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.

• Received 22 June 1978

DOI:https://doi.org/10.1103/PhysRevA.18.2217