Fermi’s golden rule is of great importance in quantum dynamics. However, in many textbooks on
quantum mechanics, its contents and limitations are obscured by the approximations and arguments in
the derivation, which are inevitable because of the generic setting considered. Here we propose to
introduce it by an ideal model, in which the quasi-continuum band consists of equaldistant levels
extending from ##IMG## [http://ej.iop.org/images/0143-0807/37/6/065406/ejpaa4187ieqn1.gif] {$-\infty
$} to ##IMG## [http://ej.iop.org/images/0143-0807/37/6/065406/ejpaa4187ieqn2.gif] {$+\infty $} , and
each of them couples to the discrete level with the same strength. For this model, the transition
probability in the first order perturbation approximation can be calculated analytically by invoking
the Poisson summation formula. It turns out to be a piecewise linear function of time, demonstrating
on the one hand the key features of Fermi’s golden…