Metal–ligand covalency enables room temperature molecular qubit candidates

Abstract

Metal–ligand covalency enables observation of coherent spin dynamics to room temperature in a series of vanadium(iv) and copper(ii) catechol complexes.

The dynamic ligand field of a molecular qubit: decoherence through spin–phonon coupling

“…This has inspired resent research efforts to better understand the nature of spin-phonon coupling in transition metal complexes and how it might be tuned and controlled by variations in the ligand set and thus the ligand field environment. [13][14][15]33,44 As highlighted in the Introduction, spin-phonon couplings also play important roles in single molecule magnets and photophysics, and studies directed at fundamental understanding will have broad impact.…”

“…Thus, the parent vibrational modes provide a means to make quantitative comparisons across Cu(II) and V(IV) complexes. The experimental and calculated g-values of Cu(II) qubits are given in Table 1, 14,33,72,73 while spin-phonon linear coupling terms and additional computational results are given in Table 5. Note X-ray crystal structures were utilized for [Cu(mnt)2] 2-, [Cu(bdt)2] 2-, and [Cu(bds)2] 2-(bds = benzene-1,2-diselenate) complexes, as their structures were not well reproduced using DFT geometry optimization.…”

“…For example, vanadyl phthalocyanine (VOPc) diluted in a diamagnetic titanyl matrix exhibits room temperature coherence with a Tm of ~1 s at 300 K, even in the presence of a nuclear spin containing environment. 37 Spin echoes have also been observed up to room temperature in the benzene-1,2-dithiolate (bdt) ligated (Ph4P)2[Cu(C6H4S2)2] 33 (Cu(bdt)2) and the maleonitriledithiolate (mnt) ligated (Ph4P)2[Cu(mnt)2] 50 (Cu(mnt)2) complexes diluted in diamagnetic Ni lattices. At lower temperatures (~< 80 K), relaxation is dominated by the direct, Raman, and Orbach mechanisms, while a mechanism involving spin-phonon coupling and the modulation of the energy gap between the Ms = ± ½ sublevels dominates at higher temperatures.…”

“…28 In these nuclear spin-free environments, T1 has proved to be the upper bound to coherence lifetimes, which further motivates efforts to better understand contributions to T1, including the role of the geometric and electronic structure of the transition metal complex. [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.…”

“…Comparisons between 1) and 2) and six coordinate, pseudo Oh V(IV) complexes have also been made to highlight structural and electronic contributions to T1. 13,33,53 As shown below, multiple contributions need to be accounted for in order to make direct comparisons between S = ½ molecular qubits and thus to understand the origins of their coherence times.…”