Quantum Correlations on Quantum Spaces
Piotr Mikołaj Sołtan, Paweł Kasprzak, Arkadiusz Bochniak
Abstract
Abstract For given quantum (non-commutative) spaces ${\mathbb {P}}$ and ${\mathbb {O}}$, we study the quantum space of maps ${\mathbb {M}}_{{\mathbb {P}},{\mathbb {O}}}$ from ${\mathbb {P}}$ to ${\mathbb {O}}$. In case of finite quantum spaces, these objects turn out to be behind a large class of maps which generalize the classical $\textrm {qc}$-correlations known from quantum information theory to the setting of quantum input and output sets. We prove various operator algebraic properties of the ${\textrm C}^\ast$-algebras ${\operatorname {C}}({\mathbb {M}}_{{\mathbb {P}},{\mathbb {O}}})$ such as the lifting property and residual finite dimensionality. Inside ${\operatorname {C}}({\mathbb {M}}_{{\mathbb {P}},{\mathbb {O}}})$ we construct a universal operator system ${\mathbb {S}}_{{\mathbb {P}},{\mathbb {O}}}$ related to ${\mathbb {P}}$ and ${\mathbb {O}}$, and show, among other things, that the embedding ${\mathbb {S}}_{{\mathbb {P}},{\mathbb {O}}}\subset {\operatorname {C}}({\mathbb {M}}_{{\mathbb {P}},{\mathbb {O}}})$ is hyperrigid and has another interesting property, which we call the strong extension property. Furthermore, ${\operatorname {C}}({\mathbb {M}}_{{\mathbb {P}},{\mathbb {O}}})$ is the ${\textrm C}^\ast$-envelope of ${\mathbb {S}}_{{\mathbb {P}},{\mathbb {O}}}$ and a large class of non-signalling correlations on the quantum sets ${\mathbb {P}}$ and ${\mathbb {O}}$ arise from states on ${\operatorname {C}}({\mathbb {M}}_{{\mathbb {P}},{\mathbb {O}}})\otimes _{\text {\tiny {\textrm {max}}}}{\operatorname {C}}({\mathbb {M}}_{{\mathbb {P}},{\mathbb {O}}})$ as well as states on the commuting tensor product ${\mathbb {S}}_{{\mathbb {P}},{\mathbb {O}}}\otimes _{\text {\tiny {\textrm {c}}}}{\mathbb {S}}_{{\mathbb {P}},{\mathbb {O}}}$. Finally, we introduce and study the notion of a synchronous correlation with quantum input and output sets and prove several characterizations of such correlations and their relation to traces on ${\operatorname {C}}({\mathbb {M}}_{{\mathbb {P}},{\mathbb {O}}})$.