In this paper, we study the influence of anisotropy on the usefulness, of the entanglement in a two-qubit Heisenberg XY chain at thermal equilibrium in the presence of an external magnetic field, as resource for quantum teleportation via the standard teleportation protocol. We show that the nonzero thermal entanglement produced by adjusting the external magnetic field strength beyond some critical strength is a useful resource. We also considered entanglement teleportation via two two-qubit Heisenberg XY chains.
In this paper we study the influence of anisotropy on the usefulness of the entanglement in a two-qubit Heisenberg XY chain at thermal equilibrium in the presence of an external magnetic field, as a resource for quantum teleportation via the standard teleportation protocol. We show that the nonzero thermal entanglement produced by adjusting the external magnetic field beyond some critical strength is a useful resource. We also consider entanglement teleportation via two two-qubit Heisenberg XY chains.
We study the probabilistic (conditional) teleportation protocol when the entanglement needed for its implementation is given by thermal entanglement, i.e., when the entangled resource connecting Alice and Bob is an entangled mixed state described by the canonical ensemble density matrix. Specifically, the entangled resource we employ here is given by two interacting spin-
21 systems (two qubits) in equilibrium with a thermal reservoir at temperature
T. The interaction between the qubits is described by a Heisenberg-like Hamiltonian, encompassing the Ising, the
XX, the
XY, the
XXX, and
XXZ models, with or without external fields. For all those models, we show analytically that the probabilistic protocol is exactly equal to the deterministic one whenever we have no external field. However, when we turn on the field, the probabilistic protocol outperforms the deterministic one in several interesting ways. Under certain scenarios, for example, the efficiency (average fidelity) of the probabilistic protocol is greater than the deterministic one and increases with increasing temperature, a counterintuitive behavior. We also show regimes in which the probabilistic protocol operates with relatively high success rates and, at the same time, with efficiency greater than the classical limit
2/3, a threshold that cannot be surpassed by any protocol using only classical resources (no entanglement shared between Alice and Bob). The deterministic protocol's efficiency under the same conditions is below
2/3, highlighting that the probabilistic protocol is the only one yielding a genuine quantum teleportation. We also show that near the quantum critical points for almost all those models the qualitative and quantitative behaviors of the efficiency change considerably, even at finite
T.
We consider a two-qubit Heisenberg XXZ chain as a resource for quantum teleportation via the standard teleportation protocol T 0 . The effects of anisotropic on teleportation fidelity and entanglement are studied in detail. We find anisotropic not only improves the critical temperature T c and critical magnetic field B c , beyond which quantum teleportation is inferior to classical communication protocol, but also enhances the fidelity for fixed magnetic field B and temperature T. For entanglement teleportation, the effects of magnetic field on average fidelity and output entanglement are studied.
Quantum entanglement is studied NMR multipulse spin locking, when a system of spins coupled by the dipole–dipole interaction in a strong magnetic field is irradiated by a sequence of resonant high-frequency
φ -pulses with the same time delay
2τ between successive pulses. For times
t∼T2 (
T2≈ωloc−1 ,
ωloc is determined by the dipole–dipole interaction), quasi-equilibrium with a structure depending on the relation between the pulsed field
ω1=φ/2τ and
ωloc is established in the system. For
ω1⪅ωloc , a one-temperature quasi-equilibrium state arises, while a quasi-equilibrium with the dipole and Zeeman temperatures appears for
ω1≫ωloc . The temperature dependence of entanglement is investigated for
ω1⪅ωloc . For
ω1≫ωloc , the further evolution of the system is determined by the Provotorov equations and leads to the equalization of the dipole and Zeeman temperatures. It is shown that the entanglement is absent in this case.
In this paper we study the entanglement in a two-qubit spin in the XYZ model, and teleport a two-qubit entangled state using this spin chain in the condition of the thermal equilibrium as a quantum channel. We investigate the effects of the interaction of z-component JZ, the inhomogeneous magnetic field b, the anisotropy ?, and the temperature T on the entanglement and fidelity. In order to characterize the quality of the teleported state, we research the average fidelity Fa. High average fidelity of the teleportation is obtained when the temperat ure is very low. Under some condition, we also find that when inhomogeneity increases to a certain value, the average fidelity can exhibit a larger revival than that for less values of b.