quantumfluid

Quantumfluid is a term used to describe a fluid in which quantum mechanical effects dominate its macroscopic behavior. In such systems, the de Broglie wavelengths of constituent particles are comparable to interparticle spacing, allowing collective quantum states to emerge. Quantumfluids include both bosonic systems, which can form a Bose-Einstein condensate, and fermionic systems, where pairing creates a coherent superfluid phase.

Common features include frictionless flow (superfluidity) at sufficiently low temperatures, quantized vortices with discrete circulation, and the existence of two components often described by the two-fluid model: a superfluid part and a normal part. Other signatures are long-range phase coherence, the appearance of second sound, and characteristic length scales such as healing length.

The theoretical description typically employs the Gross-Pitaevskii equation for weakly interacting Bose fluids, or quantum hydrodynamics derived from the Madelung transformation. More generally, many-body quantum theories, including Landau's two-fluid theory for helium and Fermi liquid theories for degenerate gases, are used to treat quantumfluids.

Experimental realizations span liquid helium-4 and helium-3 at cryogenic temperatures, ultracold atomic gases in magneto-optical traps forming Bose-Einstein condensates or paired superfluids, and exciton-polariton condensates in semiconductor microcavities. Quantumfluids are also studied in driven-dissipative setups and in superconducting circuits where Cooper pairs form a macroscopic quantum fluid.

The term quantumfluid is not always standard; many sources refer to quantum fluids or quantum hydrodynamics. In some contexts, quantumfluid is used as a generic label for fluids dominated by quantum coherence, without implying a specific microscopic mechanism.