Individually Addressed Entangling Gates in a Two-Dimensional Ion Crystal

TL;DR

This paper demonstrates high-fidelity two-qubit entangling gates between any ion pairs in a 2D ion crystal, overcoming challenges of micromotion and addressing crosstalk, advancing scalable quantum computing with ion traps.

Contribution

It introduces a method for implementing universal two-qubit gates in 2D ion crystals with low crosstalk and micromotion compensation, enabling scalable quantum computing.

Findings

Achieved <0.1% addressing crosstalk error.

Demonstrated gate fidelity unaffected by micromotion after recalibration.

Implemented a gate sequence compatible with single-ion addressing techniques.

Abstract

Two-dimensional (2D) ion crystals have become a promising way to scale up qubit numbers for ion trap quantum information processing. However, to realize universal quantum computing in this system, individually addressed high-fidelity two-qubit entangling gates still remain challenging due to the inevitable micromotion of ions in a 2D crystal as well as the technical difficulty in 2D addressing. Here we demonstrate two-qubit entangling gates between any ion pairs in a 2D crystal of four ions. We use symmetrically placed crossed acousto-optic deflectors (AODs) to drive Raman transitions and achieve an addressing crosstalk error below 0.1%. We design and demonstrate a gate sequence by alternatingly addressing two target ions, making it compatible with any single-ion addressing techniques without crosstalk from multiple addressing beams. We further examine the gate performance versus the micromotion amplitude of the ions and show that its effect can be compensated by a recalibration of the laser intensity without degrading the gate fidelity. Our work paves the way for ion trap quantum computing with hundreds to thousands of qubits on a 2D ion crystal.