Untangling Entanglement

In this paper recent work that attempts to link quantum entanglement to (i) thermodynamic energy, (ii) thermodynamic entropy and (iii) information is reviewed. With respect to the first two links the paper is essentially expository. The final link is elaborated on: it is argued that the value of the entanglement of a bipartite system in a pure state is equal to the value of the irreducible uncertainty (i.e. irreducibly missing information) about its subsystems and that this suggests that entanglement gives rise to irreducible uncertainty. (The exact meaning of the phrase “irreducible uncertainty”, as used here, is explained in the body of the paper. Roughly speaking, it is the uncertainty about the post-measurement state of a system that cannot be removed at the pre-measurement stage.) This analysis is used to make a further connection between entanglement and statistical mechanical entropy: it is argued that these properties are indirectly linked, in so far as both give rise to forms of uncertainty (albeit rather different forms of uncertainty about rather different things).