Stability of normal quantum-fluid mixtures

Mixtures of quantum fluids, that is gases or liquids, are considered with the emphasis on the conditions characterizing the stability of the mixtures. The mixtures, that can be formed by cold atoms or molecules, are assumed to be quantum requiring the description using quantum techniques, but not so cold that to exhibit superfluidity or superconductivity. Reviewing the stability conditions of such normal quantum systems is important for the comparison of these conditions with the stability conditions of, e.g., Bose-condensed mixtures. The behavior of observable quantities under the stratification of quantum mixtures is discussed.