zerotemperature

Zerotemperature (also written zero-temperature) describes the limit in which a physical system's temperature tends toward absolute zero, 0 kelvin. In this regime, thermal fluctuations are greatly reduced and the behavior of matter is governed primarily by quantum mechanics rather than classical thermodynamics.

Temperature is a measure of average kinetic energy of microscopic constituents. As T approaches 0 K, the classical notion of particles ceasing movement is replaced by the concept of a ground state with minimal energy; quantum zero-point motion persists. According to the third law of thermodynamics, the entropy of a perfect crystalline system tends to zero as temperature tends to zero, though some systems retain residual entropy due to degeneracy.

Experimentally, temperatures close to zerotemperature are achieved using laser cooling, evaporative cooling, and sympathetic cooling in ultracold atomic gases. For condensed matter and cryogenic devices, dilution refrigeration can reach millikelvin and microkelvin regimes. At zerotemperature, many systems exhibit quantum phenomena such as Bose–Einstein condensation, superconductivity, and superfluidity. The zerotemperature limit is also a common theoretical reference in quantum many-body physics, where systems are analyzed in their ground states and low-energy excitations.

Although absolute zero cannot be reached by any finite sequence of operations (the Nernst unattainability principle), modern experiments reach ultracold regimes in the nanokelvin to microkelvin range, enabling the study of ground-state properties and quantum phase transitions that are inaccessible at higher temperatures. Zerotemperature thus serves as a foundational idealization for understanding quantum phenomena in condensed matter and atomic physics.