Scalable Multispecies Ion Transport in a Grid-Based Surface-Electrode Trap (2403.00756v2)

Abstract: Quantum processors based on linear arrays of trapped ions have achieved exceptional performance, but scaling to large qubit numbers requires realizing two-dimensional ion arrays as envisioned in the quantum charge-coupled device (QCCD) architecture. Here we present a scalable method for the control of ion crystals in a grid-based surface-electrode Paul trap and characterize it in the context of transport operations that sort and reorder multispecies crystals. By combining cowiring of control electrodes at translationally symmetric locations in each grid site with the sitewise ability to exchange the voltages applied to two special electrodes gated by a binary input, site dependent operations can be achieved using only a fixed number of analog voltage signals and a single digital input per site. In two separate experimental systems containing nominally identical grid traps, one using $^{171}\mathrm{Yb}^{+}$-$^{138}\mathrm{Ba}^{+}$ crystals and the other $^{137}\mathrm{Ba}^{+}$-$^{88}\mathrm{Sr}^{+}$, we demonstrate this method by characterizing the conditional intrasite crystal reorder and the conditional exchange of ions between adjacent sites on the grid. Averaged across a multisite region of interest, we measure subquanta motional excitation in the axial in-phase and out-of-phase modes of the crystals following these operations at exchange rates of 2.5 kHz. In this initial demonstration, the logic controlling the voltage exchange occurs in software, but the applied signals mimic a proposed hardware implementation using crossover switches. These techniques can be further extended to implement other conditional operations in the QCCD architecture such as gates, initialization and measurement.

• The paper introduces a scalable method for ion transport using grid-based surface-electrode traps in the QCCD architecture.
• It employs a novel C2LR transport primitive and co-wired electrode control to achieve ion swap speeds up to 3.2 kHz with minimal motional excitation.
• Experimental validation in Yb-Ba and Ba-Sr systems confirms the method's potential for advancing scalable quantum computing architectures.

Overview of Scalable Multispecies Ion Transport in a Grid-Based Surface-Electrode Trap

The paper "Scalable Multispecies Ion Transport in a Grid-Based Surface-Electrode Trap" presents a scalable methodology for controlling ion crystals in a two-dimensional grid-based surface-electrode Paul trap, particularly in the context of the quantum charge-coupled device (QCCD) architecture. The research primarily discusses methodologies to enhance the scalability of quantum processors by leveraging a combination of control strategies for multispecies ions and addressing the control scalability issues associated with larger qubit populations.

Key Concepts and Methodology

Traditional ion trap designs, typically linear ones, are noted for their challenges in scaling, hence the research pivots towards exploring two-dimensional grid-based arrays. This approach aligns with the QCCD architecture, which is recognized for its potential in large-scale quantum computing. The paper introduces a transport primitive called center to left or right (C2LR), which is key to enabling flexible control over the ion pathways.

• Control Mechanics: The paper utilizes a novel method of co-wiring control electrodes combined with site-specific voltage manipulations through a single digital input per site. This significantly reduces the analog voltage signals needed, enhancing the feasibility of scaling.
• Conditional Operations: In the experiments, they demonstrate that ions can be transported conditionally—specifically, the reorder and exchange of ions between sites based on these new control protocols. This is pivotal for conducting quantum algorithms that require dynamic qubit interactions in quantum information processing.
• Experimental Implementations: Two separate systems containing grid traps, using ions $^{171}\mathrm{Yb}^{+}$-$^{138}\mathrm{Ba}^{+}$ and $^{137}\mathrm{Ba}^{+}$-$^{88}\mathrm{Sr}^{+}$, were used to validate the scalability approach. Results indicate successful retention of motional ground states post-transport operations, even at exchange rates of 2.5 kHz.

Results and Numerical Analysis

The successful implementation of the C2LR primitive, as reported, was characterized by measurable performance improvements:

1. Motional Excitation: The experiments established subquantal motional excitation post-transport, showcasing minimal energy absorption in Yb-Ba and Ba-Sr crystal pairs, essential for preserving qubit fidelity.
2. Transport Speed: Effective swap operations with minimal excitation were achieved at speeds up to 3.2 kHz, indicating robust system performance under scalable conditions.
3. Implementation Fidelity: The research claims that the controlled ion swapping and reordering can be extended further for operations like gates, initialization, and measurement, suggesting broader applicability within the QCCD framework.

Implications and Future Directions

This paper offers several practical implications, especially in making large scale ion traps realizable by tackling previously challenging control and scaling issues through innovative approaches to electrode control.

• Hardware Development: The proposed strategy promotes the integration of dynamic control systems, potentially leading to advancements in cryogenic CMOS technology and facilitating the distribution of control hardware within the vacuum environment, a known challenge in scaling quantum systems.
• Quantum Computing Potential: By ensuring uniform motional coherence during ion transport in a larger grid, this research supports the development of more complex quantum circuits and error correction protocols crucial for reliable quantum computation.

In summary, the research sets a foundation for future advances in large-scale quantum computing by demonstrating a systematic, scalable approach to multispecies ion transport in grid-based traps. It opens a viable path for the development of long-term quantum computing technologies, aligning with the industry's goals of creating fault-tolerant quantum computers.