Vortex light bullets in Rydberg atoms trapped in twisted PT-symmetric waveguide arrays

We present a theoretical scheme for generating vortex light bullets (LBs) in a Rydberg atomic system. The stability property and propagation dynamics of vortex LBs with different topological charges are investigated in twisted circular waveguide arrays with a parity-time ($\mathcal{PT}$) symmetry. The numerical solutions of the corresponding nonlinear Schrödinger equation are obtained by the modified square operator method and split-step Fourier method. The longitudinal twist changes the stabilities of six-core vortex LBs and enriches the modulation diversity as the states with the opposite charges degenerate by the introducing of rotation frequency. Specifically, we reveal that the energy exchange between waveguides and media gives rise to the formation of necklace breathers, which is crucial for implementing light storage. These unique characteristics arise from the balance or quasibalance among the rotation frequency, the Rydberg-Rydberg interaction, and the nonequivalent gain/loss distribution along the azimuthal direction. We thus provide examples of robust high-charge vortex LBs and necklace breathers in the Rydberg atomic system with a $\mathcal{PT}$ symmetry.