An approximate unique extension property for completely positive maps

Abstract

We study the closure of the unitary orbit of a given point in the non-commutative Choquet boundary of a unital operator space with respect to the topology of pointwise norm convergence. This may be described more extensively as the ⁎-representations of the C⁎-envelope that are approximately unitarily equivalent to one that possesses the unique extension property. Although these ⁎-representations do not necessarily have the unique extension property themselves, we show that their unital completely positive extensions display significant restrictions. When the underlying operator space is separable, this allows us to connect our work to Arveson's hyperrigidity conjecture. Finally, as an application, we reformulate the classical Šaškin Theorem and Arveson's essential normality conjecture.