  We discuss the impact of gain and loss on the evolution of photonic quantum
states and find that PT-symmetric quantum optics in gain/loss systems is not
possible. Within the framework of macroscopic quantum electrodynamics we show
that gain and loss are associated with non-compact and compact operator
transformations, respectively. This implies a fundamentally different way in
which quantum correlations between a quantum system and a reservoir are built
up and destroyed.
