  Quantum ensembles form easily accessible architectures for studying various
phenomena in quantum physics, quantum information science, and spectroscopy.
Here we review some recent protocols for measurements in quantum ensembles by
utilizing ancillary systems. We also illustrate these protocols experimentally
via nuclear magnetic resonance techniques. In particular, we shall review
noninvasive measurements, extracting expectation values of various operators,
characterizations of quantum states, and quantum processes, and finally quantum
noise engineering.
