An elementary formula for the von Neumann and Rényi entropies describing quantum correlations in two-fermionic systems having four single-particle states is presented. An interesting geometric structure of fermionic entanglement is revealed. A connection with the generalized Pauli principle is established.

• Received 25 January 2005

DOI:https://doi.org/10.1103/PhysRevA.72.022302