Surface-trap integrated vertical Fabry–Perot microcavity for fast trapped ion networks

Remote entanglement generation rate is the current bottleneck in realizing a scalable distributed quantum computer with trapped ions. Utilizing ion-cavity interaction with a micro Fabry-Perot cavity promises a two-order-of-magnitude enhancement of the remote entanglement generation rate. However, due to the mechanical stability of the cavity and the accurate localization of the ion at a cavity antinode in the presence of a dielectric cavity mirror surface, photon collection within the cavity is currently slower than free-space photon collection with a high numerical aperture lens [1]. In this work, we designed and optically characterized a surface-trap-integrated vertical Fabry-Perot cavity package, enabling stable microcavity alignment via flexure-based optomechanics, precise ion localization, and multi-ion compatibility. We measured 67\% cavity-to-fiber coupling efficiency with <83 ppm non-transmission loss, corresponding to an expected cooperativity of 2.19(4) with 100 ppm and 1400 ppm transmission coating, and a photon extraction probability to single-mode fiber of 35(1)\%. This efficiency allows for an improved success probability of $10^{-2}$ with an improved repetition rate of $2.7~\textrm{MHz}$ that gives a remote entanglement generation rate of \(2.7\times10^{4}~\mathrm{s^{-1}}\) under polarization encoding, which is in line with the speed of local two-qubit gates.

[1] J. O’Reilly, G. Toh, I. Goetting, S. Saha, M. Shalaev, A. L. Carter, A. Risinger, A. Kalakuntla, T. Li, A. Verma, and C. Monroe. Fast photon-mediated entanglement of continuously cooled trapped ions for quantum networking. Physical Review Letters, 133(9), Aug. 2024.