  Dissipative solitons are non-decaying out-of-equilibrium entities that result
from double balances between gain and loss, as well as nonlinearity and
dispersion. Here we describe a scenario where double balances rely on the
presence of multiple collective excitation channels in open-dissipative quantum
systems. It differs from conventional single-channel scenario for well-known
dissipative solitons such as dissipative Kerr solitons, in that the soliton
itself arises in a decoupled excitation channel and hence coherent nonlinear
excitation dynamics, but its background state corresponds to other channels and
is determined by the balance of pumping and dissipation. We demonstrate with a
spinor polariton Bose-Einstein condensate (BEC) under spatially uniform
nonresonant pumping, and show the existence of a dissipative magnetic soliton
as an exact solution to two-component driven-dissipative Gross-Pitaevskii
equation. This magnetic polariton soliton manifests as a localized spin
polarization with the background state being linearly polarized, and does not
decay when propagating in the dissipative medium. Our present work offers a new
perspective as well as new benchmarks for understanding and realizing
dissipative solitons.
