English (United Kingdom)

https://curated-unify.zendy.io/wp-json/zendy-region/v1/featured_content/oa?rat=en

https://curated-unify.zendy.io/wp-json/zendy-region/v1/highlighted_journal/

Global: Zendy Plus annual

Presents the access of premium content as premium feature

Premium Content

Presents the keyphrase highlighting as premium feature

Keyphrase Highlighting

Presents the summarisation as premium feature

Summarisation

Insights

Presents the pdf analysis as premium feature

PDF Analysis

Presents the zaia usage as premium feature

ZAIA

Global: Zendy Tools annual

Global: Zendy Free Plan

Global: Zendy Tools monthly

Global: Zendy Plus monthly

Mixed states are introduced in physics in order to express our ignoranceabout the actual state of a physical system and are represented in standardquantum mechanics (QM) by density operators. Such operators also appear if oneconsiders a (pure) entangled state of a compound system $\Omega$ and performspartial traces on the projection operator representing it. Yet, they do notrepresent mixed states (or proper mixtures) of the subsystems in this case, butimproper mixtures, since the coefficients in the convex sums expressing themnever bear the ignorance interpretation. Hence, one cannot attribute states tothe subsystems of a compound physical system in QM (subentity problem). Wediscuss here two alternative proposals that can be worked out within theBrussels and Lecce approaches. We firstly summarize the general frameworkprovided by the former, which suggests that improper mixtures could beconsidered as new pure states. Then, we show that improper mixtures can beconsidered as true (yet nonpure) states also according to the latter. The twoproposals seem to be compatible notwithstanding their different terminologies.Comment: Revised Introduction. Minor changes in the abstract and in Secs. 2-

The physical interpretation of partial traces: Two nonstandard views