Capacities of linear quantum optical systems

TL;DR

This paper models diffraction in optical communication channels as a memory channel and demonstrates that an optical refocusing system can significantly enhance classical communication capacity despite inherent losses.

Contribution

It introduces a formal description of diffraction as a memory channel and analyzes how a converging lens can improve communication capacity in optical systems.

Findings

Diffraction can be modeled as a memory channel.

Refocusing systems can substantially increase communication capacity.

Losses due to finite pupils can be mitigated by optical refocusing.

Abstract

A wide variety of communication channels employ the quantized electromagnetic field to convey information. Their communication capacity crucially depends on losses associated to spatial characteristics of the channel such as diffraction and antenna design. Here we focus on the communication via a finite pupil, showing that diffraction is formally described as a memory channel. By exploiting this equivalence we then compute the communication capacity of an optical refocusing system, modeled as a converging lens. Even though loss of information originates from the finite pupil of the lens, we show that the presence of the refocusing system can substantially enhance the communication capacity. We mainly concentrate on communication of classical information, the extension to quantum information being straightforward.