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Distributed quantum computing with trapped ions is expected to rely on modular architectures in which many small ion registers are connected by photonic links [1]. In such a network, efficient ion–cavity coupling is crucial because it increases photon collection into a well-defined cavity mode and fiber channel, thereby boosting the remote-entanglement rate between modules. Short fiber Fabry–Perot cavities (FFPCs) are a promising route to this regime, but bringing dielectric mirrors close to the ion can introduce stray charging, trap distortion, and excess heating [2].
We present a combined hardware and fabrication approach toward compact, shielded ion–cavity interfaces for a linear ion trap. First, we developed a miniaturized, monolithic linear Paul trap for transverse FFPC integration, fabricated from gold-coated fused silica via selective laser etching [3]. The monolithic geometry removes post-fabrication electrode alignment, preserves trap symmetry, and provides large optical access while allowing conductive shielding of nearby cavity holders. Single 40Ca+ ions were successfully trapped, and the measured secular frequencies agree with finite-element simulations, yielding fitted imperfection factors of 0.96, 0.95, and 0.92 for the two radial and axial modes, respectively.
Second, we developed an adaptive CO2-laser machining method for fiber mirrors with in situ interferometric imaging [4]. The method updates multi-shot ablation patterns from the measured surface after each step. A key control parameter is the pause between shots, which tunes heat accumulation and therefore the lateral extent of each ablation event, enabling a controlled transition between global shaping and local correction. Using this approach, we fabricate Gaussian or near-spherical concave mirrors with radii of curvature of 250-700 µm, effective diameters of about 60 µm, and low ellipticity ($r_e < 0.2$) with close-to-unity yield. After high-reflectivity coating, the resulting FFPCs reach a finesse of $1.5 × 10^5$ at 854 nm and maintain $>10^5$ for cavity lengths up to 430 µm. These results provide key components for scalable, low-loss ion–photon interfaces in distributed trapped-ion quantum computing.
References
- C. Monroe, R. Raussendorf, A. Ruthven, K. R. Brown, P. Maunz, L.-M. Duan, and J. Kim, Large-scale modular quantum-computer architecture with atomic memory and photonic interconnects, Phys. Rev. A 89, 022317 (2014).
- H. Takahashi, E. Kassa, C. Christoforou, and M. Keller, Strong coupling of a single ion to an optical cavity, Phys. Rev. Lett. 124, 013602 (2020).
- S. Teh, E. Kassa, S. Gao, S. Oya, and H. Takahashi, Ion Trapping with a Laser-written 3D Miniaturized Monolithic Linear Paul Trap for Microcavity Integration, arXiv:2409.05075 (2024).
- S. Gao, V. Kavungal, S. Oya, D. Okuno, E. Kassa, W. J. Hughes, P. Horak, and H. Takahashi, Profile control of fiber-based micro-mirrors using adaptive laser shooting with in situ imaging, Opt. Express 33, 39009 (2025).
| Academic level | PhD student |
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