Re: POLARIZATION

[brian whatcott <inet@intellisys.net>]

At 17:50 6/16/98 -0700, James Mclean wrote:

> If I understand Brian, he is thinking this:
> Photons have a spin of either +1 or -1.  Presumably these correspond to
> right-hand and left-hand polarization.  Therefore these are 'more basic',
> and you can only get linear polarization by combining 2 photons (one of
> each type).
>
> If I am correct, then what he is forgeting is that in the quantum world,
> there is no need for a given particle to be in an eigenstate of any
> particular spin operator.  A single photon can be (|+1> + |-1>)/sqrt(2);
> i.e., it still has total spin 1, but it's spin component is indeterminant.
>
> It's sort of what Leigh was cautioning against, but in reverse.  Rather
> than taking components of a photon to be real, it's missing some component
> combinations that *are* real.
>
> -- 
> --James McLean

James is flattering me unduly to suppose that I forgot some quantum 
characteristic that in fact I never knew.
 I recall that many unlikely features of particles at the quantum
level have in fact been experimentally validated.

 Hence, one should be able to say then that a device capable of 
individual photon production should be able to pass a photon through
 a selector of linear or left helical or right helical waves with 
equally high probability.

Assuming that this is already demonstrable, I wonder about the 
description given earlier that a photon's spin direction is either 
parallel or antiparallel to its direction of propagation.
 Does James believe that polarization equates to spin?
 If so, this seems to prescribe preferred polarizations.

With thanks for the interpretations

Brian Whatcott