  While traditionally regarded as an obstacle to quantum coherence, recent
breakthroughs in quantum optics have shown that the dissipative interaction of
a qubit with its environment can be leveraged to protect quantum states and
synthesize many-body entanglement. Inspired by this progress, here we set the
stage for the -- yet uncharted -- exploration of analogous cooperative
phenomena in hybrid solid-state platforms. We develop a comprehensive formalism
for the quantum many-body dynamics of an ensemble of solid-state spin defects
interacting dissipatively with the magnetic field fluctuations of a common
solid-state reservoir. Our framework applies to any solid-state reservoir whose
fluctuating spin, pseudospin, or charge degrees of freedom generate magnetic
fields. To understand whether correlations induced by dissipative processes can
play a relevant role in a realistic experimental setup, we apply our model to a
qubit array interacting via the spin fluctuations of a ferromagnetic bath. Our
results show that the low-temperature collective relaxation rates of the qubit
ensemble can display clear signatures of super- and subradiance, i.e., forms of
cooperative dynamics traditionally achieved in atomic ensembles. We find that
the solid-state analog of these cooperative phenomena is robust against spatial
disorder in the qubit ensemble and thermal fluctuations of the magnetic
reservoir, providing a route for their feasibility in near-term experiments.
Our work lays the foundation for a multi-qubit approach to quantum sensing of
solid-state systems and the direct generation of many-body entanglement in
spin-defect ensembles. Furthermore, we discuss how the tunability of
solid-state reservoirs opens up novel pathways for exploring cooperative
phenomena in regimes beyond the reach of conventional quantum optics setups.
