A simple proof of the strong subadditivity inequality
arXiv:quant-ph/0408130
Abstract
Arguably the deepest fact known about the von Neumann entropy, the strong subadditivity inequality is a potent hammer in the quantum information theorist's toolkit. This short tutorial describes a simple proof of strong subadditivity due to Petz [Rep. on Math. Phys. 23 (1), 57--65 (1986)]. It assumes only knowledge of elementary linear algebra and quantum mechanics.
7 pages, resubmitted version of a tutorial paper submitted to Quantum Information and Computation