Slashdot Mirror
Physicists Control the Spin of a Single Electron
jeeb writes "Researchers of the Delft University of Technology and the Foundation for Fundamental Research on Matter have succeeded for the first time in controlling the spin of a single electron in a nanostructure. They are able to rotate the axis to every possible direction and to record it accordingly. This achievement makes it possible to use the electron's spin as a 'quantum bit,' the basis of a (still theoretical) future quantum computer. The researchers have published this scientific breakthrough in the August 17, 2006 edition of Nature."
I know they can measure the field easily... but after reading most of the full article, I wasn't sure how they would measure it while still controlling the rotation (since they were spinning the electron using magnetic fields). Then I finished reading the whole article (after posting of course) and got my answer: "Their approach was to lock up a second electron in another quantum dot alongside the first one and to use it to read out the spin direction of the first electron."
A computer once beat me at chess, but it was no match for me at kick boxing.
Read the press release then repeat after me boys and girls: electrons do not spin; electrons are point (or point-like) particles with **intrisic** angular mommentum. Sometimes we sloppily refer to the intrinsic AM as "spin" but that has nothing to to with an electron spinning around some axis. You'd a thunk the folks at TUDelft would have read the press release before allowing such drivel to be disseminated.
Is it ironic that the crypto word for this post is "nature"?
Folks, electron spin is NOT like the spinning of a ball in "the real world." The electron is not "rotating" per se. From wiki:
"Such particles and the spin of quantum mechanical systems ("particle spin") possesses several unusual or non-classical features, and for such systems, spin angular momentum cannot be associated with rotation but instead refers only to the presence of angular momentum."
jfs
The only thing worse than a Democrat is a Republican.
I once asked a FSU physics researcher (who used to hangout at a coffee house and regularly beat my ass in chess) about quantum entangement. He told me essentially it was a parlor trick and to forget about it. /Don't know the point of this story, really...
OK, we can't really explain the whole entaglement thing without using big words and wave equations, but here's a very close analogy:
Say you have two balls, one red, and one blue. You blindly put them into two identical boxes, and ship one to Pluto. After that's done, you open the box here on Earth and see that it's red. You instantly know the color of the ball on Pluto is blue. What good does that do you? Nothing.
The quantum entaglement is almost the same, except that the balls don't finalize their color until you look at one. But the information is just as useless.
The question of This + Quantum Entaglement is also flawed, you can't have both. If you set the spin of one, you've destroyed the entaglement.
-Ryan C.
That's not precisely true. Of course, some ways of recording the spin will change it, and there are theoretical restrictions, but in theory it is possible to observe the spin without changing it. For example, measuring the spin in a particular axis as up or down will set the quantum state to a pure state of up or down in that axis. If it was already in that same pure state, observing it wouldn't change it. Of course, observing the spin in a particular axis sets it into a pure state, so if it weren't already in a pure state, or if it were in a pure state along a different axis, then you're right that an observation would change the spin.
David
I don't think the electron's spin is the spin you're thinking of. Electrons don't literally physically spin, their spin is a quantum state. There are two possible spins for an electron, and two electrons with different spins can otherwise exist in the same place (ie. the same orbit around an atom). The test they're doing likely tests to see if the two electrons can coexist in one spot, or if one actually "hits" the other.