Abstract

Quantum Shannon theory aims to understand the information processing capabilities of quantum systems in the form of capacities. Unlike in Shannon’s classical theory, we now know that many of these are not additive, making the landscape of phenomena in the quantum case much richer; also, it seems to make it much more difficult to evaluate these quantum capacities. The same goes for entanglement measures. After the dramatic progress of Hastings, Smith and Yard, and others, from a couple of years ago, I will here report on the entanglement of purification (EoP) [Terhal et al., JMP 43 :4286 (2002)], which measures the total amount of correlation needed to prepare a state. In joint work with Jianxin Chen (IQC Waterloo) we show strong evidence that EoP is not additive, although it is known to be additive for certain families of states.