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.