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 Tools annual

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 monthly

Global: Zendy Plus monthly

Presents the access of premium content as premium feature

Premium Content

Global: Zendy Plus annual

Global: Zendy Free Plan

A bosonic state is commonly considered nonclassical (or quantum) if itsGlauber-Sudarshan $P$ function is not a classical probability density, whichimplies that only coherent states and their statistical mixtures are classical.We quantify the nonclassicality of a single qubit, defined by the vacuum andsingle-photon states, by applying the following four well-known measures ofnonclassicality: (1) the nonclassical depth, $\tau$, related to the minimalamount of Gaussian noise which changes a nonpositive $P$ function into apositive one; (2) the nonclassical distance $D$, defined as the Bures distanceof a given state to the closest classical state, which is the vacuum for thesingle-qubit Hilbert space; together with (3) the negativity potential (NP) and(4) concurrence potential, which are the nonclassicality measures correspondingto the entanglement measures (i.e., the negativity and concurrence,respectively) for the state generated by mixing a single-qubit state with thevacuum on a balanced beam splitter. We show that complete statistical mixturesof the vacuum and single-photon states are the most nonclassical single-qubitstates regarding the distance $D$ for a fixed value of both the depth $\tau$and NP in the whole range $[0,1]$ of their values, as well as the NP for agiven value of $\tau$ such that $\tau>0.3154$. Conversely, pure states are themost nonclassical single-qubit states with respect to $\tau$ for a given $D$,NP versus $D$, and $\tau$ versus NP. We also show the "relativity" of thesenonclassicality measures by comparing pairs of single-qubit states: if a stateis less nonclassical than another state according to some measure then it mightbe more nonclassical according to another measure. Moreover, we find that theconcurrence potential is equal to the nonclassical distance for single-qubitstates.

Statistical mixtures of states can be more quantum than their superpositions: Comparison of nonclassicality measures for single-qubit states