Editing Adiabatic theorem (section)

{{Short description|Concept in quantum mechanics}}
{{about|the adiabatic theorem in quantum mechanics|adiabatic processes in thermodynamics|adiabatic process}}

The '''adiabatic theorem''' is a concept in [[quantum mechanics]]. Its original form, due to [[Max Born]] and [[Vladimir Fock]] (1928), was stated as follows:
:''A physical system remains in its instantaneous [[eigenstate]] if a given [[perturbation theory (quantum mechanics)|perturbation]] is acting on it slowly enough and if there is a gap between the [[eigenvalue]] and the rest of the [[Hamiltonian (quantum mechanics)|Hamiltonian]]'s [[Spectrum of an operator|spectrum]].''<ref name="Born-Fock">{{cite journal |author=Born |first=M. |last2=Fock |first2=V. A. |name-list-style=and |year=1928 |title=Beweis des Adiabatensatzes |journal=Zeitschrift für Physik A |volume=51 |issue=3–4 |pages=165–180 |bibcode=1928ZPhy...51..165B |doi=10.1007/BF01343193 |s2cid=122149514}}</ref>
In simpler terms, a quantum mechanical system subjected to gradually changing external conditions adapts its functional form, but when subjected to rapidly varying conditions there is insufficient time for the functional form to adapt, so the spatial probability density remains unchanged.