Anticoherence in cavity QED systems: Influence from the associated baths beyond a Born approximation

Abstract

The influence of the associated bath beyond a Born approximation (BA) is studied in a basic cavity QED system, i.e., the Rabi model coupled to a bath. It is shown that the application of a BA is valid only at zero temperature for all the baths, including the vacuum field and phonon bath associated with the two-state system, as well as the dissipative bath associated with the monochromatic optical mode. The non-BA process brings a different type of influence which stems from the inherent coupling between the quantum system and the associated bath and is against the building up of the dressed state. The physics behind this type of influence, which we term anticoherence, is analyzed, and a complete picture of influence from the associated bath is developed. To find the observed spectrum beyond a BA, we use the small-polaron theory to examine the state evolution under Fermi's golden rule, and based on it, the contribution from both the BA and non-BA processes can be calculated. The obtained result can help one to understand some peculiar observations in the strong-coupling regime.