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 spin orientation σ_x for different parameters: (a) , Ω = 0.5, (b) , Ω = 5, (c) , g = 0.2, (d) g = 0.5, Ω = 0.1.