22.51 Quantum Theory of Radiation Interactions

Notation

Mathjax notation from Tutorial: How to use TeX/MathJax to render math notation? - Quantum Computing Meta Stack Exchange

Let’s parse this. I was originally going to note that \langle A,B\rangle is “the commutation” but it totally isn’t.

The trace of a matrix is the sum of the diagonal elements. The trace of a vector

\newcommand{\bra}[1]{\left<#1\right|}\newcommand{\ket}[1]{\left|#1\right>}\newcommand{\bk}[2]{\left<#1\middle|#2\right>}\newcommand{\bke}[3]{\left<#1\middle|#2\middle|#3\right>}

2010 midterm question 1