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 E₀ for different parameters: (a) , Ω = 0.5, (b) , Ω = 5, (c) , g = 0.5, (d) g = 0.2, Ω = 5.