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International Symposium on Physical Design

An Improved Ion-Shuttling Approach for QCCD Architectures

Tung-Yeh Wu, Ting-Chi Wang

Published Mar 15, 2026• 0 citations
Publisher

Abstract

Trapped-ion quantum computers offer high-fidelity operations, long coherence times, and all-to-all connectivity within a single trap. However, scaling to large circuits is limited by the trap's ion capacity. The QCCD architecture addresses this by enabling ion shuttling across multiple traps, but excessive shuttling increases execution time and degrades fidelity. This paper presents an improved ion-shuttling approach targeting linear QCCD architectures. Building on a state-of-the-art approach [27] for linear trapped-ion devices, our approach introduces a front-layer-based scheduling method that dynamically prioritizes executable gates, along with a novel destination trap selection method for ion-shuttling, effectively reducing unnecessary ion movements. We also present a look-ahead gate selection strategy based on the gate dependency graph, avoiding the high runtime of the gate proximity approach used in the state-of-the-art approach, especially in circuits with all-to-all communication. Our approach achieves up to a 37.67% reduction in shuttle count and up to a 74.91% reduction in compilation time compared to the state-of-the-art approach for linear trapped-ion devices on actual NISQ benchmarks and synthetic circuits. On average, our approach achieves a 16.44% reduction in shuttle count and a 30.77% reduction in compilation time across all test cases. These improvements highlight the effectiveness of our approach, particularly for actual circuits.

