We investigate the equilibrium quantum phase transition and critical phenomena in a Tavis-Cummings model that incorporates both an antisqueezing term and the $A^2$ term (the square of the vector potential). The antisqueezing term substantially reduces the critical coupling required for the phase transition, enabling the transition to occur without the need for ultrastrong atom-field coupling. Interestingly, when the $A^2$ term is included, the transition displays a reversed directionality: as the atom-field coupling increases, the system transitions from the superradiant phase back to the normal phase. We find that both ground-state entanglement and quantum superposition display correspondingly reversed behavior in the presence of the $A^2$ term. Moreover, we show that this reversed phase transition is accompanied by a dynamic crossover from chaotic to integrable behavior.

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• Cavity quantum electrodynamics
• Quantum optics