Classification of Four-Qubit States by Means of a Stochastic Local Operation and the Classical Communication Invariant

It is a recent observation that entanglement classification for qubits is closely related to stochastic local operations and classical communication(SLOCC)invariants.Verstraete et al.[Phys.Rev.A 65(2002)052112]showed that for pure states of four qubits there are nine different degenerate SLOCC entanglement classes.Li et al.[Phys.Rev.A 76(2007)052311]showed that there are at least 28 distinct true SLOCC entanglement classes for four qubits by means of the SLOCC invariant and semi-invariant.We give 16 different entanglement classes for four qubits by means of basic SLOCC invariants.