Środowiskowe Seminarium z Informacji i Technologii Kwantowych

For reliable optical communication state discrimination is a critical task. Quantum measurements can provide significant enhancement in information transfer compared to classical techniques and enable detection below the shot-noise limit. Noise in the communication channel or the measurement, however, limits the benefits of quantum-enhanced techniques. Whereas linear losses result in a simple rescaling of the complex field amplitude, the effects of phase diffusion are less trivial. Phase noise can arise as linear noise or nonlinear phase noise caused by nonlinear interactions. Already when communicating via a lossy Kerr medium nonlinear phase noise arises fundamentally and limits the information transfer.Here we consider a receiver based on a displacement operation followed by photon counting with finite photon number resolution. For binary alphabets of coherent states such a receiver provides a near optimal scaling of the error probability with the energy of the signal close to the Dolinar receiver, while having less stringent technical requirements. We analyze the performance of the displacement receiver compared to conventional measurements and present a novel strategy to mitigate the effects of phase noise, both linear and nonlinear.