Strategies for Accessing Spin Molecular Quantum Processors

The controlled integration of single or multi-qubit magnetic molecules into superconducting circuits is key for the development of hybrid quantum computing architectures, as a suitable strategy for exploiting spin-based molecular quantum processors. This avenue might show competitive advantages over other solid-state schemes in view of the possibilities afforded by chemical design, allowing among other things to embed non-trivial quantum functionalities within each molecule (<i>Nature Chem. </i><b>2019</b>, <i>11</i>, 301-309). We have shown that multinuclear complexes of lanthanide ions with inequivalent metal sites ([LnLn’] or [LnLn’Ln]) gather the conditions to behave as two- or three-qubit quantum gates (<i>J. Am. Chem. Soc. </i><b>2014</b>, <i>136</i>, 14215-14222; <i>Chem. Sci. </i><b>2022</b>, <i>13</i>, 5574-5581), 64-spin qudits (<i>Commun. Chem. </i><b>2020</b>, <i>3</i>, 176) or to realize quantum error corrections (<i>Chem. Sci. </i><b>2020</b>, <i>11</i>, 10337-10343). We show here that a [Dy₂] analogue of this family fulfills the main requisites to act as a two-qubit quantum processor and show that the dynamic magnetic properties characteristic of this behaviour are preserved when transferred in form of a few molecules thick layers inside the 20 mm wide loops of a gradiometric micro-SQUID sensor (Figure, middle and right). These results indicate that it may be possible to address multi-qubit molecular spin processors with on-chip superconducting circuits without altering their relevant properties. The use of soft nanolithography techniques may open the way to achieve this goal in practice.