  We introduce a class of quantum channels called passive-environment bosonic
channels. These channels are relevant from a quantum thermodynamical viewpoint
because they correspond to the energy-preserving linear coupling of a bosonic
system with a bosonic environment that is in a passive state (no energy can be
extracted from it by using a unitary transformation) followed by discarding the
environment. The Fock-majorization relation defined in [New J. Phys. 18, 073047
(2016)] happens to be especially useful in this context as, unlike regular
majorization, it connects the disorder of a state together with its energy. Our
main result here is the preservation of Fock majorization across all
passive-environment bosonic channels. This implies a similar preservation
property for regular majorization over the set of passive states, and it also
extends to passive-environment channels whose Stinespring dilation involves an
active Gaussian unitary. Beyond bosonic systems, the introduced class of
passive environment operations naturally generalizes thermal operations and is
expected to provide new insights into the thermodynamics of quantum systems.
