Composite two-qubit gates

TL;DR

This paper introduces composite two-qubit controlled-phase gates that significantly improve error robustness in quantum computing, with methods to cancel various errors and an ion-trap implementation demonstrating practical advantages.

Contribution

The authors develop composite sequences for two-qubit gates that are robust to multiple error types and provide a practical ion-trap implementation.

Findings

Robust composite sequences up to 6th order error correction

Absolute error cancellation with only two gates

Ion-trap implementation with simultaneous error cancellation

Abstract

We design composite controlled-phase gates, which compensate errors in the phase of a single gate. The errors can be of various nature, such as relative, absolute or both. We present composite sequences which are robust to relative errors up to the 6th order, with the number of the constituent gates growing just linearly with the desired accuracy, and we describe a method to achieve even higher accuracy. We show that the absolute error can be canceled entirely with only two gates. We describe an ion-trap implementation of our composite gates, in which simultaneous cancellation of the error in both the pulse area and the detuning is achieved.