Investigation of the time correlation of photons emitted by excited argon atoms

Yu.F. Skachkov

M. Dagenais, L. Mandeļ

Two-time correlations in the emissions of photons by a single atom of sodium in the presence of a coherent exciting field near resonance have been investigated. In the experiment sodium atoms in an atomic beam are excited by a perpendicular light beam from a tunable dye laser, and they are prepared by optical pumping to behave as two-level quantum systems. The fluorescent light is collected by a microscope objective in a direction that is approximately orthogonal to both beams and imaged on two photomultipliers. Photoelectric pulse correlations are measured in the presence of exciting fields of various strengths and for various detunings from the atomic resonance, and are found to exhibit significant nonclassical features. The results show clearly that the emitted photons exhibit antibunching, in good quantitative agreement with the predictions of quantum electrodynamics.

Carl A. Kocher

Pavel A Apanasevich, S. Ya. Kilin, A F Fedorov

It is shown that analysis of the spectral time correlations of resonantly scattered photons is a new Doppler-free method for the investigating excited states of atoms and molecules. By using this method for investigation of the photon correlation, the times of transitions between excited states can be measured. Unlike the usual method of the delayed fluorescence the measurement can be accomplished with a continuous excitation of upper levels.

P. Hraskó

S. Swain, Peng Zhou, Z. Ficek

We investigate the two-time intensity correlation functions of the fluorescence field emitted from a $V$-type three-level atom. We are particularly interested in the manner in which the atom emits photons in the presence of quantum interference. We show that under strong-field excitation quantum interference leads to anticorrelations of photons emitted from the atomic excited levels which can exist for extremely long times. This indicates that the excited atomic levels are not the preferred radiative states. We find that the atom spends most of its time in a superposition of the excited atomic levels from which it emits strongly correlated photons. The strong correlations are present only for a nonzero splitting between the excited levels, and for degenerate levels the correlations reduce to that of a two-level atom. Moreover, we find that the transition from the ground level to the symmetric superposition of the excited levels does not saturate even for a strong driving field. We also calculate the correlation functions for a weak driving field, and find that in this case the photon correlations are not significantly affected by quantum interference, but the atom can emit a strongly correlated pair of photons produced by a three-wave mixing process. Under appropriate conditions, with near-maximal quantum interference, it is possible to make the maximum value of the correlation function extremely large, in marked contrast with the corresponding case with no quantum interference.