We investigate a counter-intuitive phenomenon of quantum state discrimination that the success probability of
identifying all the unknown quantum states increases even when the number of unknown states increases. The
phenomenon is known for vulnerability of quantum secret sharing (QSS), which enables one to distribute a secret
amongst untrusted participants securely, however, the necessary and sufficient condition for the phenomenon
was unknown. We show the condition for a specific discrimination task and construct a practical method to realize
the phenomenon. These results advance the analysis of the phenomenon and reveal the vulnerability of QSS.
Since quantum state discrimination lies at the heart of many quantum information processing tasks, our research
widely contributes to the future information society based on quantum technologies, where people would obtain
the benefits from genuine quantum information processing.
Seiseki Akiube, Theory Research Group, Media Information Laboratory