noncondensed

Noncondensed is an adjective used to denote a state, phase, or component that is not in a condensed form. In physics and related sciences, condensation refers to the transition where matter becomes a dense, tightly bound phase such as a liquid or a solid, or, in quantum fluids, a macroscopic occupation of a single quantum state. By contrast, noncondensed describes matter that remains in a disordered, gaseous, or dilute state, or refers to parts of a system that have not undergone condensation. The term is most common in discussions of phases and phase transitions where both condensed and noncondensed components are present.

In the context of ultracold quantum gases, noncondensed often appears in the description of Bose-Einstein condensates. At finite temperatures, a trapped Bose gas can split into a condensed part, forming a Bose-Einstein condensate, and a noncondensed part, known as the thermal or noncondensed fraction. This noncondensed fraction consists of particles occupying excited states above the ground state. Its size grows with temperature and decreases as the system approaches absolute zero, where the condensate dominates.

The noncondensed fraction is a key quantity for understanding the thermodynamics and dynamics of quantum gases. It influences density and momentum distributions, coherence properties, and collective excitations. Experimental techniques such as time-of-flight imaging and spectroscopic probes help distinguish the condensed and noncondensed components and quantify their populations.

Overall, noncondensed serves as a useful descriptor for parts of a system that have not undergone condensation, particularly in studies of phase transitions, quantum statistics, and many-body physics.