Fractional quantum Hall (FQH) systems are strongly interacting electron systems with topological order. These systems are characterized by novel ground states and fractionally charged and neutral excitations. The neutral excitations are dominated by a low-energy collective magnetoroton mode. Here, we derive and use a quasi-one-dimensional model to investigate the ultrafast nonequilibrium dynamics of a laser-driven FQH system within a two-Landau-level approximation. As opposed to traditional and synthetic bilayers, our model accounts for interactions where electrons can scatter from one Landau level to another. By performing exact time evolution of the system, we create an out-of-equilibrium state following the laser pulse that exhibits a rich set of nonequilibrium phenomena. Our calculations show the presence of nontrivial excited modes. One of these modes is electromagnetically active and represents density oscillations of the magnetoplasmon mode. Another mode is identified by evaluating the overlap between the initial ground state and the nonequilibrium state. This mode is analogous to the chiral-graviton mode for FQH systems recently measured in experiments [Liang et al., Nature (London) 628, 78 (2024)]. Our results show that a linearly polarized pulse field can excite the graviton mode when inter-Landau-level scattering occurs.

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• Fractional quantum Hall effect
• Landau levels
• Ultrafast phenomena