Editing Quantum phase transition (section)

{{Short description|Transition between different phases of matter at zero temperature}}
In [[physics]], a '''quantum phase transition''' ('''QPT''') is a [[phase transition]] between different [[quantum phases]] ([[Phase (matter)|phases of matter]] at [[absolute zero|zero temperature]]). Contrary to classical phase transitions, quantum phase transitions can only be accessed by varying a physical parameter—such as [[magnetic field]] or pressure—at [[absolute zero]] temperature. The transition describes an abrupt change in the [[ground state]] of a many-body system due to its quantum fluctuations. Such a quantum phase transition can be a [[second-order phase transition]].<ref>{{cite journal|last1=Jaeger|first1=Gregg|title=The Ehrenfest Classification of Phase Transitions: Introduction and Evolution|journal=Archive for History of Exact Sciences|date=1 May 1998|volume=53|issue=1|pages=51–81|doi=10.1007/s004070050021|s2cid=121525126}}</ref> Quantum phase transitions can also be represented by the [[topological]] fermion condensation quantum phase transition, see e.g. [[strongly correlated quantum spin liquid]]. In case of [[three dimensional]]  [[Fermi liquid]], this transition transforms the [[Fermi surface]] into a Fermi volume. Such a transition can be a [[first-order phase transition]], for it transforms [[two dimensional]] structure ([[Fermi surface]]) into [[three dimensional]].  As a result, the [[topological charge]] of Fermi liquid changes abruptly, since it takes only one of a discrete set of values.