Erbium complexes as optically addressable molecular spin qubits

Optically addressable molecular spin qubits have emerged as a promising platform to explore spin-light interactions at the nanoscale within low-dimensional, chemically synthesized material systems. Recent work has called particular attention to the use of molecular lanthanide complexes – taking advantage of shielded optical transitions between 4f-orbital states to achieve exceptionally narrow linewidths. Working in this context, we present experimental progress on erbium-based optically addressable molecular spin qubits [1]. We demonstrate how narrow optical transitions result in full optical resolution of the ground- and excited-state spin sublevels - yielding a molecular spin-photon interface at telecommunication wavelengths. We further show that, at sub-kelvin temperatures, this spin-selective optical interface can be used to polarize and read out populations of the coherently controllable ground state spin.



[1] L.R. Weiss*, G.T. Smith*, R.A. Murphy*, et al., A high-resolution molecular spin-photon interface at telecommunication wavelengths. Science 390,76-81(2025).