  Numerical studies of lattice quantum field theories are conducted in finite
spatial volumes, typically with cubic symmetry in the spatial coordinates.
Motivated by these studies, this work presents a general algorithm to construct
multi-particle interpolating operators for quantum field theories with cubic
symmetry. The algorithm automates the block diagonalization required to combine
multiple operators of definite linear momentum into irreducible representations
of the appropriate little group. Examples are given for distinguishable and
indistinguishable particles including cases with both zero and non-zero spin.
An implementation of the algorithm is publicly available at
https://github.com/latticeqcdtools/mhi.
