Conclusive discrimination by $N$ sequential receivers between $r\geq2$ arbitrary quantum states

Abstract: In the present article, we develop a general framework for the description of discrimination between $r\geq2$ quantum states by $N\geq1$ sequential receivers in the case where each receiver obtains a conclusive result. This type of discrimination constitutes an $N$-sequential extension of the minimum-error discrimination by one receiver. The developed general framework, which is valid for a conclusive discrimination between any number $r\geq2$ of arbitrary quantum states, pure or mixed, of an arbitrary dimension and any number $N\geq1$ of sequential receivers, is based on the notion of a quantum state instrument and this allows us to derive the new important general results. We, in particular, find a general condition on $r\geq2$ quantum states, under which, within the strategy where all types of receivers' quantum measurements are allowed, the optimal success probability is equal to that of the first receiver for any number $N\geq2$ of further sequential receivers. Furthermore, we extend our general framework to include an $N$-sequential conclusive discrimination between $r\geq2$ arbitrary quantum states under a noisy communication. As an example, we analyze analytically and numerically a two-sequential conclusive discrimination between two qubit states via depolarizing quantum channels. The derived new general results are important both from the theoretical point of view and for the development of a successful multipartite quantum communication via noisy quantum channels.