Stark-induced tunable phase transition in the two-photon Dicke-Stark model
Phys. Rev. A 112, 013720 – Published 24 July, 2025
DOI: https://doi.org/10.1103/vqnf-zd5w
Abstract
We theoretically investigate the superradiant phase transition (SPT) in the two-photon Dicke-Stark model, which incorporates both Rabi and Stark coupling. By introducing a Stark coupling term, we significantly reduce the critical Rabi coupling strength required to achieve the SPT, enabling it to occur even in non-ultrastrong-coupling regimes. Using mean-field theory, we derive the conditions for the SPT and show that it exhibits a second-order phase transition. Surprisingly, we demonstrate that the transition point can be widely tuned by the Stark coupling strength. The signatures of these Stark-tunable SPT points manifest through atomic pseudospin mean values. When quantum fluctuations are included, the spin-squeezing distributions also reveal the effects of Stark-tunable SPT points. In addition, we propose an experimentally feasible realization using an ion-trap system driven by three lasers. Our scheme enables optical switching between normal and superradiant phases through pump field intensity modulation, where the Stark coupling coefficient serves as the optically tunable parameter. Our results offer an alternative approach to engineer the SPT, extending superradiance-based quantum technologies beyond the ultrastrong-coupling regime.
