An error-protected cross-resonance switch in weakly-tuneable architectures

TL;DR

This paper introduces a method to reduce stray coupling errors in two-qubit microwave gates by combining a tunable coupler with a weakly-tunable qubit, significantly improving switch fidelity in quantum computing.

Contribution

It proposes a novel approach using a weakly-tunable qubit as an optimal coupler to minimize stray coupling errors in two modes of operation.

Findings

Stray coupling errors can be significantly reduced with the proposed method.

The approach enhances the fidelity of quantum switches.

Weakly-tunable qubits improve tuning efficiency and reduce leakage.

Abstract

In two-qubit gates activated by microwave pulses, by turning pulse on or off, the state of qubits are swapped between entangled or idle modes. In either mode, the presence of stray couplings makes qubits accumulate coherent phase error. However, the error rates in the two modes differ because qubits carry different stray coupling strengths in each mode; therefore, eliminating stray coupling from one mode does not remove it from the other. We propose to combine such a gate with a tunable coupler and show that both idle and entangled qubits can become free from stray couplings. This significantly increases the operational switch fidelity in quantum algorithms. We further propose a weakly-tunable qubit as an optimum coupler to bring the two modes parametrically near each other. This remarkably enhances the tuning process by reducing its leakage.