Unparalleled selectivity and electronic structure of heterometallic [LnLn'Ln] molecules as 3-qubit quantum gates

Heterometallic lanthanide [LnLn′] coordination complexes that are accessible thermodynamically are very scarce because the metals of this series have very similar chemical behaviour. Trinuclear systems of this category have not been reported. A coordination chemistry scaffold has been shown to produce molecules of type [LnLn′Ln] of high purity, i.e. exhibiting high metal distribution ability, based on their differences in ionic radius. Through a detailed analysis of density functional theory (DFT) based calculations, we discern the energy contributions that lead to the unparalleled chemical selectivity of this molecular system. Some of the previously reported examples are compared here with the newly prepared member of this exotic list, [Er2Pr(LA)2(LB)2(py)(H2O)2](NO3) (1) (H2LA and H2LB are two β-diketone ligands). A magnetic analysis extracted from magnetization and calorimetry determinations identifies the necessary attributes for it to act as an addressable, conditional multiqubit spin-based quantum gate. Complementary ab initio calculations confirm the feasibility of these complexes as composite quantum gates, since they present well-isolated ground states with highly anisotropic and distinct g-tensors. The electronic structure of 1 has also been analyzed by EPR. Pulsed experiments have allowed the establishment of the quantum coherence of the transitions within the relevant spin states, as well as the feasibility of a coherent control of these states via nutation experiments.
The authors thank the European Union's Horizon 2020 research and innovation programmes QUANTERA project SUMO and FET-OPEN grant 862893 FATMOLS (GA and OR) the Spanish AEI for grants PGC2018-098630-B-I00 (GA and DA), PID2020-118329RB-I00 (OR), PID2020-112806RB-I00 (DGR and CB) and the Severo Ochoa Excellence Accreditation 2020–2023 CEX2019-000925-S (DGR and CB), the ICIQ foundation (DGR and CB) and the Generalitat de Catalunya for a Beatriu de Pinós fellowship (2019-BP-00015, DR), an FI grant (also financed by AGAUR and the European Social Fund, DGR) an FI-SDUR Grant (2020-FISDU-00492, DM), the CERCA program and the ICREA Academia 2018 Prize (GA), as well as the National EPR Facility at the University of Manchester for support with the EPR measurements. This work used resources of the ALBA synchrotron through access to beamline 13-XALOC.