title: Uniform Additivity in Classical and Quantum Information.
abstract: Information theory quantifies the optimal rates of resource interconversions, usually in terms of entropies. However, nonadditivity often makes evaluating entropic formulas intractable. In a few auspicious cases, additivity allows a full characterization of optimal rates. We study uniform additivity of formulas, which is easily evaluated and captures all known additive quantum formulas. Our complete characterization of uniform additivity exposes an intriguing new additive quantity and identifies a remarkable coincidence-the classical and quantum uniformly additive functions with one auxiliary variable are identical.
authors.affiliation: IBM TJ Watson Research Center, Yorktown Heights, New York 10598, USA.
authors.forename: Andrew
authors.initials: A
authors.lastname: Cross
authors.affiliation: IBM TJ Watson Research Center, Yorktown Heights, New York 10598, USA.|Center for Theoretical Physics, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA.|IQIM, California Institute of Technology, Pasadena, California 91125, USA.
authors.forename: Ke
authors.initials: K
authors.lastname: Li
authors.affiliation: JILA and Department of Physics, University of Colorado, Boulder, Colorado 80309, USA.
authors.forename: Graeme
authors.initials: G
authors.lastname: Smith