Robust Two-Qubit Gates Using Pulsed Dynamical Decoupling

TL;DR

This paper demonstrates a high-fidelity, robust two-qubit phase gate in a trapped-ion quantum processor using pulsed dynamical decoupling, with potential for fast, resource-efficient quantum operations.

Contribution

The authors experimentally implement a laser-free, RF-driven two-qubit phase gate using pulsed dynamical decoupling, showing robustness and high fidelity in trapped-ion systems.

Findings

Achieved up to 99% fringe contrast in Ramsey measurements.

Gate robustness against mode excitation, trap frequency errors, and pulse errors.

Potential for fast gate speeds around 100 microseconds.

Abstract

We present the experimental implementation of a two-qubit phase gate, using a radio frequency (RF) controlled trapped-ion quantum processor. The RF-driven gate is generated by a pulsed dynamical decoupling sequence applied to the ions' carrier transitions only. It allows for a tunable phase shift with high-fidelity results, in particular a fringe contrast up to $99_{-2}^{+1}\%$ is observed in Ramsey-type measurements. We also prepare a Bell state using this laser-free gate. The phase gate is robust against common sources of error. We investigate the effect of the excitation of the center-of-mass (COM) mode, errors in the axial trap frequency, pulse area errors and errors in sequence timing. The contrast of the phase gate is not significantly reduced up to a COM mode excitation $<20$ phonons, trap frequency errors of +10%, and pulse area errors of -8%. The phase shift is not significantly affected up to $<10$ phonons and pulse area errors of -2%. Both, contrast and phase shift are robust to timing errors up to -30% and +15%. The gate implementation is resource efficient, since only a single driving field is required per ion. Furthermore, it holds the potential for fast gate speeds (gate times on the order of $100~\mu$s) by using two axial motional modes of a two-ion crystal through improved setups.