Quantum phase transition

The transition describes an abrupt change in the ground state of a many-body system due to its quantum fluctuations.

As a result, the topological charge of Fermi liquid changes abruptly, since it takes only one of a discrete set of values.

The classical phase transitions are driven by a competition between the energy of a system and the entropy of its thermal fluctuations.

A phase transition from water to ice, for example, involves latent heat (a discontinuity of the internal energy

Although the thermodynamic average of the order parameter is zero in the disordered state, its fluctuations can be nonzero and become long-ranged in the vicinity of the critical point, where their typical length scale ξ (correlation length) and typical fluctuation decay time scale τc (correlation time) diverge: where is defined as the relative deviation from the critical temperature Tc.

Instead, quantum fluctuations, arising from Heisenberg's uncertainty principle, drive the loss of order characteristic of a QPT.

Although absolute zero is not physically realizable, characteristics of the transition can be detected in the system's low-temperature behavior near the critical point.