Electronic spins in different environments are currently investigated as potential qubits, i.e. the logic units of quantum computers. These have to retain memory of their quantum state for a sufficiently long time (phase memory time, T_m) allowing quantum operations to be performed. For molecular based spin qubits, strategies to increase phase coherence by removing nuclear spins are rather well developed, but it is now crucial to address the problem of the rapid increase of the spin–lattice relaxation rate, T₁ ⁻¹, with increasing temperature that hampers their use at room-temperature. Herein, thanks to the combination of pulsed EPR spectroscopy and AC susceptometry we evidence that an evaporable vanadyl complex of formula VO(dpm)₂, where dpm⁻ is the anion of dipivaloylmethane, presents a combination of very promising features for potential application as molecular spin-qubit. The spin–lattice relaxation time, T₁, studied in detail through AC susceptometry, decreases slowly with increasing temperature and, more surprisingly, it is not accelerated by the application of an external field up to several Teslas. State-of-the art phase memory times for molecular spin systems in protiated environment are detected by pulsed EPR also in moderate dilution, with values of 2.7 μs at 5 K and 2.1 μs at 80 K. Low temperature scanning tunnel microscopy and X-ray photoelectron spectroscopy in situ investigations reveal that intact molecules sublimated in ultra-high vacuum spontaneously form an ordered monolayer on Au(111), opening the perspective of electric access to the quantum memory of ensembles of spin qubits that can be scaled down to the single molecule.

Vanadyl phthalocyanine (VOPc) contains a highly coherent spin S = ½, which is of interest for applications in quantum information. Preservation of long coherence times upon deposition on conductive materials is crucial for use of single-spin in devices. Here, we report a detailed investigation of the structural, electronic and magnetic properties of a hybrid architecture constituted by a monolayer film of VOPc molecules deposited on graphene/SiC(0001). Graphene (Gr) is a two-dimensional conductor with exceptional chemical stability, a property which we exploited here to preserve the spin of VOPc. Low temperature-scanning tunneling microscopy supported by density functional theory (DFT) simulations revealed that VOPc molecules were adsorbed intact on the Gr/SiC(0001) surface in a planar geometry assuming a unique configuration in which the vanadyl group is projected out toward the vacuum, different to that found commonly on other conductive surfaces. Furthermore, X-ray photoelectron spectroscopy and UV-photoelectron spectroscopy (flanked theoretically by DFT) showed that VOPc interact weakly with the Gr/SiC(0001) substrate to preserve its electronic configuration with the unpaired electron located on the V ion. These findings were confirmed by X-ray magnetic circular dichroism, revealing that the S = ½ character of the VOPc assembly on Gr/SiC(0001) was preserved, in agreement with the theoretical prediction. Hence, molecules could be adsorbed and used as qubits on substrates of technological importance, such as graphene. This new hybrid architecture could be employed for local investigation of static and dynamic spin properties and as molecular qubits for spintronic applications.

Subtle isotopic effects on spin dynamics are captured using Muon Spin Relaxation experiments on isotopically enriched Dy-based single molecule magnets.