Circuit Quantum Electrodynamics Experiments with Molecular Spin Qudits

Scaling up quantum processors remains very challenging, even for today’s most successful platforms. Molecular complexes, synthesized by chemical methods, combine a perfect reproducibility with the ability to tune their properties. The latter property allows scaling up quantum resources within each molecule, e.g. by encoding multiple qubits or, in general, d-dimensional qudits in their electronic and nuclear spin states. A molecule can then can act as a small-scale universal quantum processor or even correct errors [1-4]. Exploiting these systems calls for a solid-state platform able to initialize, control and read-out the molecular spins, and of establishing the communication channels between remote spins that are needed for full scalability [5]. I’ll discuss recent experiments aimed at achieving this goal by coupling molecular spins to chips hosting multiple LC superconducting resonators and transmission lines [6-8]. Results performed on molecular spin ensembles provide proof-of-concept implementations of the basic quantum operations. Also, we find that the circuit can mediate effective interactions between distinct spin ensembles located on separately addressable remote resonators. In the case of electronuclear spin qudits, high cooperativity coupling to electronic and even nuclear spins has been achieved [6], which provide the basis for a full control and detection of the multiple spin states. Finally, I’ll discuss different strategies, based on the optimization of either the circuit [7,9] or the molecular integration [10], for extending this approach to address individual molecular spins.