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Monday, 12 November 2007

Doh! The Quantum Zeno Effect

"Doh!" as in, beaten to it again!

A long time ago (though I doubt as far back as 1977) I humorously proposed what is apparently called the Quantum Zeno Effect - a way of inhibiting state changes by obsessive observation.

I say humorously because I was proposing it as a way of handling nuclear waste - and one that is not as far as I can see at all practical (Worried about radioactive decay? Just keep an eye on it - and it won't! How one could appropriately "observe" a large mass of diverse composition I wasn't - and still amn't - sure).

And, as this is the way of things, I find out today (thanks of course to the New Scientist article here - subscription required to read the whole article online) that George Sudarshan and Baidyanaith Misra of the University of Texas apparently described this phenomenon way back when I was 16. It's since been established experimentally too.

The reason it works is that for small t, the probability of a transition is proportional to t squared...

I found a nice demonstration of the idea here (a pdf of a presentation by Wayne Itano of NIST) but, for those of you impatient for the Technical Stuff the maths bit looks like this...

So, there you have it: a watched superposition never decays.

(Of course in practice you can't make the absolutely necessary infinite number of observations to completely stop decay, but you ought to be able to slow things right down)

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