Linear optics and photodetection achieve near-optimal unambiguous coherent state discrimination

Understand

Coherent states of the quantum electromagnetic field, the quantum description of ideal laser light, are prime candidates as information carriers for optical communications.

• A large body of literature exists on their quantum-limited estimation and discrimination.
• However, very little is known about the practical realizations of receivers for unambiguous state discrimination (USD) of coherent states.
• Here we fill this gap and outline a theory of USD with receivers that are allowed to employ: passive multimode linear optics, phase-space displacements, auxiliary vacuum modes, and on-off photon detection.