M5L25ja.txt

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Let me make just a side remark.
Maybe some of you remember when we went to cavity QED,
we had just proudly quantized the electromagnetic field,
and we discussed the vacuum Rabi splitting.
And I told you that the vacuum Rabi splitting is if you have--
if the cavity is not empty but is filled with n atoms,
because of the matrix element of the [? a ?] [? a dega ?]
operator, you get an enhancement of the vacuum Rabi splitting
which is square root n then photon number.
But then I showed you the important first observation,
the pioneering research at Caltech
by Jeff Kimble and Gerhard Rempe.
And they didn't vary the photon number,
they varied the atom number.
And when they had more flux in the atomic beam,
the Rabi splitting became larger and larger.
Well, we've just learned that, when
we have n atoms, that the matrix element for emitting the photon
is square root n times enhanced.
So if you put n atoms in a cavity filled with little n
photons, the vacuum-- the Rabi splitting between the two modes
has square root n plus 1 in the photon number,
and square root big N in the atom number.
And so, the effect I've shown you
in the demonstration of the vacuum Rabi splitting, at least
the scaling with the atom number, this was actually--
can be understood as a superradiant effect.