Maximal thermal entanglement using three-spin interactions

Jing-Heng Fu, Guo-Feng Zhang

Chun-Xian Li, Chengzhi Wang, Xiu‐Min Lin +1 more

N. Canosa, R. Rossignoli

Tomotaka Kuwahara

In the present thesis, we report several general properties of the enhancement of the entanglement by external fields. First, we investigate the thermal entanglement of interacting two qubits. We maximize it by tuning a local Hamiltonian under a given interaction Hamiltonian. We prove that the optimizing local Hamiltonian takes a simple form which dose not depend on the temperature and that the corresponding optimized thermal entanglement decays as 1/(T log T ) at high temperatures. We also find that at low temperatures the thermal entanglement is maximum without any local Hamiltonians and that the second derivative of the maximized thermal entanglement changes discontinuously at the boundary between the highand low-temperature phases. Second, we investigate the maximized entanglement of indirectly interacting two spins, that is, through other spins. We present a necessary condition for the indirect interaction to give a non-zero maximized entanglement between the focused spins. We also prove that if the focused spins are separated by two spins, there is a critical temperature above which the maximized entanglement between the focused spins vanishes. Then, we numerically calculate the maximized entanglement between the end spins of three-spin chains and four-spin chains. We discover that the maximizing local fields on the end spins have asymmetric forms. In the three-spin chains, we attribute the entanglement enhancement to the asymmetry of the local fields qualitatively and quantitatively in terms of the magnons. In XX and XY four-spin chains, we find that the critical temperature shows qualitatively different behavior depending on the conservation of the angular momentum in the z direction.

Jianping Li

Da-Chuang Li, Wei-Wei 维韦 Pan 潘, Xing-Dong 兴东 Zhao 赵 +1 more

Abstract Thermal entanglement, as influenced by interaction parameters, is investigated within the general Heisenberg XYZ model. We calculate the relationship between entanglement and the system interaction parameters, including spin–spin interaction parameters (SSIPs) and spin–orbit interaction parameters (SOIPs). By considering various parameter orientations, we identify four optimal combinations of the SSIPs and find that the optimal vector of the spin–orbit interaction aligns with the coordinate axis corresponding to the maximal SSIP component. Furthermore, we obtain three effective optimal combinations of the SOIPs corresponding to the optimal SSIPs, which can maximize the system entanglement when the parameters are tuned accordingly. To demonstrate the feasibility of our results under realistic experimental conditions, we propose an optical lattice scheme with tunable parameters.