As in the usual formulation of CTMQC, the photon-nuclear density |χ (I) (t)| 2 is reconstructed as a sum of frozen Gaussians centered at the positions of the trajectories. This calculation requires that, at the end of each dynamics step, the trajectories share information about their positions to compute the quantum momentum. Once the quantum momentum is determined, the trajectories can proceed with a new step of dynamics. On-the-fly calculation of the quantum momentum is feasible only when the trajectories are propagated simultaneously, that is why the underlying algorithm has been dubbed "coupled-trajectory"-MQC. Incorporating information about the delocalization of classical trajectories enhances the description of nonadiabatic effects, i.e., due to the electronic excited states, and of quantum effects, compared to methods such as multi-trajectory Ehrenfest (MTE) or Tully surface hopping (TSH).