Purified Projection Method and Uhlmann Fidelity for Mixed Hartree Dynamics

We give a purification and fidelity formulation of the projection method for mixed Hartree data. For the mean-field evolution of $N$-particle density matrices, we prove quantitative propagation of chaos for all fixed marginals, first in squared Uhlmann fidelity and then in trace norm via the Fuchs–van de Graaf inequality. The argument applies a rank-one Pickl-type counting estimate in a purified one-particle space and uses monotonicity of fidelity under partial trace to return to the physical variables. The result allows singular interactions satisfying a projected-square bound, including $L^{2r}$ interactions and the Coulomb potential.