J. M. Matera

Entanglement of finite cyclic chains at factorizing fields

We examine the entanglement of cyclic spin 1/2 chains with anisotropic XY Z Heisenberg couplings of arbitrary range at transverse factorizing magnetic fields. At these fields the system exhibits a degenerate symmetry-breaking separable ground state (GS). It is shown, however, that the side limits of the GS pairwise entanglement at these fields are actually non-zero in finite chains, corresponding such fields to a GS spin-parity transition. These limits exhibit universal properties like being independent of the pair separation and interaction range, and are directly related to the magnetization jump. Illustrative exact results are shown for chains with I) full range and II) nearest neighbor couplings. Global entanglement properties at such points are also discussed.

Factorization and entanglement in generalXYZspin arrays in nonuniform transverse fields

We determine the conditions for the existence of a pair of degenerate parity breaking separable eigenstates in general arrays of arbitrary spins connected through XYZ couplings of arbitrary range and placed in a transverse field, not necessarily uniform. Sufficient conditions under which they are ground states are also provided. It is then shown that in finite chains, the associated definite parity states, which represent the actual ground state in the immediate vicinity of separability, can exhibit entanglement between any two spins regardless of the coupling range or separation, with the reduced state of any two subsystems equivalent to that of pair of qubits in an entangled mixed state. The corresponding concurrences and negativities are exactly determined. The same properties persist in the mixture of both definite parity states. These effects become specially relevant in systems close to the XXZ limit. The possibility of field induced alternating separable solutions with controllable entanglement side limits is also discussed. Illustrative numerical results for the negativity between the first and the j{sup th} spin in an open spin s chain for different values of s and j are as well provided.

Thermal entanglement in fully connected spin systems and its random-phase-approximation description

We examine the thermal pairwise entanglement in a symmetric system of

Separability and entanglement in finite dimer-type chains in general transverse fields

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Description of thermal entanglement with the static path plus random-phase approximation

spins fully connected through anisotropic

Evaluation of pairwise entanglement in translationally invariant systems with the random phase approximation

XYZ

Pair entanglement in dimerized spin-s chains

-type couplings embedded in a transverse magnetic field. We consider both the exact evaluation together with that obtained with the static path + random phase approximation (RPA) and the ensuing mean field + RPA. The latter is shown to provide an accurate analytic description of both the parallel and antiparallel thermal concurrence in large systems. We also analyze the limit temperature for pairwise entanglement, which is shown to increase for large fields and to decrease logarithmically with increasing

Generalized mean-field description of entanglement in dimerized spin systems

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Entanglement and area laws in weakly correlated Gaussian states

. Special finite size effects are as well discussed.

Factorization and entanglement in general XYZ spin arrays in nonuniform transverse fields

We determine the conditions under which general dimer-type spin chains with