M1L2d_CQ1.txt

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# Captions for 8.421x module
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Well, then I have a question for you.
I've discussed with you the case that the rotating field rotates
at the Larmor frequency.
But now, I want to discuss the case that the rotating field is
not at the Larmor frequency.
It's at a frequency omega 1, which is faster
than the Larmor frequency.

And the question is now, what will happen to the spin,
or the magnetic moment?
I explain to you that on resonance, the magnetic moment
was just flipping over, rotating, precessing
at the Rabi frequency.
And I want you to think about it for a moment,
and then decide if you go off resonant--
if you drive the system away from the resonance--
with a rotating field which is faster than the Larmor
frequency, what is now the oscillation
frequency of the magnetic moment?

And so the choices are is it larger, smaller or the same?
And this was, of course, compared to the Rabi frequency.

So I've explained to you that the spin flip,
the Rabi flopping or the pi pulse,
and this picture was at the magnetic moment,
thus Rabi flopping rotates-- plus z, minus z, plus z,
minus z, at the Rabi frequency.
But now we drive the system faster than the Larmor
frequency.
And the question is, whatever the magnetic moment does,
is it faster, slower, or does it always
happen at the Rabi frequency?