Entanglement of electron pairs extracted from a many-body systemA. Ramsak1, 2, J. Mravlje2, T. Rejec1, 2 and A. Lautar1
1 Faculty of Mathematics and Physics, University of Ljubljana - Ljubljana, Slovenia, EU
2 Jožef Stefan Institute - Ljubljana, Slovenia, EU
received 10 February 2009; accepted in final form 29 April 2009; published May 2009
published online 29 May 2009
Entanglement of spins is analyzed for two electrons extracted from a mixed many-electron state by projecting onto the two-electron subspace. The concurrence formulae are expressed in a compact form for states with a well-defined square of the total spin projection. As an example, the thermal entanglement for a qubit pair with an anisotropic Heisenberg and the Dzyaloshinskii-Moriya interactions in an inhomogeneous magnetic field is given analytically. Remarkably, the concurrence of a pair of electrons with antiparallel spins and in a delocalised orbital state is given by the scalar product of the state with its spin-flipped state and not with the time-reversed state.
03.67.Mn - Entanglement measures, witnesses, and other characterizations.
73.21.La - Quantum dots.
03.67.Bg - Entanglement production and manipulation.
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