M0L1b.txt

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# Captions for 8.422x module
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In this course, I want to present to you
the concepts behind many of the major advances in the field.
So over the years, quite often a topic was added to the course
because I felt, hey, it's getting really exciting.
That's what people want to do in research.
That's what graduate students want to do here.
And then this subject was added, and other subjects
were dropped.
I know in the '90s, I was teaching aspects of laser
cooling, subrecoil laser cooling, which
was the latest excitement.
This year, I may mention it for 30 seconds.
So the course has evolved.
It wants to stay connected to what is exciting, what is hot,
and what prepares you for research at the frontier.
8.422, the second part of the two-course cycle
in the graded course in E&M physics
is somewhat different, not radically different.
But it's somewhat different from part one, from 8.421.
First of all, 8.421, 8.422 can be taken out of sequence.
We alternate between EM-01 and EM-02.
And whenever you enter MIT, you're probably
in your second semester, take ever be offer.
So let me ask you, who of you has taken EM-01?
Yes, statistically, it should be about half of the class.

It can be taken out of sequence, because that's the way how
we've structured it.
But sort of to give you one example
is, in 8.421, you really have to learn
about hyperfine structure.
You have to learn about atoms.
You have to learn about Lamb shift and all that.
So you have to learn what all these atomic levels are.
And here in that course, in 8.422, I will say,
here's a two-level system.
And then I run with it, and we do
all sort of entanglement, manipulation of two level
system.
So it helps you if you know where
those two levels come from.
But you don't really need the detailed knowledge
of atomic structure to understand that.
So this is why the different parts of the course
are connected but, in terms of learning the material, somewhat
decoupled.
I've spoken to many students who said
there was no problem in starting with 8.422.
The only sort of critical comment I've heard
is that taking 8.422 first and then 8.421 is anti-climactic.
You see all this excitement in the modern physics.
And then eventually, you have to work on the foundation.

Yes.
Prerequisites for this course-- the course announcements
said 805.
It is actually 805 and 806.
The main part of 806, which we really need here
is perturbation theory-- time-independent,
time-dependent perturbation theory.
And this is usually covered in 806.
However, I've had students who took the course without 806.
If you're really determined and want
to acquire certain things by self-study,
you can follow this course.
The topics we will cover include QED.
I really want to talk about light-atom interactions
from first principles.
Sure, 95% of what we are doing is just
done by using we have a matrix element, which may
be the dipole matrix element.
But you really have to know what are the approximations, what
are the conditions which lead to the dipole approximation.
And I want to do that from first principles,
and we do that starting on Monday.
The discussion of light-atom interaction has two parts.
One is the simple part, excitation and stimulated
emission, because this can be simply described
by unitary time evolution.
And you can do a lot, if not everything,
by using Schrodinger recreation.
Things get much more complicated and richer
if you include spontaneous emission or, more generally,
if you include dissipation.
Then we talk about open systems.
And for fundamental reasons, we need a formulation
using the density matrix, a statistical operator,
and a master equation.
One major part of the course is discussion and index derivation
of the mechanical forces of light.

This will include a discussion of
important experimental techniques using
those mechanical forces.
So various simple and sophisticated methods
of trapping and cooling.
We will spend some time in not talking about atoms at all.
We just want to talk about photons, about similar photons.
We want to understand where the photon nature of light
makes light very, very different and form
a classic electromagnetic wave.
Also, it's not the focus.
Cause We will come across basic building blocks
of quantum information science.
Pretty much when atom and photons interacts.
This is fundamental [INAUDIBLE].
And we'll talk about the many-body physics
of quantum gases.
So maybe it becomes clearer what we
are covering by seeing what we are not covering.
And this tells you that there is at least
some selection of topics.
It's not that we talk about everything.
We will not talk about the physics above 10 electron volt.
We will not talk about collisions.
Or maybe I should say high-energy collisions.

We will, of course, talk about [INAUDIBLE] collisions, which
is the physics of the scattering lengths
and some s-wave collisions, which are really
relevant to understand quantum gases.
We are not talking about any advanced topic
in atomic structure.
All we do about atom structure is done in 8.421.
And if you want to graduate in atomic physics at MIT,
yes, you have to understand atomic structure
at the level of the hydrogen atom
and maybe know a little bit what a new phenomena,
when another electron enters, when two electrons interact.
And that's the helium atom, but we are not going beyond it.
Let me just mention here that there
is, of course, more interesting things in atomic structure.
For instance, if you go to highly charged ions,
you have QED effects.
You can discuss very interesting correlations between two
electrons in an atom.
And you can have very relativistic effects
if you have highly ionized atoms.

If you have bare uranium, then the electron in the lowest
orbit becomes relativistic.
You can even see bare if you scale
the fine-structure constant, which
is an e-square in it with a charge of uranium, 92.
Well, 1 over 137 times 92 gives about 1.
So you really get into a new regime
of coupling for atomic physics.
And this may be an omission, because there's
really interesting work going on.
We're not talking about high-intensity lasers
and short laser pulses.
This choice may be mainly determined by that.
The experimental program in the physics department
is not overlapping with that.
But of course, we have world-class researchers
on short-pulse lasers in the electrical engineering
department.