Behavior of ⁴⁰Ca⁺ ions trapped near an optical fiber in a cryogenic surface-electrode trap for use in a quantum repeater

Quantum networking aims to establish entanglement over long distances as a resource for scalable quantum computing, secure communication, and enhanced sensing. Trapped ions offer distinct advantages as stationary qubits including their long coherence time, precise state preparation and control, and high-fidelity two-qubit gates. Telecom-wavelength photons are the flying qubit with lowest loss in fibers connecting repeater stations and network nodes. Optical loss at the ion-photon interface can significantly limit the entanglement rate between nodes. A high cooperativity optical cavity can increase collection efficiency. Small cavity lengths that enable strong coupling and efficient photon extraction under practical constraints also bring the ion and laser beams close to the dielectric surface of the cavity mirrors, which can lead to increased motional heating and sensitivity to stray charge accumulation. Here we characterize the behavior of a ⁴⁰Ca⁺ ion trapped in a cryogenic surface-electrode trap hundreds of microns from the tip of an optical fiber, mimicking the conditions near the mirror of a trap-integrated fiber Fabry-Perot cavity. We characterize stray fields and determine heating rates for various ion-fiber distances and address anticipated challenges for coherent control of ions interfacing with an integrated fiber-based optical cavity at cryogenic temperatures.