Del Rio L Hutter A Renner R Wehner S 2016 Locally thermal quantum systems may contradict traditional thermodynamics: heat can flow from a cold body to a hotter one, if the two are highly entangled. We show that to recover thermodynamic laws, we must use a stronger notion of thermalization: a system S is thermal relative to a reference R if S is both locally thermal and uncorrelated with R. Considering a general quantum reference is particularly relevant for a thermodynamic treatment of nanoscale quantum systems. We derive a technical condition for relative thermalization in terms of conditional entropies. Established results on local thermalization, which implicitly assume a classical reference, follow as special cases. application/pdf https://sonar.ch/global/documents/199634 eng info:eu-repo/semantics/altIdentifier/doi/10.1103/PhysRevE.94.022104 info:eu-repo/semantics/altIdentifier/pmid/27627243 info:eu-repo/semantics/openAccess Physical review. E. - 2016 Relative thermalization. http://purl.org/coar/resource_type/c_6501