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M5intro.txt
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M5intro.txt
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#
# File: content-mit-8-421-5x-subtitles/M5intro.txt
#
# Captions for 8.421x module
#
# This file has 34 caption lines.
#
# Do not add or delete any lines.
#
#----------------------------------------
Welcome to module five of the course
on atomic and optical physics.
We finish this sequence with the topic of coherence.
Coherence has always fascinated me,
because it is at the heart of many important phenomena
in physics.
Coherence leads to beautiful interference of visible light,
and coherence is also the mechanism behind superphenomena
like superfluidity, superconductivity,
and superradiance.
Coherence occurs when we have a definite phase
between two or more amplitudes, which can then interfere.
This general principle can be found in many phenomena
in atomic and optical physics.
We start out by discussing superposition between two
quantum states within one atom, and then
we generalize it to three levels.
The step from two to three levels
allows us to discuss many interesting and
counterintuitive phenomena, like electromagnetically
induced transparency, lasing without inversion, and stopped
and slow light.
We then discuss coherence between atoms.
To give you an example, when you have two atoms,
and one atoms is in an excited state,
it may not be able to emit a photon
because there is destructive interference between the two
atoms.
We can generalize this to many atoms,
and then we have the phenomenon of superradiance.
A chromatic phenomenon which occurs
when many atoms collectively interact with the radiation
field.