Capacity of a lossy photon channel with direct detection

TL;DR

This paper numerically analyzes the capacity of a lossy photon channel with direct detection, comparing Fock and coherent states, and finds Fock states outperform coherent states under certain conditions.

Contribution

It provides a numerical evaluation of channel capacity for Fock and coherent states, highlighting the advantages of Fock states with direct detection in specific regimes.

Findings

Fock states outperform coherent states in capacity with direct detection.

Capacity approaches that of a discrete-time Poisson channel with Fock states.

Fock states are beneficial in moderate photon number and low loss regimes.

Abstract

We calculate numerically the capacity of a lossy photon channel assuming photon number resolving detection at the output. We consider scenarios of input Fock and coherent states ensembles and show that the latter always exhibits worse performance than the former. We obtain capacity of a discrete-time Poisson channel as a limiting behavior of the Fock states ensemble capacity. We show also that in the regime of a moderate number of photons and low losses the Fock states ensemble with direct detection is beneficial with respect to capacity limits achievable with quadrature detection.