While coarse-graining has become an increasingly powerful tool for expanding time and length scales of molecular simulation, there are numerous scenarios in which it is desirable to restore AA resolution to CG trajectories in order to develop mechanistic understanding, compute observables contingent on atomistic degrees of freedom, or develop comparisons against experimental measurements (103-112). Backmapping is a general term for the process of restoring degrees of freedom that are lost during the coarse-graining process. Early backmapping approaches followed sets of heuristics to produce a rules-based mapping from CG to AA. Initial structures are obtained either by searching fragment libraries or by a geometrically guided scheme. Structures are then refined to reduce steric clashes and unphysical bond angles and lengths, followed by optional energy minimization. (119, 120) While these approaches can be fast and produce reasonably stable AA structures, the optimization procedure can also produce unphysical dihedral angles or may fail to resolve spurious configurations such as "punched" aromatic rings. (119) Furthermore, most rules-based methods are deterministic and are therefore unable to recover the ensemble of AA structures that correspond to the one-to-many backmapping of a single CG trace.