[Paper Review] Characterization of Inner Control Electrode Shapes for Multi-Layer Surface-Electrode Ion Traps

Florian Ungerechts, Brigitte Kaune+1 more|arXiv (Cornell University)|Feb 27, 2026

Electrochemical Analysis and Applications0 citations

TL;DR

The paper evaluates asymmetric inner control electrode shapes for multi-layer surface-electrode ion traps, demonstrating that certain shapes enable simultaneous axial and radial control without outer electrodes, and assessing transport and micromotion compensation performance.

ABSTRACT

Microfabricated surface-electrode traps are a scalable platform for trapped-ion quantum processors. Recent advances in fabrication techniques have enabled the design of increasingly complex multi-layer structures. Yet the control electrodes remain mostly unchanged and of rectangular shape. We systematically analyze asymmetric inner control electrode shapes for simultaneous axial and radial control in multi-layer surface traps, characterize and compare a selection of different shapes, and verify their capabilities in realistic use-case scenarios for ion transport and micromotion compensation. Eliminating the need for the commonly used additional outer control electrodes, asymmetric inner control electrodes increase the compactness and space efficiency of surface-electrode traps while concurrently reducing the number of control signals. The improved control voltage efficiency of using solely inner electrodes enables the device's entire direct-current (DC) supply to be provided by integrated Cryo-CMOS circuits, further enhancing the scalability of the processor.

Motivation & Objective

• Motivate scalable trapped-ion quantum processors using multi-layer surface-electrode traps.
• Investigate whether asymmetric inner control electrode shapes can provide simultaneous axial and radial control without outer DC electrodes.
• Quantify how different shapes influence potential derivatives and Hessian components at unit voltage.
• Assess practical performance in ion transport and micromotion compensation scenarios.

Proposed method

• Use Gapless Plane Approximation to compute basis functions and potentials for arbitrarily shaped inner DC electrodes.
• Normalize electrode areas so potentials are comparable across shapes (reference area = 1650 μm^2 per single electrode).
• Hold each candidate inner electrode at -1 V and map normalized static potential and its first- and second-order derivatives at h_ion = 70.1 μm.
• Evaluate Hessian-derived curvatures to infer motional mode frequencies and possible rotations of the ion's oscillation basis.
• Apply a convex optimization solver to compute transport voltages for 12 active electrodes under constraints, minimizing a weighted sum of voltages and second derivatives.
• Test shim-field generation by solving for static fields in x, y, z directions with zero secondary derivatives except allowed ones.

Experimental results

Research questions

• RQ1 Can asymmetric inner control electrode shapes provide simultaneous axial and radial control without outer DC electrodes?
• RQ2 Which shapes yield sufficient first- and second-order potential derivatives to enable ion transport and micromotion compensation?
• RQ3 How do different shapes compare in terms of required transport voltages and axial trap depth during transport?
• RQ4 Which shapes can generate the necessary shim fields for precise micromotion compensation across all directions?

Key findings

• Asymmetric inner control electrodes enable simultaneous axial and radial control without outer electrodes.
• Rectangular inner electrodes with axial and radial segmentation perform best overall, followed by triangular, then ‘T’- and ‘L’-shaped shapes; rhomboid and ‘Z’-shaped shapes underperform in some directions.
• Unit-voltage analysis shows derivatives in y-direction are strongest for axially/radially segmented shapes; rectangular shapes fail to provide y-derivative.
• Ion-transport tests (10 mm trap, Be+ ions, U_RF = 75 V, f_RF = 88.191 MHz) show all asymmetric shapes can achieve transport with feasible voltages; rhomboid and Z-shaped shapes require higher voltages and sometimes exceed practical constraints.
• Axial trap depth during transport is similar for rectangular, radially segmented rectangular, and ‘L’-shaped electrodes, while triangular and ‘T’-shaped can increase depth by about 30%; rhomboid and Z-shaped yield larger depths due to higher voltages.
• Micromotion shim tests indicate most asymmetric shapes provide all necessary shim fields; rhomboid and Z-shaped often fail to provide some shim fields under voltage limits.