- #1

Josh Conneely

- 1

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## Homework Statement

Suppose a 2x2 matrix X (not necessarily hermitian, nor unitary) is written as

X = a0 +

**sigma . a**(the sigma . a is a dot product between sigma and a)

where a0 and a1, a2 and a3 are numbers.

How on Earth does X represent a matrix? it's a number added to another number (dot product).