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Optics Express

Focusing grating coupler for the generation of quantum sensors

Timur Abbasov, Sergey Zibrov, Ivan Stolyarov, Nikolay Orlikovskiy, Aidar R. Gabidullin, Sergey Arkhipov, Anton Shishkin, Vladimir Zheltikov, Alexey Denisov, I. Sherstov

Published Apr 23, 2025• 2 citations
Publisher

Abstract

We report the development and experimental testing of focusing grating couplers (FGCs) designed for integration with surface ion traps, aiming to advance compact ion-based technologies for next-generation quantum sensors to be used in ion frequency standards, gravimetry, and quantum computing. Through analytical calculations, we optimized the simulation and fabrication processes. Using numerical simulations, we further optimized the focusing configuration of the grating couplers to achieve a focal point approximately 210 µm above the chip surface. The fabricated focusing couplers were experimentally tested and confirmed to effectively focus laser radiation at a height of 200-210 µm above the chip surface.

DOI
10.1364/oe.558926

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We report the development and experimental testing of focusing grating couplers (FGCs) designed for integration with surface ion traps, aiming to advance compact ion-based technologies for next-generation quantum sensors to be used in ion frequency standards, gravimetry, and quantum computing. Through analytical calculations, we optimized the simulation and fabrication processes. Using numerical simulations, we further optimized the focusing configuration of the grating couplers to achieve a focal point approximately 210 µm above the chip surface. The fabricated focusing couplers were experimentally tested and confirmed to effectively focus laser radiation at a height of 200-210 µm above the chip surface.
Monolithic integration of control technologies for atomic systems presents a promising route to the development of quantum computers and portable quantum sensors. Trapped atomic ions form the basis of high-fidelity quantum information processors and high-accuracy optical clocks, but currently rely on free-space optics for ion control, limiting portability and scalability. Here we demonstrate a surface-electrode ion trap which delivers all wavelengths required for ionization, cooling, coherent operations, and quantum-state preparation and detection of Sr+^{+}+ qubits using integrated waveguides and grating couplers. Laser light from the violet to the infrared is coupled onto the chip via an optical-fiber array, creating an inherently stable optical path that we use to demonstrate qubit coherence resilient to platform vibrations. This demonstration of CMOS-compatible integrated-photonic surface-trap fabrication, robust packaging, and enhanced qubit coherence represents a key advance in the development of portable trapped-ion quantum sensors and clocks, and it lights the way toward the complete, individual control of larger numbers of ions in quantum information processing systems.
Abstract Monolithic integration of control technologies for atomic systems is a promising route to the development of quantum computers and portable quantum sensors1–4. Trapped atomic ions form the basis of high-fidelity quantum information processors5, 6 and high-accuracy optical clocks7. However, current implementations rely on free-space optics for ion control, which limits their portability and scalability. Here we demonstrate a surface-electrode ion-trap chip8, 9 using integrated waveguides and grating couplers, which delivers all the wavelengths of light required for ionization, cooling, coherent operations and quantum state preparation and detection of Sr+ qubits. Laser light from violet to infrared is coupled onto the chip via an optical-fibre array, creating an inherently stable optical path, which we use to demonstrate qubit coherence that is resilient to platform vibrations. This demonstration of CMOS-compatible integrated photonic surface-trap fabrication, robust packaging and enhanced qubit coherence is a key advance in the development of portable trapped-ion quantum sensors and clocks, providing a way towards the complete, individual control of larger numbers of ions in quantum information processing systems.
Trapped-ion quantum computing requires precise optical control for individual qubit manipulation. However, conventional free-space optics face challenges in alignment stability and scalability as the number of qubits increases. Integrated photonics offers a promising alternative, providing miniaturized optical systems on a chip. Here, we propose a design for a multimode photonic circuit integrated with a surface-electrode ion trap capable of targeted and reconfigurable light delivery. Three closely positioned ions can be addressed using a focusing grating coupler that emits multimode light through electrode openings to ions trapped 80 μμμm above the chip. Simulations show that the couplers achieve diffraction-limited spot with a 4.3 μμμm beam waist along the trap axis and 2.2 μμμm perpendicular to the trap axis. Controlled interference of the TE10_{\text{10}}10​ and TE20_{\text{20}}20​ modes results in crosstalk of -20 dB to -30 dB at ion separations of 5-8 μμμm when addressing ions individually, and down to -60 dB when two of the three ions are addressed simultaneously. Additionally, the higher-order TE modes can offer a novel mechanism for driving spin-motion coupling transitions, potentially enabling alternative approaches to quantum gates and simulations. The proposed integrated platform offers a viable path for constructing large-scale trapped-ion systems, leveraging the benefits of nanophotonic design for precise and reliable ion manipulation.