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arXiv:2401.18056 · Physical Review X

Multizone Trapped-Ion Qubit Control in an Integrated Photonics QCCD Device

Carmelo Mordini, Alfredo Ricci Vásquez, Yuto Motohashi, Mose Müller, Maciej Malinowski, Chi Zhang, Karan K. Mehta, Daniel Kienzler, Jonathan Home

Published Feb 24, 2025• 29 citations
arXivHTMLPDF

Abstract

Multiplexed operations and extended coherent control over multiple trapping sites are fundamental requirements for a trapped-ion processor in a large-scale architecture. Here, we demonstrate these building blocks using a surface-electrode trap with integrated photonic components which are scalable to larger numbers of zones. We implement a Ramsey sequence using the integrated light in two zones, separated by 375 μ m , performing transport of the ion from one zone to the other in 200 μ s between pulses. In order to achieve low motional excitation during transport, we develop techniques to measure and mitigate the effect of the exposed dielectric surfaces used to deliver the integrated light to the ion. We also demonstrate simultaneous control of two ions in separate zones with low optical crosstalk and use this to perform simultaneous spectroscopy to correlate field noise between the two sites. Our work demonstrates the first transport and coherent multizone operations in integrated photonic ion trap systems, forming the basis for further scaling in the trapped-ion quantum charge-coupled device architecture.

DOI
10.1103/physrevx.15.011040

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•Jan 14, 2020•4 citations
Multiplexed operations and extended coherent control over multiple trapping sites are fundamental requirements for a trapped-ion processor in a large-scale architecture. Here, we demonstrate these building blocks using a surface-electrode trap with integrated photonic components which are scalable to larger numbers of zones. We implement a Ramsey sequence using the integrated light in two zones, separated by 375 μ m , performing transport of the ion from one zone to the other in 200 μ s between pulses. In order to achieve low motional excitation during transport, we develop techniques to measure and mitigate the effect of the exposed dielectric surfaces used to deliver the integrated light to the ion. We also demonstrate simultaneous control of two ions in separate zones with low optical crosstalk and use this to perform simultaneous spectroscopy to correlate field noise between the two sites. Our work demonstrates the first transport and coherent multizone operations in integrated photonic ion trap systems, forming the basis for further scaling in the trapped-ion quantum charge-coupled device architecture.
Atomic ions controlled by laser light are among the leading candidates for large scale quantum computing. However operational systems today require vast scaling to reach levels capable of useful computational tasks. The integration of light delivery will be an essential component of this for the trapped-ion approach. I will describe results in which the use of photonics integrated into ion trap chips has allowed us to perform high fidelity two-qubit gates, which are an essential building block for quantum computers. These systems have now been extended to the operation of multiple trap zones, and the creation of novel optical fields for ion trap control while a new generation of chips allowing integration of all required wavelengths as well as optimised light delivery offers further enhancements in performance and scaling.
Quantinuum has deployed trapped-ion quantum computers based on a quantum charge-coupled (QCCD) architecture exhibiting high-fidelity operations, mid-circuit measurements, and full connectivity with record performance. Quantinuum recently released its accelerated Roadmap outlining plans to reach thousands of physical qubits while further reducing logical qubit error rates in commercial systems by 2029 [1]. Longerterm scaling of the QCCD device architecture will be enabled by replacing bulk free-space optics with integrated photonics for improved light delivery and detection. To this end, Quantinuum is developing integrated photonics technologies at the visible and ultraviolet wavelengths required for future large-scale trapped-ion quantum computers. This poster presents recent developments in materials (waveguiding materials, transparent conductive materials), visible and ultraviolet integrated photonics components for light routing and control, and the various paths to their implementation. These developments are expected to enable scaling towards larger qubit counts while reducing the physical size of the optical control systems.
Trapped-ion quantum computers, leveraging a quantum charge-coupled device (QCCD) architecture, have world-class performance in the field of quantum computing, offering high fidelities and all-to-all connectivity [1]. While systems have advanced over the last decade, much work remains to scale quantum computers to fault-tolerance. Providing scalable light delivery is one key challenge. Current systems utilize engineered bulk- and fiber-optic-based light delivery systems, external to the vacuum chamber, to deliver arrays of beams to ions. However, fundamental optical limitations preclude the use of such systems when scaling beyond thousands of qubits. Integrated photonic-based beam delivery offers a potential solution, with encouraging proof-of-concept demonstrations from the photonics and quantum communities [2]–[5]. Quantinuum and Sandia National Labs have partnered to accelerate the development of integrated photonics for trapped-ion quantum computing applications, working towards photonic components supporting high-fidelity operations. Here, we present development of photonic integrated components designed to deliver laser light toBa+\text{Ba}^{+}Ba+qubits, utilizing a low-loss, high-confinement, trap-integrable PECVD SiN platform. In order to demonstrate two-qubit gates at 532 nm, we developed low loss, tight bend waveguides, efficient edge couplers, and asymmetric multimode interference (MMI) splitters, along with beam-forming grating out-couplers delivering gaussian beams at the ion plane. For quantum state preparation and measurement (SPAM) applications at4 9 3   n m\text{4 9 3 ~ n m}4 9 3   n m, we demonstrate fabrication-tolerant splitters and low-crosstalk gratings. Measured component performance shows promise for future trap-integrated demonstrations.
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 The trapped-ion quantum charge-coupled device (QCCD) proposal1, 2 lays out a blueprint for a universal quantum computer that uses mobile ions as qubits. Analogous to a charge-coupled device (CCD) camera, which stores and processes imaging information as movable electrical charges in coupled pixels, a QCCD computer stores quantum information in the internal state of electrically charged ions that are transported between different processing zones using dynamic electric fields. The promise of the QCCD architecture is to maintain the low error rates demonstrated in small trapped-ion experiments3–5 by limiting the quantum interactions to multiple small ion crystals, then physically splitting and rearranging the constituent ions of these crystals into new crystals, where further interactions occur. This approach leverages transport timescales that are fast relative to the coherence times of the qubits, the insensitivity of the qubit states of the ion to the electric fields used for transport, and the low crosstalk afforded by spatially separated crystals. However, engineering a machine capable of executing these operations across multiple interaction zones with low error introduces many difficulties, which have slowed progress in scaling this architecture to larger qubit numbers. Here we use a cryogenic surface trap to integrate all necessary elements of the QCCD architecture—a scalable trap design, parallel interaction zones and fast ion transport—into a programmable trapped-ion quantum computer that has a system performance consistent with the low error rates achieved in the individual ion crystals. We apply this approach to realize a teleported CNOT gate using mid-circuit measurement6, negligible crosstalk error and a quantum volume7 of 26 = 64. These results demonstrate that the QCCD architecture provides a viable path towards high-performance quantum computers.
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.