Eur. Phys. J. B 86 (2013) 86: 328
https://doi.org/10.1140/epjb/e2013-40424-5

Regular Article

Physics behind the minimum of relative entropy measures for correlations

¹ Institute of Solid State Physics, Vienna University of Technology, 1040 Vienna, Austria
² Wolfgang Pauli Inst. c/o Fak. Mathematik, Univ. Wien, 1090 Vienna, Austria

^a e-mail: held@ifp.tuwien.ac.at

Received: 22 April 2013
Received in final form: 4 June 2013
Published online: 22 July 2013

Abstract

The relative entropy of a correlated state and an uncorrelated reference state is a reasonable measure for the degree of correlations. A key question is, however, which uncorrelated state to compare to. The relative entropy becomes minimal for the uncorrelated reference state that has the same one-particle density matrix as the correlated state. Hence, this particular measure, coined nonfreeness, is unique and reasonable. We demonstrate that for relevant physical situations, such as finite temperatures or a correlation enhanced orbital splitting, other choices of the uncorrelated state, even educated guesses, overestimate correlations.