English

Reflected entropy is not a correlation measure

High Energy Physics - Theory 2023-06-08 v2 Quantum Physics

Abstract

By explicit counterexample, we show that the "reflected entropy" defined by Dutta and Faulkner is not monotonically decreasing under partial trace, and so is not a measure of physical correlations. In fact, our counterexamples show that none of the R\'enyi reflected entropies SR(α)S_{R}^{(\alpha)} for 0<α<20 < \alpha < 2 is a correlation measure; the usual reflected entropy is realized as the α=1\alpha=1 member of this family. The counterexamples are given by quantum states that correspond to classical probability distributions, so reflected entropy fails to measure correlations even at the classical level.

Cite

@article{arxiv.2302.10208,
  title  = {Reflected entropy is not a correlation measure},
  author = {Patrick Hayden and Marius Lemm and Jonathan Sorce},
  journal= {arXiv preprint arXiv:2302.10208},
  year   = {2023}
}

Comments

v1 is 4 pages long; v2 contains light edits to bring the preprint in line with the published version, and is 4.5 pages long

R2 v1 2026-06-28T08:44:53.184Z