Scaling Up Electronic Spin Qubits into a Three-Dimensional Metal–Organic Framework

Abstract

Practical implementation of highly coherent molecular spin qubits for challenging technological applications, such as quantum information processing or quantum sensing, requires precise organization of electronic qubit molecular components into extended frameworks. Realization of spatial control over qubit-qubit distances can be achieved by coordination chemistry approaches through an appropriate choice of the molecular building blocks. However, translating single qubit molecular building units into extended arrays does not guarantee a priori retention of long quantum coherence and spin-lattice relaxation times due to the introduced modifications over qubit-qubit reciprocal distances and molecular crystal lattice phonon structure. In this work, we report the preparation of a three-dimensional (3D) metal-organic framework (MOF) based on vanadyl qubits, [VO(TCPP-Zn-bpy)] (TCPP = tetracarboxylphenylporphyrinate; bpy = 4,4'-bipyridyl) (1), and the investigation of how such structural modifications influence qubits' performances. This has been done through a multitechnique approach where the structure and properties of a representative molecular building block of formula [VO(TPP)] (TPP = tetraphenylporphyrinate) (2) have been compared with those of the 3D MOF 1. Pulsed electron paramagnetic resonance measurements on magnetically diluted samples in titanyl isostructural analogues revealed that coherence times are retained almost unchanged for 1 with respect to 2 up to room temperature, while the temperature dependence of the spin-lattice relaxation time revealed insights into the role of low-energy vibrations, detected through terahertz spectroscopy, on the spin dynamics.

First-Principles Investigation of Spin–Phonon Coupling in Vanadium-Based Molecular Spin Quantum Bits

“…These extrinsic factors can be tuned following two possible strategies: by stiffening the metal-ligand bonds and by tayloring supramolecular structures where the intra-molecular contribution to the normal modes is reduced and the phononic structure is modified and shifted at higher frequencies. [56] In conclusion, the results of our comparative first principles investigation open new pathways for the rational design of molecular qubits based on the combination of the coordination geometry and ligang field with crystal engineering.…”

The Dynamic Ligand Field of a Molecular Qubit: Decoherence Through Spin–Phonon Coupling

“…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.…”

Structural Dynamics of An ELM-11 Framework Transformation Accompanied with Double-Step CO2 Gate sorption: An NMR Spin Relaxation Study

“…Recently, the nuclear spin-lattice relaxation rates in paramagnetic substances have attracted much attention due to interest in distance-geometry [32], MRI-relaxation-agents [33], and quantum-computation [34] applications. The molecular motions, phase transitions, and inter-spin interactions in paramagnetic materials have been discussed through 1 H spin-lattice relaxation times (T 1 ) [35][36][37][38].…”