Non-Markovian quantum feedback networks I: Quantum transmission lines, lossless bounded real property and limit Markovian channels

Abstract

The purpose of this paper is to set out the problems of modeling quantum communication and signal processing where the communication between systems is via a non-Markovian channel. This is a general feature of quantum transmission lines. Our ultimate objective is to extend the network rules that have been developed for Markovian models. To this end we recall the Hamiltonian description of such non-Markov models of transmission lines and their quantization. These have occurred in the context of non-equilibrium thermodynamics, but our interest is in the transmission lines as carriers of information rather than heat baths. We show that there is an analytic scattering matrix associated with these models and that stability may be formulated in terms of the lossless bounded real property. Noting that the input and output fields do not separately satisfy a non-self-demolition principle, we discuss the rigorous limit in which such models appear Markov and so amenable to standard approaches of quantum filtering and control.