We consider a two-dimensional (2D) trapped ion model in which two laser beams drive the corresponding vibrational motions and are carrier resonant with the two-level of the ion. Due to the coherent superposition of two sub-Rabi oscillations involved in the bimodal vibrations, the Rabi frequency degeneration and offset may occur in this model. This provides the possibility of generating the pair coherent state in the 2D trapped ion.
Wang, K-G., Maniscalco, S., Napoli, A., & Messina, A. (2001). Generation of pair coherent states in two-dimensional trapped ion. Chinese Physics Letters, 18(3), . https://doi.org/10.1088/0256-307X/18/3/319