  Non-classical correlations in quantum optics as resources for quantum
computation are important in the quest for highly-specialized quantum devices.
The standard way to investigate such effects relies on either the
characterization of the inherent features of sources and circuits or the study
of the output radiation of a given optical setup. The latter approach demands
an extensive description of the output fields, but often overlooks the dynamics
of the sources. Conversely, the former discards most of the information about
the single trajectories, which are observed in experimental measurements. In
this work we provide a natural link between the two frameworks by exploiting
the thermodynamics of quantum trajectories. This procedure enables
investigation of the quantum properties of the photon fields from a generic
source via the analysis of the fluctuations and correlations of time-integrated
quantities associated with the photon counting of the emitted light.
