# Inspection of the Density Matrix

1. Mar 31, 2010

### Lamont1986

I have a question about density matrices. Is there a way to deduce the purity of the density matrix just by inspection?

-L

2. Mar 31, 2010

### strangerep

I don't think you can deduce it just by inspection. One needs to at least
calculate $\rho^2$ and check that it has unit trace.
Cf. Ballentine pp 51-52.