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In this third of a series on quantum radiation, we explore the feasibility ofusing the memories kept in a quantum field to decipher certain informationabout the early universe. As a model study, we let a massless quantum field besubjected to a parametric process for a finite time interval such that the modefrequency of the field transits from one constant value to another. Thisconfiguration mimics a statically-bounded universe, but not a continuouslyevolving one. The field squeezed by this process should contain information ofthe process itself. If an atom is coupled to the field after the parametricprocess, its response will depend on the squeezing, and any quantum radiationemitted by the atom will carry this information away so that an observer at amuch later time may still identify it. Our analyses show that 1) a remoteobserver cannot measure the generated squeezing via the radiation energy fluxfrom the atom because the net radiation energy flux is canceled. However, 2)there is a chance to identify squeezing by measuring the constant radiationenergy density at late times. The only restriction is that this energy densityis of the near-field nature. The second part of this paper focuses on 3) thedependence of squeezing on the functional form of the parametric process. Viaseveral examples we demonstrate that the behavior of squeezing reflectessential properties of the parametric process. In fact, striking features mayshow up in complicated processes involving various scales. These analyses allowus to establish the connection between properties of a squeezed quantum fieldand the parametric process which does the squeezing. Therefore, 4) one canconstruct templates to reconstitute the unknown parametric processes from thedata of measurable quantities subjected to squeezing. In a sequel paper theseresults will be applied to a study of quantum radiations in cosmology.

Fluctuations-Induced Quantum Radiation and Reaction from an Atom in a Squeezed Quantum Field