Abstract In a recent paper [Phys. Rev. A 76 042313 (2007)], Sainz and Bjork introduced an entanglement invariant $\mathcal{E}$ under evolution for a system of four qubits interacting through two isolated Jaynes-Cummings Hamiltonians. This paper proves that this entanglement invariant $\mathcal{E}$ is closely connected with the linear entropy between two independent subsystems.
Received: 25 March 2008
Revised: 22 April 2008
Accepted manuscript online:
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