Generalized sequential state discrimination for multiparty QKD and its optical implementation

Scientific Reports. 2020. Vol. 10. No. 1. P. 8247-1–8247-35.

Min N., Kwon Y.

Sequential state discrimination is a strategy for N separated receivers. As sequential state
discrimination can be applied to multiparty quantum key distribution (QKD), it has become one of
the relevant research fields in quantum information theory. Up to now, the analysis of sequential
state discrimination has been confined to special cases. In this report, we consider a generalization of
sequential state discrimination. Here, we do not limit the prior probabilities and the number of quantum
states and receivers. We show that the generalized sequential state discrimination can be expressed
as an optimization problem. Moreover, we investigate a structure of generalized sequential state
discrimination for two quantum states and apply it to multiparty QKD. We demonstrate that when the
number of receivers is not too many, generalized sequential state discrimination for two pure states can
be suitable for multiparty QKD. In addition, we show that generalized sequential state discrimination
for two mixed states can be performed with high optimal success probability. This optimal success
probability is even higher than those of quantum reproducing and quantum broadcasting strategy.
Thus, generalized sequential state discrimination of mixed states is adequate for performing multiparty
QKD. Furthermore, we prove that generalized sequential state discrimination can be implemented
experimentally by using linear optics. Finally, we analyze the security of multiparty QKD provided
by optimal sequential state discrimination. Our analysis shows that the multiparty QKD guarantees
nonzero secret key rate even in low channel efficiency.

Keywords: quantum information theory, Квантовая теория информации