Macroscopic quantum phenomena

Condensation of fermions occurs in superconductivity, and superfluid 3He condensation of bosons is found in superfluid 4He and in the laser. These phenomena are described. Then it will be asked whether a coherent quantum state could occur in a quantum paraelectric such as SrTiO3. Electron paramagnetic resonance, recent high-energy X-ray diffraction and accurate elastic constant measurements in this double oxide would be compatible with the existence of such a state and will be reviewed. If such a coherent state exists, second sound perpendicular to the tetragonal c-axis in SrTiO3 could be observed.