Abstract:
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 | S, M>, 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.
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Received 9 May 2001 and Received in final form 16 November 2001
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Wang, X., Mølmer, K. Pairwise entanglement in symmetric multi-qubit systems. Eur. Phys. J. D 18, 385–391 (2002). https://doi.org/10.1140/epjd/e20020045
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DOI: https://doi.org/10.1140/epjd/e20020045