Скачать или смотреть Quantum Mechanics - Time - Dependent Perturbation Theory : Harmonic Perturbation

The transition probability for a harmonic or periodic perturbation has been discussed. Such a perturbation is encountered,for instance,when charged particles (e.g.,electrons) interact with an electromagnetic field. This perturbation provokes transitions of the system from one stationary state to another. The transition probability peaks occur at the transition frequency equal to +w and -w. These are conditions for resonance which means the probability of transition is greatest only when the frequency of the perturbing field is close to the transition frequency. The result obtained for transition rate implies that the effect of harmonic perturbation is to transfer to the system,or to receive from it,a photon. In sharp contrast, constant perturbation neither transfer energy to the system nor removes energy from it. For transition into a continuum of final states the condition of detailed balancing is observed.