Ligand Radicals as Modular Organic Electron Spin Qubits

Abstract

The intrinsic redox activity of the dithiolene ligand is presented here as the novel spin host in the design of a prototype molecular electron spin qubit, where the traditional roles of the metal and ligand components in coordination complexes are inverted. A series of paramagnetic bis(dithiolene) complexes with group 10 metals—nickel, palladium, platinum—provides a backdrop to investigate the spin dynamics of the organic ligand radical using pulsed EPR spectroscopy. The temperature dependence of the phase memory time (TM) is shown to be dependent on the identity of the diamagnetic metal ion, with the short times recorded for platinum a consequence of a diminishing spin‐lattice (T1) relaxation time driven by spin‐orbit coupling. The utility of the radical ligand spin center is confirmed when it delivers one of the longest phase memory times ever recorded for a molecular two‐qubit prototype.

Enabling single qubit addressability in a molecular semiconductor comprising gold-supported organic radicals

“…This ratio was inverted for the Cl 3 CCN and CS 2 glassing mixtures in combination with CCl 4 . In contrast to the recent study of isoelectronic complexes, [PPh 4 ][M(adt) 2 ] (M = Ni, Pd, Pt) in CD 2 Cl 2 /DMF- d 7 ,20 here the only protons and methyl groups are those on the periphery of the dithiolene ligand (Fig. 1a).…”

“…2). 21,27,33,34,37 The splitting pattern ( g y > g x > g e > g z ) is the same as observed for isoelectronic bis(dithiolene) monoanions of group 10 metals given an identical 2 B 2g ground state ( vide infra ) 20,22. The spectrum exhibits a remarkable hyperfine splitting from the 197 Au nucleus ( I = 3/2, 100% abundant), where the quartet splitting of each principal g -value manifests with an unusual spacing and intensity distribution of the hyperfine lines.…”

“…The significance of SOC has been previously shown to impact on spin-lattice times when comparing first- and second-row metals in systems where the metal is the spin host 42. We recently revealed for this system where the ligand is the spin host anchored by the metal ion, that the latter represents a heavy-atom effect 20. The phenomenon is particularly pervasive in this qubit design, and we have begun to explore alternative uses for these molecules to replace dichalcogenides in graphene-based heterostructures 43…”

“…We proposed a new architecture of molecule-based spin qubits where the traditional role of the organic and inorganic components was inverted with spins residing on radical ligands and linked by diamagnetic metal ions. This was realized for a series of bis(dithiolene) complexes of group 10 metal ions of the formula [M(adt) 2 ] 1– (M = Ni, Pd, Pt; adt 2– = bis( p -anisyl)-1,2-ethenedithiolate) 20. The concept was expanded to a two-qubit species, [{Ni(adt)} 2 (μ-tpbz)] 2+ (tbpz = 1,2,4,5-tetrakis(diphenylphosphino)benzene), where the terminal ligands are electrochemically oxidized to their dithiolene radical form.…”

The Dynamic Ligand Field of a Molecular Qubit: Decoherence Through Spin–Phonon Coupling

“…[28][29][30][31][32][33][34][35][36][37][38][39][40][41][42][43][44] Recent works in this area by Sessoli et al 13,44 , Coronado et al 14,15 , and Freedman et al 33 have highlighted specific ligand field contributions to spin-phonon coupling and coherence dynamics. Additionally, T1 relaxation times will also play a major role when molecular qubits are entangled in dimers, [45][46][47][48][49] higher order complexes, or spin-dense arrays, 36 which will be required for the realization of quantum computing applications.…”