Four-state discrimination via a homodyne-Kennedy hybrid receiver

Quantum communication allows for deep space communication and secure transmission of information. The perfomance and security of such protocols is based on the non-orthogonality of the used states, which is a key feature of quantum mechanics. The task of a quantum receiver is to discriminate between different states in a given alphabet with minimum error. This gives rise to the necessity of having receivers with a minimum amount of discrimination errors approaching the limits imposed by quantum mechanics [1,2]. Conventional detection schemes fail to fulfill this task, which makes the study of quantum receivers an important field in the realm of quantum communication.