Genuine certification of incompatible quantum instruments through sequential communication tasks

Quantum instruments constitute the general description of quantum dynamics, encompassing both quantum measurements and quantum channels as special cases. Consequently, the incompatibility of quantum instruments represents a fundamental manifestation of nonclassicality in quantum theory. Here, we establish the operational significance of this notion by demonstrating communication tasks with classical inputs and outputs that enable the semi-device-independent certification of incompatible quantum instruments. We introduce a class of three-party communication tasks involving a sender, a relayer, and a receiver, and derive the tight upper bound of the figure of merits of these tasks achievable by all compatible instruments implemented by the relayer and this bound coincides with the optimal performance attainable in a classical communication subject to the same dimensional constraints. Violation of this bound certifies the incompatibility of the pair of quantum instruments implemented by the relayer. This identifies certification of incompatible instruments as a manifestation of quantum advantage in communication. This certification protocol is genuine as it is able to certify the incompatibility of a pair of instruments where the measurements and channels induced by the instruments are pairwise compatible and, therefore it does not depend on the incompability of measurements and channels induced by the instruments. Finally, we identify the simplest instances of our communication scenario that enable the certification of incompatible quantum instruments.

Source: arXiv:2606.23647v1 - http://arxiv.org/abs/2606.23647v1 PDF: https://arxiv.org/pdf/2606.23647v1 Original Link: http://arxiv.org/abs/2606.23647v1