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. 2015 Nov 9;5:16231. doi: 10.1038/srep16231

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Copyright © 2015, Macmillan Publishers Limited

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(a) Comparison of the numerically computed von Neumann entropy (empty circles) of the reduced density matrix of the chain minimized over the atom index and the analytical expression for the entropy of the Dicke state (green circles), both for excitations n = 1 and as a function of the atom number at distance a = 0.1 λ₀. (b) Depth of entanglement of the subradiant four-atom state (blue dot) prepared by the magnetic field gradient scheme (see Fig. 2e). It clearly lies above the k = 3 boundary indicating four-atom entanglement. The -atom entanglement boundaries of the target state population as a function of the ground state population have been computed for the corresponding target state of a four-atom chain at distance a = 0.025 λ₀.

Inline graphic — (a) Comparison of the numerically computed von Neumann entropy (empty circles) of the reduced density matrix of the chain minimized over the atom index and the analytical expression for the entropy of the Dicke state (green circles), both for excitations n = 1 and as a function of the atom number at distance a = 0.1 λ₀. (b) Depth of entanglement of the subradiant four-atom state (blue dot) prepared by the magnetic field gradient scheme (see Fig. 2e). It clearly lies above the k = 3 boundary indicating four-atom entanglement. The -atom entanglement boundaries of the target state population as a function of the ground state population have been computed for the corresponding target state of a four-atom chain at distance a = 0.025 λ₀.