%0 Journal Article
%T Eigenstate Thermalization and Representative States on Subsystems
%A Vedika Khemani
%A Anushya Chandran
%A Hyungwon Kim
%A S. L. Sondhi
%J Physics
%D 2014
%I arXiv
%R 10.1103/PhysRevE.90.052133
%X We consider a quantum system A U B made up of degrees of freedom that can be partitioned into spatially disjoint regions A and B. When the full system is in a pure state in which regions A and B are entangled, the quantum mechanics of region A described without reference to its complement is traditionally assumed to require a reduced density matrix on A. While this is certainly true as an exact matter, we argue that under many interesting circumstances expectation values of typical operators anywhere inside A can be computed from a suitable pure state on A alone, with a controlled error. We use insights from quantum statistical mechanics - specifically the eigenstate thermalization hypothesis (ETH) - to argue for the existence of such "representative states".
%U http://arxiv.org/abs/1406.4863v1