In quantum mechanics, momentum (like all other physical variables) is defined as an operator, which "acts on" or pre-multiplies the wave function ψ(r, t) to extract the momentum eigenvalue from the wave function: the momentum vector a particle would have when measured in an experiment. The momentum operator is an example of a differential operator.
的动量算符可以写为
；
是动量算符，
是约化普朗克常数，
是虚数单位，
是位置。
；
是动量。