Molecular Nanomagnet CuIINiIICuII as Resource for Quantum Entanglement, Coherence, and Spin Squeezing

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, the l₁-norm of coherence, and spin squeezing with the help of rigorous analytical and numerical methods. Our findings suggest that the heterotrinuclear molecular nanomagnet [\₂NiII(H₂O)₂](ClO₄)₂3H₂O, which represents an experimental realization of the mixed spin-(1/2,1,1/2) Heisenberg trimer, exhibits a significant bipartite entanglement between CuII and NiII magnetic ions along with robust tripartite entanglement among all three constituent magnetic ions. The significant bipartite and tripartite entanglement persists even at relatively high temperatures up to 37\,K and magnetic fields up to 50\,T, whereby the coherence is maintained even at elevated temperatures. In addition, we investigate the spin squeezing parameter within thermal states of the spin-(1/2,1,1/2) Heisenberg trimer. Our exact results reveal optimal conditions for achieving the highest degree of the spin squeezing, which are achieved at zero magnetic field around T ≈ 30\,K.