Does the Berry phase in a quantum optical system originate from the rotating wave approximation?

• Non-zero Berry phases for the Rabi model (without rotating wave approximation) are verified.
• A general formulation of Berry phases for both the JC model and the Rabi model is presented.
• The claim of vanishing Berry phase in the Rabi model is a result of improper semiclassical approximation.
• Analytic solutions for the Rabi model is presented in the semiclassical approximation.

The Berry phase (BP) in a quantized light field demonstrated more than a decade ago (Fuentes-Guridi et al., 2002 [9]) has attracted considerable attention, since it plays an important role in the cavity quantum electrodynamics. However, it is argued in Larson (2012) [15] that such a BP is just due to the rotating wave approximation (RWA) and the relevant BP should vanish beyond this approximation. Based on a consistent analysis we conclude in this letter that the BP in a generic Rabi model actually exists, no matter whether the RWA is applied. The existence of BP is also generalized to a three-level atom in the quantized cavity field.