  Recently, the Gaussian optimizer conjecture in quantum information theory was
confirmed for bosonic Gaussian gauge-covariant or contravariant channels. These
results use the i.i.d. model of the quantum noise. In this paper we consider
quantum Gaussian signal+noise model with time-continuous stationary coloured
noise. A proof of the coding theorem for the classical capacity of quantum
broadband gauge-covariant Gaussian channels is given. We also discuss and
compare the "broadband" and the "bandpass" models of time-continuous
time-continuous stationary coloured noise.
