Tuesday, May 24, 2011

The most precise measurement of Planck's constant

Compared to some fields (e.g. biology, high energy physics, philosophy, history, movies, historical theology) I think most Wikipedia articles on condensed matter physics and theoretical chemistry are sporadic in quality. It would be wonderful if someone took the initiative and time to improve them. I keep trying to encourage students to do this but not succeeding. But, that is another story....
The actual purpose of this post is just to highlight some of the actual content of a really nice entry on the Magnetic flux quantum, [h/2e] which states:
The magnetic flux quantum may be measured with great precision by exploiting the Josephson effect. In fact, when coupled with the measurement of the von Klitzing constant RK = h/e2, this provides the most precise values of Planck's constant h obtained to date. This is remarkable since h is generally associated with the behavior of microscopically small systems, whereas the quantization of magnetic flux in a superconductor and the quantum Hall effect are both collective phenomena associated with thermodynamically large numbers of particles.
This point is also stressed and discussed at length in Bob Laughlin's book A Different Universe which this blog contains many quotes from.

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