Pairwise entanglement in symmetric multi-qubit systems
Institute of Physics and Astronomy, University of Aarhus, 8000 Aarhus C, Denmark
Corresponding author: a email@example.com
Revised: 16 November 2001
Published online: 15 March 2002
For pairs of particles extracted from a symmetric state of N two-level systems, the two-particle density matrix is expressed in terms of expectation values of collective spin operators for the large system. Results are presented for experimentally relevant examples of pure states: Dicke states , spin coherent, and spin squeezed states, where only the symmetric subspace, S=N/2 is populated, and for thermally entangled mixed states populating also lower S values. The entanglement of the extracted pair is then quantified by a calculation of the concurrence, which provides directly the entanglement of formation of the pair.
PACS: 03.65.Ud – Entanglement and quantum nonlocality (e.g. EPR paradox, Bell's inequalities, GHZ states, etc.) / 03.67.Lx – Quantum computation / 75.10.Jm – Quantized spin models
© EDP Sciences, Società Italiana di Fisica, Springer-Verlag, 2002