Unitary Invariants and Classification of Four-Qubit States via Negativity Fonts

S. Shelly Sharma, N. K. Sharma

Published 2012-11-10, updated 2013-02-21Version 3

Local unitary invariance and the notion of negativity fonts are used as the principle tools to construct four qubit invariants of degree 8, 12, and 24. A degree 8 polynomial invariant that is non-zero on pure four qubit states with four-body correlations and zero on all other states, is identified. Classification of four qubit states into seven major classes, using criterion based on the nature of correlations, is discussed.