![]() ![]() ![]() Recently, it has been realized that under suitable circumstances photons can acquire an effective mass and will behave as a quantum fluid of light with photon-photon interactions. However, we know since the early days of quantum mechanics, that photons in a box can be interpreted as a massless Bose gas of non-interacting particules. This fruitful interpretation leads for example to the correct black-body radiation spectrum. Historically, this area of research (theoretical and experimental) deals with massive material particules (atoms, electrons…). ![]() When interactions between particules are not negligible, physics become even more fascinating with purely quantum effects fading in, like superconductivity, superfluidity and the fractional quantum Hall effect. Surprisingly, these very different systems show similar behavior when the thermal de Broglie wavelength becomes comparable or larger than the average inter-particle spacing. In this regime, the Bose versus Fermi statistics of the particules starts playing a critical role in determining the properties of the fluid. For exemple, non-interacting fermions will exhibit Fermi pressure down to zero temperature thanks to the rigidity of the Fermi sphere, while in a non-interacting Bose gas a macroscopic fraction of the particules will ac- cumulates in the lowest-energy state, leading to a Bose-Einstein condensate. A large range of many-particle systems are currently under intense investigation, from liquid Helium to electrons in solids, to quark-gluon plasma and trapped gases of ultra-cold atoms. Quantum fluids Physics is the study of hydrodynamic systems which demonstrate a quantum behavior. ![]()
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