Crosstalk Suppression in Individually Addressed Two-Qubit Gates in a Trapped-Ion Quantum Computer

TL;DR

This paper presents a method to actively cancel crosstalk errors in two-qubit gates of a trapped-ion quantum computer, significantly improving fidelity by using local echoing pulses.

Contribution

The authors introduce a crosstalk suppression scheme that eliminates first-order errors with local control, applicable to various quantum platforms.

Findings

Achieved two-qubit Bell state fidelity of 99.52% with echoing pulses after collective gates.

Demonstrated fidelity of 99.37% with local echoing pulses on each gate.

Scheme effectively cancels residual crosstalk in a 5-ion chain.

Abstract

Crosstalk between target and neighboring spectator qubits due to spillover of control signals represents a major error source limiting the fidelity of two-qubit entangling gates in quantum computers. We show that in our laser-driven trapped-ion system coherent crosstalk error can be modelled as residual $X\hat{\sigma}_{\phi}$ interaction and can be actively cancelled by single-qubit echoing pulses. We propose and demonstrate a crosstalk suppression scheme that eliminates all first-order crosstalk, yet only requires local control by driving rotations solely on the target qubits. We report a two-qubit Bell state fidelity of $99.52(6) \%$ with the echoing pulses applied after collective gates and $99.37(5) \%$ with the echoing pulses applied to each gate in a 5-ion chain. This scheme is widely applicable to other platforms with analogous interaction Hamiltonians.