Long-Range $ZZ$ Interaction via Resonator-Induced Phase in Superconducting Qubits

TL;DR

This paper introduces a resonator-based scheme to extend the range of qubit interactions in superconducting quantum computers, significantly improving connectivity and enabling scalable, fault-tolerant quantum processing.

Contribution

It proposes a multimode coupling method using resonator-induced phase gates to achieve long-range $ZZ$ interactions between superconducting qubits.

Findings

Achieved >99.9% fidelity CZ gate within 160 ns at 1.4 GHz FSR.

Reduced residual photon to ~10^{-3} within 100 ns at 0.2 GHz FSR.

Enabled long-range qubit interactions over sub-meter separations.

Abstract

Superconducting quantum computing emerges as one of leading candidates for achieving quantum advantage. However, a prevailing challenge is the coding overhead due to limited quantum connectivity, constrained by nearest-neighbor coupling among superconducting qubits. Here, we propose a novel multimode coupling scheme using three resonators driven by two microwaves, based on the resonator-induced phase gate, to extend the $ZZ$ interaction distance between qubits. We demonstrate a CZ gate fidelity exceeding 99.9\% within 160 ns at free spectral range (FSR) of 1.4 GHz, and by optimizing driving pulses, we further reduce the residual photon to nearly $10^{-3}$ within 100 ns at FSR of 0.2 GHz. These facilitate the long-range CZ gate over separations reaching sub-meters, thus significantly enhancing qubit connectivity and making a practical step towards the scalable integration and modularization of quantum processors. Specifically, our approach supports the implementation of quantum error correction codes requiring high connectivity, such as low-density parity check codes that paves the way to achieving fault-tolerant quantum computing.