Generation of squeezed light via spontaneous emission from a three-level cascade system

Abstract

A theoretical investigation is made into the possibility of generating squeezed states of light in spontaneous emission from a three-level atom. Spontaneous emission is known as a source of the noise which destroys coherence effects. We find that rather than destroy squeezing, spontaneous emission from a three-level cascade system can actually create squeezing in an initially unsqueezed source field provided the atom is initially prepared in a suitable superposition of its states. We show that the ability of a three-level atom to generate squeezing of the source field via spontaneous emission relies on the presence of non-zero two-photon coherences that are not present in two-level atoms, in which source field squeezing only occurs if it is present initially.