Re: quantum of magnetic flux

["John S. Denker" <jsd@MONMOUTH.COM>]

At 06:11 PM 3/8/00 -0500, Chuck Britton wrote:
> Back in October someone asked where I got the idea that magnetic flux
> is quantized.
> I had been under the impression that it was 'common knowledge'.

Alas, common sense is less common than common nonsense :-)

> Well, maybe I am wrong, but if so, the Phys.Rev. Focus is wrong too!

Phys Rev is not wrong, because they are talking about quantization of flux
in coherently-conducting rings.

OTOH the bold statement (Mon, 4 Oct 1999 15:38:09 -0400) that
>Flux, measured in Maxwells HAS a quantized minimum value.

is just as problematic now as it was back in October, for the reasons
explained at length back then.

One new wrinkle:  Until recently, the only way to create a
coherently-conducting ring was to use a superconductor.  The work reported
in the 6 March Phys Rev used a nonsuperconductor;  they just made it so
pure and so small that the electron wavefunction could maintain
coherence.  In such a system, the quantum of flux differs by a factor of 2
from the one that applies to superconducting rings.  This is further
evidence that the "quantum of flux in a ring" is a property of the ring,
not a property of the electromagnetic field _per se_.