Abstract
The selection of molecular spin qubits with a long coherence time, Tm, is a central task for implementing molecule-based quantum technologies. Even if a sufficiently long Tm can be achieved through an efficient synthetic strategy and ad hoc experimental measurement procedures, many factors contributing to the loss of coherence still need to be thoroughly investigated and understood. Vibrational properties and nuclear spins of hydrogens are two of them. The former plays a paramount role, but a detailed theoretical investigation aimed at studying their effects on the spin dynamics of molecular complexes such as the benchmark phthalocyanine (Pc) is still missing, whereas the effect of the latter deserves to be examined in detail for such a class of compounds. In this work, we adopted a combined theoretical and experimental approach to investigate the relaxation properties of classical [Cu(Pc)] and a CuII complex based on the ligand tetrakis(thiadiazole)porphyrazine (H2TTDPz), characterized by a hydrogen-free molecular structure. Systematic calculations of molecular vibrations exemplify the effect of normal modes on the spin–lattice relaxation process, unveiling a different contribution to T1 depending on the symmetry of normal modes. Moreover, we observed that an appreciable Tm enhancement could be achieved by removing hydrogens from the ligand.
Highlights
Quantum bits, or qubits, represent the fundamental units for the realization of quantum computers
Our investigations conducted with pulsed EPR spectroscopy verified that both T1 and Tm follow different temperature dependences when the magnetic dilution is pushed below the 1% limit
We proved experimentally that a coherence time enhancement of porphyrazine-based complexes might be achieved by replacing peripheral hydrogen atoms of [Cu(Pc)] with thiadiazole units of [Cu(TTDPz)], partially highlighting that hydrogen atoms placed around the 6 Å spin diffusion barrier affect the coherence time of the central ion.[38,40]
Summary
Qubits, represent the fundamental units for the realization of quantum computers. The spectra obtained for 220%, and 20.1% are interpreted and simulated along the same lines In this case, simulations were implemented by adopting a set of parameters reported in the literature (Figure S8).[56] Compounds 12% and 10.1% were characterized via CW-EPR and echo detected field swept (EDFS) spectroscopy at the Q-band (υ ≈ 34 GHz). Atomistic simulation techniques were applied to copper complexes to catch how the structural differences between the molecular systems affect the composition of the normal modes of vibration Their influence on the spin state can be estimated through the SPC coefficients. The first coordination sphere is strongly perturbed only by gerade modes
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