Reducing unitary and spectator errors in cross resonance with optimized rotary echoes

TL;DR

This paper introduces an optimized rotary echo technique for the cross resonance gate that reduces errors and enhances multi-qubit performance in superconducting qubits, leading to higher fidelity and quantum volume.

Contribution

The paper demonstrates a novel application of target rotary pulses to improve cross resonance gate fidelity and reduce spectator errors in superconducting qubits.

Findings

Error terms are reduced with target rotary pulses.

Achieved a new record quantum volume for superconducting qubits.

Improved multi-qubit gate performance and fidelity.

Abstract

We present an improvement to the cross resonance gate realized with the addition of resonant, target rotary pulses. These pulses, applied directly to the target qubit, are simultaneous to and in phase with the echoed cross resonance pulses. Using specialized Hamiltonian error amplifying tomography, we confirm a reduction of error terms with target rotary -- directly translating to improved two-qubit gate fidelity. Beyond improvement in the control-target subspace, the target rotary reduces entanglement between target and target spectators caused by residual quantum interactions. We further characterize multi-qubit performance improvement enabled by target rotary pulsing using unitarity benchmarking and quantum volume measurements, achieving a new record quantum volume for a superconducting qubit system.