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OptoElectronics and Communications Conference and International Conference on Photonics in Switching and Computing (OECC/PSC)

Integrated Beam Steering Using a 2D Focusing Grating Coupler for Scalable Trapped Ion Quantum Computing

Mizuki Shirao, Daniel Klawson, Sara Mouradian, Ming C. Wu

Published Jul 3, 2022• 1 citation
Publisher

Abstract

A scalable beam steering device is proposed for control of ion trap quantum computers. A combination of a waveguide array and a two-dimensional focusing grating coupler is used to generate 8xN beam spots at 729 nm wavelength in free space.
DOI
10.23919/oecc/psc53152.2022.9849897

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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 68 μm above the chip. Simulations show that the couplers achieve a diffraction-limited spot with a 4.3 μm beam waist along the trap axis and 2.2 μm perpendicular to the trap axis. Controlled interference of the TE 00 and TE 10 modes results in crosstalk of –20 dB to –30 dB at ion separations of 5–8 μm 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.
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.
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.