In Fig. the distributions of momenta are shown at times t = 10, 50, 100 fs along the dynamics. In the upper panels, CT-MQC distributions (blue dots) are compared to the quantum trajectories (lilac dots), whereas, in the lower panels, CT-TSH distributions (orange dots) are compared to the quantum trajectories. In both cases a clear qualitative difference is observed, which follows from the different initial momenta used for the quantum and for the coupled trajectories. In CT-MQC and CT-TSH positions and momenta are independent variables, and thus they are randomly sampled from uncorrelated (Wigner-transformed) positions-momenta distributions. Note that the distributions are uncorrelated since the (quantum) initial density is a two-dimensional Gaussian in the variables ϕ and q. Figure shows that the momenta distribution of quantum trajectories is much more localized along P q than the distributions of coupled trajectories, whereas they have comparable widths along P ϕ at time t = 10 fs (left panels). The momenta of the quantum trajectories rapidly increase only along P ϕ , and the distribution in this direction at time t = 50 fs (central panels) is as broad as CT-MQC and CT-TSH. At later times, t = 100 fs in the figure (right panel), the distributions of all ensembles of trajectories have comparable broadening along P ϕ . However, quantum trajectories remain extremely localized in momentum space along P q if compared to CT-MQC and CT-TSH.