Abstract
Molecular electronic spins are good candidates as qubits since they are characterized by a large tunability of their electronic and magnetic properties through a rational chemical design. Coordination compounds of light transition metals are promising systems for spin-based quantum information technologies, thanks to their long spin coherence times up to room temperature. Our work aims at presenting an in-depth study on how the spin–phonon coupling in vanadyl-acetylacetonate, [VO(acac)2], can change as a function of temperature using terahertz time-domain spectroscopy and density functional theory (DFT) calculations. Powder THz spectra were recorded between 10 and 300 K. The temperature dependence of vibrational frequencies was then accounted for in the periodic DFT calculations using unit-cell parameters measured at two different temperatures and the optimized ones, as usually reported in the literature. In this way, it was possible to calculate the observed THz anharmonic frequency shift with high accuracy. The overall differences in the spin–phonon coupling magnitudes as a function of temperature were also highlighted showing that the computed trends have to be ascribed to the anisotropic variation of cell parameters.
Highlights
The quantum bit or qubit[1] is the basic element of quantum information theory (QIT);[2] it differs from its classical equivalent, the bit, since it can exploit the quantum superposition of the two states 0 and 1
The two spectra are identical, except for the intensity that is related to the different concentrations of vanadyl-acetylacetonate in the samples
The harmonic approximation of molecular vibrations is highly valuable for interpretation of the main features of the vibrational spectra but it cannot explain all their fine structures, which depend on the temperature
Summary
The quantum bit or qubit[1] is the basic element of quantum information theory (QIT);[2] it differs from its classical equivalent, the bit, since it can exploit the quantum superposition of the two states 0 and 1. Coordination compounds of light transition metals, such as Ti(III), V(IV), and Cu(II),[10−12] have demonstrated to be promising systems at least from the point of view of the superposition state’s lifetime. This quantity is determined by the spin−spin relaxation time, T2, but it is usually quantified through the phase memory time, Tm, that is the measurable lower limit of T2.13 Another fundamental parameter in the evaluation of the qubit performance is the spin−lattice relaxation time, T1.14 If it is too short, it limits Tm,[11] preventing the implementation of more complex algorithms. In solid-state qubits, T1 is closely connected with lattice vibrations, i.e., phonons. Vibrations perturb spin degrees of freedom through the modulation of orbital contributions and the presence of spin−orbit coupling
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