  Classification of different forms of quantum entanglement is an active area
of research, central to development of effective quantum computers, and similar
to classification of error-correction codes, where code duality is broadened to
equivalence under all 'local' unitary transforms. We explore links between
entanglement, coding theory, and sequence design, by examining multi-spectra of
quantum states under local unitary action, and show that optimal
error-correcting codes and sequences represent states with high multiparticle
entanglement.
