34 08 June 2012 11:43PM

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Comment author: 10 June 2012 06:53:28PM 3 points [-]

Well, I don't know that I need to point you to arxiv, because I can describe the process in two sentences. Take a beam of electrons and pass it through a magnetic field which splits it into two beams, one going left and one going right. The ones which went left are spin-left, or to put it differently, they are spin-up with respect to the left-right axis; conversely the ones that went right have the opposite spin polarisation on that axis. Now rotate your axis ninety degrees; the electrons in both beams are in a perfect up-down superposition with respect to the new axis. If you rotate the axis less than ninety degrees you will get a different superposition.

Comment author: 10 June 2012 08:31:55PM *  1 point [-]

describe the process in two sentences.

Well, that's helpful, but of course, I don't know how you know that the electrons have such and such spin or what superposition has to do with anything. Neither could I reproduce the experiment (someone competent could, I'm sure). Maybe there was a first experiment where they did this and spin was discovered?

EDIT: anyway, I'm tapping out of here and will check out the sequences. Thanks All

Comment author: 10 June 2012 10:27:03PM 4 points [-]

I don't know how you know that the electrons have such and such spin

Electrons have both electric charge and spin (which is a form of angular momentum), and in combination, these two properties create an intrinsic magnetic moment. A magnetic field exerts torque on anything with a magnetic moment, which causes the electron to precess if it is subjected to such a field. Because spin is quantized and has only two possible values for electrons (+1/2 or -1/2), they will only precess in two discrete ways. This can be used to separate the electrons by their spin values. The first experiment to do this was the Stern-Gerlach experiment, a classic in the early development of QM, and often considered to be the discovery of spin.

Comment author: 10 June 2012 10:58:58PM 1 point [-]

Thanks.

Comment author: 10 June 2012 07:20:42PM 0 points [-]

That was four sentences! D:

Comment author: 10 June 2012 07:39:16PM 2 points [-]

Four is equal-ish to two for large values of two, at least in the limit where four is small. Besides, the last sentence is a comment, not a description of the process, so it doesn't count. :)