How to describe collective decay of uncoupled modes in the input–output formalism

We extend the input–output formalism to study behavior of uncoupled discrete modes (bosonic cavity and fermionic qubits) when they decay same Markovian continuum. When continuum interacts with only a single mode, this is irreversible. However, multiple develop correlations collectively. In these manifest in additional terms quantum Langevin equation. For two modes, collective can dramatically lifetimes both (Dicke subradiance) and, within single-mode subsystem, induces non-Markovian memory effects including energy backflow.