Coherent Spin Manipulation in Mononuclear Gadolinium-Substituted Polyoxometalate–Organic Hybrids

Abstract

While most research on molecule-based electron spin qubits has focused on S = 1/2 ions for single-qubit gates, the need for qubit interactions in quantum operations has driven interest in higher-spin molecules and multilevel states. Herein, we study the spin dynamics of two mononuclear gadolinium-substituted polyoxometalate-organic hybrids with the general formula K₅[Gd(α-XW₁₁O₃₉)(H₂L)]·14H₂O (X = Si, Ge; H₂L = N,N′-dimethyl-N,N′-bis(2-hydroxy-3-formyl-5-bromobenzyl)ethylenediamine), 1_Si-Gd and 1_Ge-Gd. Pulsed EPR measurements reveal spin–lattice relaxation (T₁) and quantum coherence (T_m) times of up to 2315 and 2.6 μs at 3 K, respectively, for diamagnetically diluted samples, as well as Rabi oscillations up to 20 K. The obtained results make 1_Si-Gd and 1_Ge-Gd two of the few Gd-based complexes displaying such behavior, highlighting the challenge of coherently manipulating the spin states of Gd. Moreover, their hybrid organic–inorganic nature endows them with chemical robustness and solution stability, essential prerequisites for surface immobilization and future integration in practical devices.