Robust entanglement by continuous dynamical decoupling of the J-coupling interaction

TL;DR

This paper introduces a robust, laser-free entangling gate for ions using continuous dynamical decoupling to suppress dephasing, enabling high-fidelity operations resilient to noise and motional decoherence.

Contribution

It presents a novel continuous dynamical decoupling method for J-coupling based entangling gates that are insensitive to amplitude noise and qubit frequency fluctuations.

Findings

Achieves high fidelities below fault-tolerance thresholds.

Operates effectively at high initial temperatures without sideband cooling.

Enables tuning and parallel implementation of gates within ion chains.

Abstract

We propose a $\sigma_z\otimes \sigma_z$ laser-free entangling gate which uses the intrinsic J-coupling of ions in a static magnetic gradient. Dephasing of the interaction is suppressed by means of continuous dynamical decoupling using pairs of microwave fields. The gate is virtually insensitive to common amplitude noise of the microwave fields and enables high fidelities despite qubit frequency fluctuations, while the J-coupling interaction's inherent robustness to motional decoherence is retained. Errors far below the fault-tolerant threshold can be achieved at high initial temperatures, negating the requirement of sideband cooling below the Doppler temperature. By adjusting the powers of the continuous microwave fields, the J-coupling interaction can be tuned and can be used to implement parallel entangling gates within an ion chain.