Demonstration of 𝒫𝒯 -symmetric quantum state discrimination

The fundamental quantum mechanical features forbid non-orthogonal quantum states to be distinguished accurately through a single-shot measurement. Using parity-time ( 𝒫𝒯 ) quantum mechanics, however, a perfect state discrimination with certainty can be implemented. Here, we experimentally implement quantum state discrimination for photonic single-qubit states by executing post-selected gates and loss-based non-unitary evolutions in the 𝒫𝒯 -symmetric system, providing a relatively superior strategy for state discrimination in non-Hermitian systems. We also unveil the origin of 𝒫𝒯 quantum state discrimination by embedding the 𝒫𝒯 dynamics into a higher-level system under unitary dynamics. This experimental work demonstrates the key principle of 𝒫𝒯 quantum state discrimination and opens a door of other effective approaches in the 𝒫𝒯 -symmetric quantum mechanics.