M1L4a.txt

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We want to talk about non-classical states of light,
which we can engineer in the laboratory
by sending laser light through nonlinear crystals.
And those go by the name squeezed states.
So just to give you the cartoon picture, in our two
dimensional diagram with [INAUDIBLE] probabilities,
we have coherent states, where the area of this x state of p
is over [INAUDIBLE].
But what we can do now is we cannot go beyond this.
This is the fundamental limit of quantum physics.
However, we can take this circle and we can squeeze it.
We can squeeze it horizontally.
We can squeeze it into an elongated vertical shape.
Or we can squeeze it at any angle.
That's what we call squeezed states.

And those states have non-classical properties.
They are important for meteorology.
They are important for teleportation.
So there are lots and lots of reasons why
you want to know about them.
But again, as so often I feel, I cannot convey to you
the excitement of doing squeezing in the quantum
domain.
And many, many physicists, now they
hear about squeezing just in the quantum domain.
But I wanted to start with classical squeezing.
Classical squeezing-- I will actually
show you a video of an experiment
of classical squeezing.
You can see squeezing with your own eyes.
But this is just sort of to set the stage to also get
a feel of what squeezing is.
And then we do quantum mechanical squeezing.

But maybe tongue in cheek, I would
say since classical harmonic oscillator and quantum harmonic
oscillators have a lot in common,
the step from classical squeezing
to quantum mechanical squeezing is actually rather smaller.
Well, it's nice to squeeze light.
It's nice to have those non-classical states.
But the question is, how can you detect it?
If you can't detect it, you can't take advantage of it.
And the detection has to be phase coherent.
I will tell you what that is.
And it goes by the name homodyne detection.
And finally, we can take everything
we have learned together and discuss how in the laboratory,
teleportation of a quantum state is done.
OK, so nice teleportation scheme.
And I want to use that as an example
that the language and the concepts I've introduced
are useful.
So concepts like squeezing operator,
a displacement operator-- those methods
allow us then to, in a very clear way,
discuss schemes which lead to teleportation.
So that's the menu for today.