DOI
10.1145/3764386.3779585

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Trapped-ion quantum computers offer high-fidelity operations, long coherence times, and all-to-all connectivity within a single trap. However, scaling to large circuits is limited by the trap's ion capacity. The QCCD architecture addresses this by enabling ion shuttling across multiple traps, but excessive shuttling increases execution time and degrades fidelity. This paper presents an improved ion-shuttling approach targeting linear QCCD architectures. Building on a state-of-the-art approach [27] for linear trapped-ion devices, our approach introduces a front-layer-based scheduling method that dynamically prioritizes executable gates, along with a novel destination trap selection method for ion-shuttling, effectively reducing unnecessary ion movements. We also present a look-ahead gate selection strategy based on the gate dependency graph, avoiding the high runtime of the gate proximity approach used in the state-of-the-art approach, especially in circuits with all-to-all communication. Our approach achieves up to a 37.67% reduction in shuttle count and up to a 74.91% reduction in compilation time compared to the state-of-the-art approach for linear trapped-ion devices on actual NISQ benchmarks and synthetic circuits. On average, our approach achieves a 16.44% reduction in shuttle count and a 30.77% reduction in compilation time across all test cases. These improvements highlight the effectiveness of our approach, particularly for actual circuits.
Trapped-ion quantum computers are a promising platform, offering high-quality qubits with long coherence times and high-fidelity gate operations. The Quantum Charge Coupled Device (QCCD) architecture provides a scalable blueprint by leveraging the ability to shuttle ions between distinct zones. However, realizing such architectures in practice requires software support to manage ion movement across multi-zone layouts. In this work, we propose a compilation strategy for QCCD architectures with multiple processing zones located outside a grid-type memory zone. Unlike previous approaches that treat processing zones as black-boxes, our method explicitly models their structural constraints, enabling optimized ion movement to and through them. It combines qubit partitioning with dependency-aware gate selection to reduce inter-zone shuttling while enabling simultaneous gate execution. We implemented the method in an open-source tool and empirically demonstrated its effectiveness across several QCCD layouts, laying a foundation for the compilation of multi-zone trapped-ion systems.
Ion trap technologies have earned significant attention as potential candidates for quantum information processing due to their long decoherence times and precise manipulation of individual qubits, distinguishing them from other candidates in the field of quantum technologies. However, scalability remains a challenge, as introducing additional qubits into a trap increases noise and heating effects, consequently decreasing operational fidelity. Trapped-ion Quantum Charge-Coupled Device (QCCD) architectures have addressed this limitation by interconnecting multiple traps and employing ion shuttling mechanisms to transfer ions among traps. This new architectural design requires the development of novel compilation techniques for quantum algorithms, which efficiently allocate and route qubits, and schedule operations. The aim of a compiler is to minimize ion movements and, therefore, reduce the execution time of the circuit to achieve a higher fidelity. In this paper, we propose a novel approach for initial qubit placement, demonstrating enhancements of up to 50% compared to prior methods. Furthermore, we conduct a scalability analysis on two distinct QCCD topologies: a 1D-linear array and a ring structure. Additionally, we evaluate the impact of the excess capacity - i.e. the number of free spaces within a trap - on the algorithm performance.
Trapped ions (TI) are at the forefront of quantum computing implementation, offering unparalleled coherence, fidelity, and connectivity. However, the scalability of TI systems is hampered by the limited capacity of individual ion traps, necessitating intricate ion shuttling for advanced computational tasks. The Quantum Charge-Coupled Device (QCCD) framework has emerged as a promising solution, facilitating ion mobility for universal quantum computation. Current QCCD architectures predominantly feature a linear topology, which is increasingly recognized as inefficient for complex quantum operations. Anticipating the shift towards more efficacious designs, this paper introduces an innovative quantum scheduling strategy optimized for parallel QCCD topologies. Our strategy proposes a probabilistic formula for ion movement, alongside ingenious methods for local layer generation and layer compression, yielding a significant reduction in ion shuttle times. Through simulations, we demonstrate that our strategy not only substantially outstrips the linear model but also exhibits better performance over other parallel strategies that employ greedy algorithms. This is achieved through our nuanced resolution of complexities such as traffic blocks and trap capacity limitations. The consequent reduction in shuttle operations leads to lower energy consumption and an enhancement in the quantum computer's fidelity, ultimately accelerating program execution times.
The Quantum Charge Coupled Device (QCCD) architecture is a promising pathway toward scalable quantum computation in trapped-ion quantum computers. Devices using this architecture rely on efficient ion shuttling between memory and processing zones to execute quantum circuits. Hardware for trapped-ion quantum computers with multiple different zones is already being developed, but without proper compilation support, there is a risk that we will not be able to use their full potential. Recent approaches to shuttling algorithms have primarily focused on small architectures or devices with a single processing zone. In this work, we propose to extend these algorithms to large grid-type systems with multiple processing zones embedded in the memory zone. For that, a two-step solution is described: first, partitioning quantum circuits to determine where each gate is executed, and second, adapting a publicly available shuttling algorithm for architectures with a single processing zone to handle the increased complexity of multi-zone systems. Empirical evaluations demonstrate the method's effectiveness across a range of grid-type architectures, showing that additional processing zones can significantly reduce quantum circuit execution time. With that, we provide a foundation for the compilation of shuttling-based trapped-ion quantum computers with multiple processing zones. An open-source implementation of the proposed approach is available at https://github.com/cda-tum/mqt-ion-shuttler.
Trapped-ion systems can have a limited number of ions (qubits) in a single trap. Increasing the qubit count to run meaningful quantum algorithms would require multiple traps where ions need to shuttle between traps to communicate. The existing compiler has several limitations, which result in a high number of shuttle operations and degraded fidelity. In this paper, we target this gap and propose compiler optimizations to reduce the number of shuttles. Our technique achieves a maximum reduction of 51.17% in shuttles (average ~ 33%) tested over 125 circuits. Furthermore, the improved compilation enhances the program fidelity up to 22.68X with a modest increase in the compilation time.
Trapped-ion Quantum Charge-Coupled Device (QCCD) architectures promise scalability through interconnected trap zones and dynamic ion transport; however, this transport capability creates a complex compilation challenge: how to move qubits efficiently without degrading fidelity. We introduce a routing strategy that turns this challenge into an advantage by exploiting operational parallelism across traps while adapting to both algorithmic structure and device topology through a configurable multi-parameter scoring mechanism. Across a broad suite of benchmarks and QCCD layouts, the method consistently reduces ion-transport overhead and improves execution fidelity, outperforming state-of-the-art routing techniques. These results highlight that explicitly balancing movement overhead and execution parallelism under architectural constraints is key to unlocking the full potential of modular trapped-ion quantum processors.