Читать книгу Quantum Mechanics, Volume 3 - Claude Cohen-Tannoudji - Страница 145

As for the time derivative term, the function it contains can be written as:

(26)

In this summation, all terms involving the individual states j other than the state i (which is undergoing the derivation) lead to an expression of the type:

(27)

which equals 1 since this expression is the square of the norm of the state , which is simply the Fock state |nj = 1〉. As for the state i, it leads to a factor written in the form of a scalar product in the one-particle state space:

(28)