2 Quantum theory of radiation

Xie Li-Jun, Deng-Yu Zhang

The interaction between radiation and two-level atom was investigated by semi-classical theory and quantum theory respectively.The fidelity of the two-level atom's quantum state was written out, The influences of the radiation intensity in the case of semi-classical theory and the photon number of the radiation in the case of quantum theory on the fidelity were discussed for different atomic initial states.It is found that the fidelity of quantum state is independent of radiation intensity when the atom is initially in a superposition state and the atom interacts resonantly with the radiation field in semi-classical theory. The atom's quantum fidelity evolves periodically with time,and its frequency is modulated by radiation intensity.Furthermore,it can effectively change quantum information fidelity when the appropriate detuning is selected.

Norbert Straumann

In this contribution I discuss a peak in Einstein's endeavor to extract as much information as possible about the nature of radiation from the Planck distribution is his paper "On the Quantum Theory of Radiation" of 1916. This is one of the most important contributions of Einstein to quantum theory.

Alberto Galindo, P. Pascual

Steven Weinberg

Igor I Sobel'man, Igor Viktorovich Tyutin

It is pointed out that induced radiation effects cannot be purely quantum in nature and that they must be present in the classical theory of radiation processes. The classical theory is usually built on the example of the harmonic oscillator. Several effects arising from the interaction of the oscillators with the field disappear when harmonic oscillators are considered. This is particularly true when one is concerned with radiation processes induced by the field. In addition, the interaction between the field and the radiation of nonlinear oscillators (their frequencies depend on the energy) was not previously considered from the standpoint of the classical theory. Because of these reasons and because of the interest in the problem of quantum generators the question of the role of induced radiation in classicai theory was examined. The theory is described, and some specific properties of the classical system are contrasted with those of the quantum system. The description includes a discussion of spontaneous radiation processes and both harmonic and anharmonic oscillators are considered. The limiting transition from quantum to classical theory is discussed, and a detailed comparison of the two more » theories is made. An ensemble of oscillators distributed in energy is discussed in the classical theory. It is shown, for certaln determined conditions, that classical systems do not absorb but rather enhance incident radiation. (TTT) « less