.
Curiosity was framed, Ignorance killed the cat.
I've said this a few times now, but I'll repeat it: You Can't Transmit Information Across A Quantum Entanglement. (Usual caveats: to the best if our knowledge at the present time).
What's purple and commutes? An Abelian grape.
What's purple and commutes? An Abelian grape.
It's more like you have a bag of blue and red billiard balls, you pull out two randomly without looking at either ball's color, place each in a box and ship them halfway across the world. The two boxes are opened up and observed, and each time one box contains a red ball the other box will always contain a blue ball.
What's even weirder is that in the quantum mechanical world, it's not that your picking two particles that are either in one state or the other with equal probability and it turns out that you always pick up opposite states. Rather it's that you have two particles that are both in both possible states at the same time. When you measure the particle it collapses into one of the two known states, but up until then it is in a superposition of both. And when you do that to one of the two entangled particles, the other particle will also collapse into one of the two states at the exact same time and you will know exactly which one the other particle will be in based on what state your own particle is in.
The laws of probability forbid it!
Before complaining, please know what you are talking about... A quick search on wikipedia would tell you: Einstein received his Nobel Prize for works on Quantum Theory!
http://en.wikipedia.org/wiki/Albert_Einstein: Einstein received the 1921 Nobel Prize in Physics "for his services to Theoretical Physics, and especially for his discovery of the law of the photoelectric effect."
http://en.wikipedia.org/wiki/Photoelectric_effect: The photoelectric effect is a quantum electronic phenomenon in which electrons are emitted from matter after the absorption of energy from electromagnetic radiation such as x-rays or visible light. (...) The photoelectric effect helped further wave-particle duality, whereby physical systems (such as photons, in this case) display both wave-like and particle-like properties, a concept that was used in quantum mechanics. Albert Einstein mathematically explained the photoelectric effect and extended the work on quanta that Max Planck developed.
Quantum mechanics is hard for people to understand because the effects we observe at the quantum level are fundamentally different from our experience with the macroscopic world. Consider a photon's polarization. If you polarize that photon up-down, then with 100% probability, the photon is polarized up-down. If you attempt to measure the photon's polarization left-right, you will discover that with a 0% probability, it has that polarization. So far so good right? If, however, you measure the polarization of the photon at 45 degrees, you now have a 50% probability that is polarized in that direction and 50% probability that is polarized at -45 degrees.
Now, extend this to entangled photons. You entangle two photons that are polarized up-down. You separate the photons by some distance. If you measure the polarization up-down, with 100% probability, you will discover that the polarization is up-down. No information transfered, nothing learned. Why? You already knew that the probability was 100% of being up down. Now, let's say that you measure the polarization at 45 degrees. With 50% probability, the polarization will be at 45 degrees instead of -45 degrees. Again, no information transfered. All you know now is that both particles have the same polarization. If someone else was holding on to the other entangled photon, they cannot know that the photon has "resolved" itself to a particular polarization value after the first photon has been measured. If someone told them the polarization of the first photon, then they could predict the value of the photon that they currently have, but that first requires someone to tell them (at the speed of light) what the polarization of their photon is. Again, no information transfered.
So what is entanglement useful for then? It could be used as a powerful method of sharing a secret. Suppose I give you a cloud of entangled photons. If I don't know anything about the photons, then their polarizations will be completely random. I could then say that each time I resolve a photon's polarization, I will send you a message that I have read the value of the photon. So, I read the polarization of one photon causing its field distribution to collapse to the value I have measured. I then send you a message saying I have read the first value. At this point, you read the value of the corresponding entangled photon. You know that we have the same values, and so we have our first bit of the secret key. If we repeat this process for each entangled photon, we would end up with a random secret key that we both share that has never been sent across the transmission medium.