Quantum Entanglement and Coherence in Molecular Magnets

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.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.

quant-pharXiv:2602.20013Journal of Magnetism and Magnetic MaterialsFeb 24, 20260 citations

Molecular nanomagnet Cu 2 + Ni 2 + Cu 2 + as a resource for bipartite and tripartite quantum entanglement and coherence

Azadeh Ghannadan, Hamid Arian Zad, Saeed Haddadi +3 more

We investigate key quantum characteristics of the mixed spin-(1/2,1,1/2) Heisenberg trimer under the influence of an external magnetic field. Specifically, we analyze the distributions of bipartite and tripartite entanglement quantified through the respective negativities and the ${l}_{1}$ -norm of coherence with the help of rigorous analytical and numerical methods. Our findings suggest that the heterotrinuclear molecular nanomagnet $[{{{\text{Cu}}^{2+}\text{L}}}_{2}{\text{Ni}}^{2+}{({\text{H}}_{2}\text{O})}_{2}]{({\text{ClO}}_{4})}_{2}\ifmmode\cdot\else\textperiodcentered\fi{}3{\text{H}}_{2}\text{O}$, which represents an experimental realization of the mixed spin-(1/2,1,1/2) Heisenberg trimer, exhibits a significant bipartite entanglement between ${\text{Cu}}^{2+}$ and ${\text{Ni}}^{2+}$ magnetic ions along with robust tripartite entanglement among all three constituent ${\text{Cu}}^{2+}{\text{Ni}}^{2+}{\text{Cu}}^{2+}$ magnetic ions. The significant bipartite and tripartite entanglement persists even at relatively high temperatures up to $37\phantom{\rule{0.16em}{0ex}}\text{K}$ and magnetic fields up to $46\phantom{\rule{0.16em}{0ex}}\text{T}$ , whereby the coherence is maintained even at elevated temperatures. It is evidenced that the aforementioned molecular complex with the magnetic core ${\text{Cu}}^{2+}{\text{Ni}}^{2+}{\text{Cu}}^{2+}$ provides an intriguing quantum resource, which exhibits a star-shaped state within the singlet eigenstate at low magnetic fields and W-like state within the triplet eigenstate at moderate magnetic fields.We investigate key quantum characteristics of the mixed spin-(1/2,1,1/2) Heisenberg trimer under the influence of an external magnetic field. Specifically, we analyze the distributions of bipartite and tripartite entanglement quantified through the respective negativities and the ${l}_{1}$-norm of coherence with the help of rigorous analytical and numerical methods. Our findings suggest that the heterotrinuclear molecular nanomagnet $[{{{\text{Cu}}^{2+}\text{L}}}_{2}{\text{Ni}}^{2+}{({\text{H}}_{2}\text{O})}_{2}]{({\text{ClO}}_{4})}_{2}\ifmmode\cdot\else\textperiodcentered\fi{}3{\text{H}}_{2}\text{O}$, which represents an experimental realization of the mixed spin-(1/2,1,1/2) Heisenberg trimer, exhibits a significant bipartite entanglement between ${\text{Cu}}^{2+}$ and ${\text{Ni}}^{2+}$ magnetic ions along with robust tripartite entanglement among all three constituent ${\text{Cu}}^{2+}{\text{Ni}}^{2+}{\text{Cu}}^{2+}$ magnetic ions. The significant bipartite and tripartite entanglement persists even at relatively high temperatures up to $37\phantom{\rule{0.16em}{0ex}}\text{K}$ and magnetic fields up to $46\phantom{\rule{0.16em}{0ex}}\text{T}$, whereby the coherence is maintained even at elevated temperatures. It is evidenced that the aforementioned molecular complex with the magnetic core ${\text{Cu}}^{2+}{\text{Ni}}^{2+}{\text{Cu}}^{2+}$ provides an intriguing quantum resource, which exhibits a star-shaped state within the singlet eigenstate at low magnetic fields and W-like state within the triplet eigenstate at moderate magnetic fields.

arXiv:2407.07037Physical Review AFeb 7, 20258 citations

{l}_{1}

-norm of coherence with the help of rigorous analytical and numerical methods. Our findings suggest that the heterotrinuclear molecular nanomagnet $[{{{\text{Cu}}^{2+}\text{L}}}_{2}{\text{Ni}}^{2+}{({\text{H}}_{2}\text{O})}_{2}]{({\text{ClO}}_{4})}_{2}\ifmmode\cdot\else\textperiodcentered\fi{}3{\text{H}}_{2}\text{O}$, which represents an experimental realization of the mixed spin-(1/2,1,1/2) Heisenberg trimer, exhibits a significant bipartite entanglement between

{\text{Cu}}^{2+}

and

{\text{Ni}}^{2+}

magnetic ions along with robust tripartite entanglement among all three constituent

{\text{Cu}}^{2+}{\text{Ni}}^{2+}{\text{Cu}}^{2+}

magnetic ions. The significant bipartite and tripartite entanglement persists even at relatively high temperatures up to

37\phantom{\rule{0.16em}{0ex}}\text{K}

and magnetic fields up to

46\phantom{\rule{0.16em}{0ex}}\text{T}

, whereby the coherence is maintained even at elevated temperatures. It is evidenced that the aforementioned molecular complex with the magnetic core

{\text{Cu}}^{2+}{\text{Ni}}^{2+}{\text{Cu}}^{2+}

provides an intriguing quantum resource, which exhibits a star-shaped state within the singlet eigenstate at low magnetic fields and W-like state within the triplet eigenstate at moderate magnetic fields.