High-fidelity spatial and polarization addressing of Ca-43 qubits using near-field microwave control

TL;DR

This paper demonstrates high-fidelity spatial and polarization microwave control of Ca-43 ion qubits in a microfabricated trap, enabling scalable quantum computing with minimal crosstalk and off-resonant errors.

Contribution

It introduces a method for spatially and polarization-selective microwave addressing of ion qubits in a microfabricated trap, advancing scalable quantum information processing.

Findings

Achieved a Rabi frequency ratio of up to 1400 between addressed and non-addressed qubits.

Measured a spin-flip probability of 1.3×10⁻⁶ for non-addressed qubits.

Implemented polarization control with an error of 2×10⁻⁵ to suppress off-resonant excitation.

Abstract

Individual addressing of qubits is essential for scalable quantum computation. Spatial addressing allows unlimited numbers of qubits to share the same frequency, whilst enabling arbitrary parallel operations. We demonstrate addressing of long-lived $^{43}\text{Ca}^+$ "atomic clock" qubits held in separate zones ($960\mu$m apart) of a microfabricated surface trap with integrated microwave electrodes. Such zones could form part of a "quantum CCD" architecture for a large-scale quantum information processor. By coherently cancelling the microwave field in one zone we measure a ratio of Rabi frequencies between addressed and non-addressed qubits of up to 1400, from which we calculate a spin-flip probability on the qubit transition of the non-addressed ion of $1.3\times 10^{-6}$. Off-resonant excitation then becomes the dominant error process, at around $5 \times 10^{-3}$. It can be prevented either by working at higher magnetic field, or by polarization control of the microwave field. We implement polarization control with error $2 \times 10^{-5}$, which would suffice to suppress off-resonant excitation to the $\sim 10^{-9}$ level if combined with spatial addressing. Such polarization control could also enable fast microwave operations.