The adiabatic approximation

The adiabatic approximation Motivation In time independent perturbation theory, we saw that a time dependent perturbation can cause transitions For this to occur, frequency of the perturbation…

Poynting's theorem

Poynting's Theorem If we have some charge and current configuration which, produces some fields and . After a while, the charges move around. The question is, how much work is done by the…

Maxwell's Stress Tensor

Maxwell's Stress Tensor The total electromagnetic force on the charges in volume is Then, the force per volume is Using the Maxwell equations, we can get rid of and using the Maxwell's…

The Origins of Quanta

Science before the Quantum age Imagine that you were a scientist living in the 1800s. Classical physics, was well understood by everyone. At the time, there are really three branches of physics…

Introduction to Second Quantization

A particle in a box The Infinite Potential Box It's commonly said that a Quantum Field is a bunch of Harmonic Oscillators. To see what's really going on, let's start with a particle in a box: Inside…

What is Shannon Information?

Information theory started with Claude Shannon's 1948 paper, where he was trying to solve the problem of how to communicate through electrical signals. Electrical signals have two letters. 1 or 0. The…

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Zhi Han