Spin-Phonon Relaxation and Decoherence in a Three-Dimensional Paired-Ion Framework Composed of Vanadyl Porphyrin Qubits

Molecular electron spin qubits are an emerging platform for quantum technologies due to their atomic-scale synthetic tunability. Supramolecular structures can also place these qubits at precise positions within ordered arrays, allowing the scale-up of qubit architectures through a bottom-up approach. Here, we introduce the first three-dimensional paired-ion framework (PIF), VO-3D-PIF-1, which is composed of a concentrated array of S = 1/2 vanadyl porphyrin spin qubits arranged by ionic lattice interactions. The PIF was characterized using electron paramagnetic resonance spectroscopy to demonstrate the impact of framework structure and spin density on spin–lattice relaxation (T1) and spin decoherence (Tm). The high vanadyl porphyrin spin density within the framework (0.125 spins/nm3) promotes dipolar-driven decoherence, with Tm = 200–400 ns over a temperature range of 140–5 K. Spin–lattice relaxation mirrors that of vanadyl porphyrins in dilute solution, suggesting that the weak ionic interactions assembling the porphyrins within the secondary coordination sphere do not adversely affect phonon-induced T1 relaxation.