Thermal quantum correlations in a three-qubit spin chain under an in-homogeneous magnetic field
Abstract
The thermal quantum correlations of a three-qubit spin chain of XY type under an in-homogeneous magnetic field have been investigated, where by considering magnetic fields with different magnitudes ℬ−b, ℬ and ℬ+b for each spin, the quantum correlations between the adjacent and the non-adjacent qubits (spins) have been studied. For this purpose, the concurrence as an entanglement quantifier and the trace distance discord as a discord-like quantifier have been computed for the corresponding bipartite subsystems with the reduced density matrices ρ(12), ρ(23) and ρ(13). The differences between the concurrence and the trace distance discord, are explained in detail. Their dependence on the parameters of the uniform magnetic field ℬ, the temperature T, and the in-homogeneity parameter b is discussed so that the thermal correlation decreases by increasing the mentioned parameters. Also, the results show that by changing and controlling the parameters ℬ, T and b, especially the in-homogeneous magnetic field b, it is possible that the correlation value between non-adjacent spins, i.e. c(ρ(13)) can be reached to a greater value than the thermal correlations between adjacent spins, i.e. c(ρ(12)) and c(ρ(23)). Moreover, it is shown that the trace distance D(13)T(ρ) between the non-adjacent spins has always a lower value than those of the adjacent spins D(12)T(ρ) and D(23)T(ρ). Finally, the results show that in-homogeneous magnetic field b can be effective for improving thermal quantum correlation.
