Editing Statistical mechanics (section)

===Quantum statistical mechanics===
{{main|Quantum statistical mechanics}}
[[Quantum statistical mechanics]] is [[statistical mechanics]] applied to [[quantum mechanics|quantum mechanical systems]]. In quantum mechanics, a [[statistical ensemble (mathematical physics)|statistical ensemble]] (probability distribution over possible [[quantum state]]s) is described by a [[density matrix|density operator]] ''S'', which is a non-negative, [[self-adjoint]], [[trace-class]] operator of trace 1 on the [[Hilbert space]] ''H'' describing the quantum system.  This can be shown under various [[mathematical formulation of quantum mechanics|mathematical formalisms for quantum mechanics]].  One such formalism is provided by [[quantum logic]].{{fact|date=April 2024}}