M5L22e.txt

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So here we have now a situation where the photon field
has a random phase, because we did not-- we lost the phase
information of the laser beam when we put
the atom into an excited state.
And you may now ask, what is the origin of this phase
uncertainty?
And at least the qualitative answer
is it's vacuum fluctuations.

You can take the concept of vacuum fluctuations
a little bit further-- and just mentioning it
but I will not work it out-- but the fact
that the phase of these photons, which is random,
is somewhat associated with vacuum fluctuations,
you can address this question when you talk about two atoms.
So we have two atoms.
We excite them both with our [? pipals ?] into an excited
state, and then as time goes by, we
will have atoms which create photons.
And at least as long as the atoms
are well localized within an optical wave lengths,
you could play with the idea that if they're
vacuum fluctuations, maybe the two atoms will see
the same vacuum fluctuations.

And therefore, indeed you will actually observe correlations
in the relative phase.
So if you measure the phase of the light emitted spontaneously
by the two atoms, you will find a correlation
which is caused-- which is due to the fact
that-- I'm waving my hands here--
but that the spontaneous emission was triggered
by the same random vacuum fluctuations.
So from the absolute phase will be completely random from time
to time, but the relative phase will be correlated.
So but what we're talking about here
is correlations between two atoms.
We want-- we will talk later about superradiance,
and maybe this will make it much more
clearer what it means if several atoms emit spontaneously
together.