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."

Comments

spin it up

[MrSquirrel]

So they can control the spin of a single electron? That's pretty neat, definitely sounds like they're making progress on a quantum level of getting closer to the reality of a quantum computer. I'd like to know how they know the electron is spinning -- I'm not questioning their work, I just can't think of a reasonable way to measure how you were controlling the spin.

Hopefully we won't see this applied to spinner rims anytime soon (actually, we wouldn't be able to see it at all, so who cares?!).

Amazing.

[radarsat1]

This is really incredible news.
One thing -- there is no mention in the article about how _long_ it takes to read the electron's spin. It would be interesting to know. It says they simply have to see whether the two electrons can be placed next to each other. How is this done and how long does it take? I would assume for a quantum computer to be useable this method must be able to be executed quite quickly. (Maybe the speed isn't important?)

Electrons do not spin around an axis

[emil10001]

From the Article at http://www.tudelft.nl/live/pagina.jsp?id=4b3e55d0- 1a34-4388-b3ca-acbe48c87696&lang=en:

An electron does not only have an electrical charge, but it also behaves like an ultrasmall magnet. This is caused by the spinning of the electron around its axis, also called 'spin'.

Electrons do not move about their axis, the spin is a measure of the magnetic angular momentum, if memory serves from quantum physics. Also, no, electrons do not only have two directions to spin, their spin can be in any direction, but only measured spin up or spin down with respect to a single axis at any time. This is based upon the fact that in the Schrödinger equation the operators don't commute for the eigan functions. Put simply, that means that if you measure the spin once in the z direction and obtain an answer, then in the y, and again in the z, you will end up with a different value.

I would also like to know how they are controlling the spin in every possible direction, and effectively measuring it. Because unless the laws of physics have changed, they can still only measure spin up or spin down.

Re:Electrons do not spin around an axis

[brunascle]

the article doesnt go into enough detail, but i dont think it's claiming they they're controlling or measuring all the axes at the same time, but just that they're not limited to a single axis. that would seem to make sense, if they're planning to use an electron for a single bit (up=1, down=0).

i have some other questions though: for one thing, are they realling claiming they can "lock up" an electron? doesnt that imply that they know both its location and momentum (stationary) at the same time?

Re:My feeble attempts to understand quantum physic

[althai]

No, information still cannot be transmitted, as other posters have mentioned. They can control the spin of one of the entangled electrons, but once they do, the electrons are no longer entangled. Science-fiction authors are fond of using "entanglement" to defeat speed of light limitations on communication, but it doesn't actually work (at least, not according to current theories, which are unchanged by this experiment).