Micro-cavity-integrated surface electrode chip for enhanced photon collection in trapped ion quantum computers

Achieving high photon collection efficiency from a single trapped ion is essential for implementing fast remote entangling gates, a critical component in developing large-scale trapped ion quantum computers [1]. The use of micro Fabry-Perot cavities stands out as a promising technique to enhance this efficiency, and many works have been done to implement micro cavities with trapped ion systems [2-3]. Our poster presentation describes design optimization, fabrication, and characterization methods for an integrated surface electrode chip trap with microcavity and fiber coupling optics.



The integrated system comprises a surface electrode chip, concave micromirror, flexure mount, and integrated optics for fiber coupling. First, we designed and fabricated the surface electrode chip trap with a circular flat mirror optimized for trapping ¹³⁸Ba⁺ ions. For microcavity design, we employed Fox-Li simulations and calculated photon collection efficiency based on cavity quantum electrodynamics principles. Subsequently, the micromirror was fabricated with a CO₂ laser ablation on a fused silica substrate and characterized using a white light interferometer and atomic force microscopy [4]. To achieve stable cavity length locking, we designed and characterized a custom flexure mount, subsequently implementing Pound-Drever-Hall locking. Finally, we developed chip-integrated optics to couple the fiber and the microcavity modes.



This comprehensive approach to integrating microcavities into surface electrode chip traps is anticipated to improve photon collection efficiency significantly. The techniques presented contribute to the ongoing efforts to develop robust and scalable trapped ion quantum computing systems.

[1] C. Monroe, et al., Large-Scale Modular Quantum-Computer Architecture with Atomic Memory and Photonic Interconnects, Phys. Rev. A 89, (2014).

[2] S. Ritter, et al., An Elementary Quantum Network of Single Atoms in Optical Cavities, Nature 484, 195 (2012).

[3] T. Kim, P. Maunz, and J. Kim, Efficient Collection of Single Photons Emitted from a Trapped Ion into a Single-Mode Fiber for Scalable Quantum-Information Processing, Phys. Rev. A 84, (2011).

[4] D. Hunger, et al., Laser Micro-Fabrication of Concave, Low-Roughness Features in Silica, AIP Advances 2, (2012).