  A minimal energy quantum superposition of two maximally distinguishable,
isoenergetic single mode Gaussian states is used to construct the
system-environment representation of a class of linear bosonic quantum channels
acting on a single bosonic mode. The quantum channels are further defined by
unitary dynamics of the system and environment corresponding to either a
passive linear optical element $U_{\text{BS}}$ or two-mode squeezing
$U_{\text{TM}}$. The notion of nonclassicality distance is used to show that
the initial environment superposition state becomes maximally nonclassical as
the constraint energy is increased. When the system is initially prepared in a
coherent state, application of the quantum channel defined by $U_{\text{BS}}$
results in a nonclassical state for all values of the environment energy
constraint. We also discuss the following properties of the quantum channels:
1) the maximal noise that a coherent system can tolerate, beyond which the
linear bosonic attenuator channel defined by $U_{\text{BS}}$ cannot impart
nonclassical correlations to the system, 2) the noise added to a coherent
system by the phase-preserving linear amplification channel defined by
$U_{\text{TM}}$, and 3) a generic lower bound for the trace norm contraction
coefficient on the closed, convex hull of energy-constrained Gaussian states.
