A high-resolution molecular spin-photon interface at telecommunication wavelengths.

Optically addressable electronic spins in polyatomic molecules are a promising platform for quantum information science, with the potential to enable scalable qubit design and integration through atomistic tunability and nanoscale localization. However, optical state- and site-selection are an open challenge. In this work, we introduce an organo-erbium spin qubit in which narrow (megahertz-scale) optical and spin transitions couple to provide high-resolution access to spin degrees of freedom with telecommunication-frequency light. This spin-photon interface enables demonstration of optical spin polarization and readout that distinguishes between spin states and magnetically inequivalent sites in a molecular crystal. Operation at frequencies compatible with mature photonic and microwave devices provides an opportunity for engineering scalable, integrated molecular spin-optical quantum technologies. Editor's summary: There are several qubit platforms being explored for applications in quantum technologies. For quantum communication applications, one of the most desirable properties would be operation at telecommunication wavelengths. Weiss et al. have introduced a spin qubit based on an engineered organo-erbium molecule platform. They demonstrated addressability of the spin of the molecule with light at telecommunication wavelengths and verified the quantum behavior. This synthetic molecular approach to designing qubits is promising for achieving targeted performance for required applications. —Ian S. Osborne [ABSTRACT FROM AUTHOR]