Quantum correlation and coherence in a mononuclear nickel-based molecular Magnet

Abstract

We investigate the behaviors of thermal entanglement, quantum correlation beyond entanglement namely, measurement-induced nonlocality (MIN) and coherence in a nickel radical molecular magnet (Et3NH)[Ni(hfac)2L], whose spin-spin interactions are well described by the Heisenberg model. Using experimentally estimated coupling parameters, we compute the thermal state of the system and analyze the dependence of quantum resources on temperature and magnetic field. The results indicate that the quantum resources of the nickel-radical molecular magnet persist even at room temperature. We show that while negativity (the entanglement measure) rapidly vanishes with increasing temperature and magnetic field, measurement-induced nonlocality and quantum coherence remain comparatively more stable and persist in regions where entanglement is absent. These results highlight the significance of nonclassical correlations beyond entanglement in thermally activated spin systems and suggest that such molecular magnets could serve as viable platforms for quantum information processing in realistic conditions.

Figures (4)

• Figure 1: Schematic representation of the nickel-radical molecular complex $(Et_3NH)[Ni(hfac)_2L]$Spinu2021
• Figure 2: Variations of quantum resources such as (a) negativity (b) MIN and (c) $l_1-$norm of coherence as a function of temperature at a few selected values of the external magnetic field for the nickel-radical molecular compound described by the Hamiltonian (1) with the parameters set $J/k_B = 505 K$, $g_{Rad} = 2.005$, and $g_{Ni} = 2.275$.
• Figure 3: Variations of quantum resources such as (a) negativity (b) MIN and (c) $l_1-$norm of coherence as a function of magnetic field at a few selected values of the temperature for the nickel-radical molecular compound given by the Hamiltonian (1) with the parameters set $J/k_B = 505 K$, $g_{Rad} = 2.005$, and $g_{Ni} = 2.275$.
• Figure 4: Density plots of the (a) negativity, (b) MIN, and (c) $l_1-$norm of cohrence in the temperature versus magnetic field plane for the mixed spin-( 1/2 ,1) Heisenberg dimer given by the Hamiltonian (1) with the parameter set $J/k B = 505 K$, $g_{Rad} = 2.005$, and $g_{Ni} = 2.275$ adjusted to a theoretical modeling of the molecular complex $(Et_3 NH)[Ni(hfac)_2 L]$. (a) shows a detail of the density plot for the negativity), while (b) shows a complete density plot up to magnetic fields above which the negativity vanish