Local Unitary Equivalence of Tripartite Quantum States In Terms of Trace Identities

In this paper we present a modified version of the proof given Jing-Yang-Zhao's paper "Local Unitary Equivalence of Quantum States and Simultaneous Orthogonal Equivalence," which established the correspondence between local unitary (LU) equivalence and simultaneous orthogonal equivalence of bipartite quantum states. Our modified proof utilizes a hypermatrix algebra framework, and with this framework we are able to generalize this correspondence to tripartite quantum states. Finally, we apply a generalization of Specht's criterion proved in Futorny-Horn-Sergeichuk' paper "Specht's Criterion for Systems of Linear Mappings" to essentially reduce the problem of local unitary equivalence of tripartite quantum states to checking trace identities and a few other LU invariants. We also note that all of these results can be extended to arbitrary multipartite quantum states, however there are some practical limitations.