In this Chapter, we give a brief review of the state of the art of theoretical and experimental studies of quantum fluids of light. Such systems consist of ensembles of photons that acquire a finite mass from spatial confinement or diffraction and finite binary interactions from the optical nonlinearity of the optical medium. The peculiar properties of these fluids are highlighted in comparison with standard condensed matter systems, with a special emphasis on the novel possibilities that they offer for the generation, the manipulation and the diagnostics of the fluid, as well as on their intrinsically non-equilibrium and/or dynamical nature. Perspectives towards a new generation of experiments on strongly correlated fluids of light and towards opto-electronic applications are finally sketched.
In a Fermi gas with a Fashbach resonance, one can tune the strengthof the paring interaction by adjusting the threshold energy of Feshbachresonance. The super-fluid density s is always equal to the total carrierdensity at T 0 which it vanishes at the super-fluid phase transition c T .These properties are satisfied in both Fermi and Bose super-fluid. There is acrucial difference between s in a Fermi superfluid and that in a Bose superfluid.In a mean field BCS theory originates from the thermal dissociationof cooper pairs.There it was observed that that if one increases the strength of thepairing interaction BCS type normal fluid density dominated by quasi-particleexcitation change into BES type normal fluid density dominated byBogoliubov collective excitations. As super-fluid density s plays animportant role in two fluid hydrodynamics these evaluated results would beuseful in the study of dynamical properties in the BCS-BEC crossover regionat finite temperature.