Self-testing of semisymmetric informationally complete measurements in a qubit prepare-and-measure scenario

Self-testing is a powerful method for certifying quantum systems. Initially proposed in the device-independent (DI) setting, self-testing has since been relaxed to the semi-device-independent (semi-DI) setting. In this study, we focus on the self-testing of a specific type of nonprojective qubit measurements belonging to a one-parameter family, using the semi-DI prepare-and-measure (PM) scenario. Remarkably, we identify the simplest PM scenario discovered so far, involving only four preparations and four measurements, for self-testing the fourth measurement. This particular measurement is a four-outcome nonprojective positive operator-valued measure (POVM) and falls in the class of semisymmetric informationally complete POVMs introduced by Geng et al. [Phys. Rev. Lett. 126, 100401 (2021)]. To achieve this, we develop analytic techniques for semi-DI self-testing in the PM scenario. Our results pave the way toward self-testing any extremal qubit POVM within a potentially minimal PM scenario.