  We consider non-interacting multi-qubit systems as controllable probes of an
environment of defects/impurities modelled as a composite spin-boson
environment. The spin-boson environment consists of a small number of
quantum-coherent two-level fluctuators (TLFs) damped by independent bosonic
baths. A master equation of the Lindblad form is derived for the probe-plus-TLF
system. We discuss how correlation measurements in the probe system encode
information about the environment structure and could be exploited to
efficiently discriminate between different experimental preparation techniques,
with particular focus on the quantum correlations (entanglement) that build up
in the probe as a result of the TLF-mediated interaction. We also investigate
the harmful effects of the composite spin-boson environment on initially
prepared entangled bipartite qubit states of the probe and on entangling gate
operations. Our results offer insights in the area of quantum computation using
superconducting devices, where defects/impurities are believed to be a major
source of decoherence.
