Energy levels of and states and multi-photon transitions for angle θ from the rotation axis (-axis) under the rotation of the direction of the magnetic field at a frequency . Here denotes the resonance frequency of the radio-frequency field for sideband resonance with and is the fixed microwave frequency with a linear polarization along the axis. Case (ii) is also applied for π/2< θ < π.
Shift of the frequency separation between the and states under the rotation of the magnetic field with constant frequency from that under the static magnetic field, as a function of angle θ from rotation axis ( axis). The solid curve is the time derivative of the Berry phase.