Ch 11.1 The mathematical construction for combining two quantum systems: $\mathcal{H}_{AB} = \mathcal{H}_A \otimes \mathcal{H}_B$. If $\dim(\mathcal{H}_A) = n$ and $\dim(\mathcal{H}_B) = m$, then $\dim(\mathcal{H}_{AB}) = nm$. Product states have the form $|\psi_A\rangle \otimes |\phi_B\rangle$; ent