Purcell-enhanced emission of erbium ions in nanocrystals using a tunable Fabry-Perot resonator

Rare-earth spin qubits have gained attention as a promising quantum sensing platform due to their narrow energy level transitions, long optical spin coherence lifetimes, and on-chip integrability. However, the lifetime of spin coherencies suffers from interactions between the qubits and noisy environments. Resonant cavities have been used to enhance spin-photon interactions. Here, we demonstrate an active resonant cavity platform to introduce a Purcell-enhanced emission of erbium ions doped in yttrium orthosilicate and oxychlorides nanocrystals. Erbium ion-doped nanocrystals are located on the cavity utilizing a thin film of vanadium dioxide on a gold back-mirror and sapphire substrate, which acts as a tunable Fabry-Perot resonator for the erbium atomic level transitions near the telecom wavelength of 1550 nm. Vanadium dioxide is an active material whose optical properties change dramatically at a metal-insulator phase transition, lending control over the cavity mode. We observe an enhanced fluorescence lifetime and spin relaxation rate of an ensemble of erbium ions at a telecom wavelength of 1536 nm at low temperature with an external magnetic field, which induces a 3-level energy system. Such reconfigurable cavity platforms benefit the development of on-chip quantum devices.