  Based on the system-reservoir description we propose a simple solvable
microscopic model for a nonequilibrium bath. This captures the essential
features of a nonstationary quantum Markov process. We establish an appropriate
generalization of the fluctuation-dissipation relation pertaining to this
process and explore the essential modifications of the Bloch equations to
reveal the nonexponential decay of the Bloch vector components and transient
spectral broadening in resonance fluorescence. We discuss a simple experimental
scheme to verify the theoretical results.
