Emergence of Spinmerism for Molecular Spin‐Qubits Generation**

Abstract

Molecular platforms are regarded as promising candidates in the generation of units of information for quantum computing. Herein, a strategy combining spin-crossover metal ions and radical ligands is proposed from a model Hamiltonian first restricted to exchange interactions. Unusual spin states structures emerge from the linkage of a singlet/triplet commutable metal centre with two doublet-radical ligands. The ground state nature is modulated by charge transfers and can exhibit a mixture of triplet and singlet local metal spin states. Besides, the superposition reaches a maximum for 2K M ¼ K 1 þ K 2 , suggesting a necessary competition between the intramolecular K M and inter-metal-ligand K 1 and K 2 direct exchange interactions. The results promote spinmerism, an original manifestation of quantum entanglement between the spin states of a metal centre and radical ligands. The study provides insights into spin-coupled compounds and inspiration for the development of molecular spin-qubits.

Modifications of Tanabe-Sugano d6 Diagram Induced by Radical Ligand Field: Ab Initio Inspection of a Fe(II)-Verdazyl Molecular Complex

“…As recently reported, the entanglement between local spin states is directly controlled by the relative amplitudes of the direct exchange values and conditions which might not be fulfilled in the examined compound 1. 21…”

“…One should stress that the local S Fe = 1 spin state involves a single pair of LMOs, a manifestation of the absence of orbital degeneracy as schematically shown in Scheme . The local spin values can result either from pure spin states or superpositions of different spin multiplicities as manifested in spinmerism. , Therefore, four different classes can be a priori anticipated in the energy spectrum of 1 .…”

“…However, the absence of a mixed-spin state on the metal in a S L = 1 ligand field is more puzzling at first. As recently reported, the entanglement between local spin states is directly controlled by the relative amplitudes of the direct exchange values and conditions which might not be fulfilled in the examined compound 1 …”

“…More recently, transition metal ions combined with organic ligands have been considered as possible targets in the development of molecular-based quantum units of information, for example, qubits or qudits (see for example refs − ). Theoretical studies have also revealed the potential interest of radical ligands for the manipulation of quantum information via the entanglement of local spin degrees of freedom. , A prerequisite is the binding of radical ligands to paramagnetic metal centers without losing their open-shell character. In this respect, oxoverdazyl-based ligands have proven to fulfill such requirements, giving rise to a wealth ofmagnetic coupling schemes. − Furthermore, the ease with which chemical modifications can be made and the well-established redox activity of organic-based compounds make such materials particularly interesting.…”

“…Theoretical studies have also revealed the potential interest of radical ligands for the manipulation of quantum information via the entanglement of local spin degrees of freedom. 20,21 A prerequisite is the binding of radical ligands to paramagnetic metal centers without losing their open-shell character. In this respect, oxoverdazyl-based ligands have proven to fulfill such requirements, giving rise to a wealth ofmagnetic coupling schemes.…”