An analytical variational method for the biased quantum Rabi model in the ultra-strong coupling regime

Mao Bin-Bin¹, Liu Maoxin², Wu Wei², Li Liangsheng³, Ying Zu-Jian⁴, Luo Hong-Gang^{1, 2, †}

(color online) The ground state energy of the system with different parameters: (a) , Ω = 1, (b) , Ω = 2.