Roadmap to planar electron-ion point Paul trap

TL;DR

The paper addresses building a hybrid quantum platform by co-trapping laser-cooled Ca+ ions and a single electron in a planar two-frequency Paul trap. It provides a concrete planar-design blueprint, including electrode geometry and a copper-coated glass manufacturing method, and analyzes field symmetry, trap depth, and heating using both copper and superconducting films. Heating is shown to be dominated by Johnson–Nyquist noise, with cryogenic operation and superconducting films offering substantial reductions in decoherence and deeper traps (up to ~$D\approx 10^2$ K in simulations). The work outlines practical pathways for integrating dozens of ions with trapped electrons for quantum sensing and fast electron-qubit operations, emphasizing plans for improved materials, photonic integration, and scalable fabrication.

Abstract

We present a technical guide to developing a quantum-mechanical system with co-trapped laser-cooled ions and electrons, aiming to utilize this mixed-species system in quantum computing and sensing. We outline a method to control the system's quantum state and provide a blueprint for a forward-compatible design for containing it. The proposed technical solution features a planar configuration with a large trapping volume located at a considerable height above the electrode plane. We detail a manufacturing method using copper-coated, laser-machined glass substrates suitable for a high-power microwave drive signal. We discuss electron state decoherence in this trap and suggest that using superconductive films could enhance trapping abilities, though initial experiments are feasible with the current design.

Figures (16)

• Figure 1: Radial part of the potential experienced by the electron, and its regions, marked as enumerated in Section \ref{['sec:categories']}. The boundaries of the transition region 2 are selected as energies, at which the combined potential starts deviating from the Coulomb or effective harmonic profile by more than 10%. The figure neglects the influence of slowly varying ion trapping field, for that can be dealt as a perturbation under certain conditions mentioned in Section \ref{['sec:trappingpotentials']}.
• Figure 2: Energy levels of an electron-Ca^2+ system confined within a spherically symmetric trapping potential. For clarity, only every 50th energy level of states with zero angular momentum is plotted. As the Coulomb well deforms the harmonic potential, the extrapolation of the linear dependence does not intersect the origin.
• Figure 3: Energy levels and transitions used in the experiments with the Ca^2+-electron system. The wavelength values and nomenclature of the beams are given in Table \ref{['tab:beams']}. TI, also dash dot lines -- trap-induced levels. Not to scale.
• Figure 4: Tuning transition 5 (as depicted in Figure \ref{['fig:levels']}) adjusting electron trapping voltage amplitude $V_\mathrm{e0}$. The variation of energy required to alter the quantum number of the model system from Figure \ref{['fig:energylevels']} by one is demonstrated for states located in the harmonic-potential region ($n=2698$), transition region ($n = 1205$) and the Coulomb potential well ($n=287$) in relation to the trapping parameter. $\Delta E_0$ refers to the transition energy at the initial value of the amplitude $V_\mathrm{e0} = \qty{88}{V}$.
• Figure 5: Electrode configuration of ring trap, a.k.a. point Paul trap used in this study. View from top. The driving signal with frequency $\Omega_\mathrm{e}$ is delivered to electrode sectors marked "e". The signal with frequency $\Omega_\mathrm{I}$ is delivered to electrodes marked "I". The outermost electrode extends to the edges of the wafer.