Tunable Hybrid-Mode Coupler Enabling Strong Interactions between Transmons at Centimeter-Scale Distance

TL;DR

This paper presents a novel hybrid-mode coupler that enables strong, tunable interactions between transmon qubits separated by centimeters, significantly extending quantum connectivity for scalable superconducting quantum processors.

Contribution

Introduction of a hybrid-mode coupler leveraging resonator-transmon hybridization to achieve high-contrast, tunable coupling between centimeter-scale transmons.

Findings

Achieved flux-tunable $XX$ coupling up to 23 MHz.

Realized $ZZ$ coupling strengths reaching 100 MHz.

Demonstrated agreement with an effective two-channel model.

Abstract

The transmon, a fabrication-friendly superconducting qubit, remains a leading candidate for scalable quantum computing. Recent advances in tunable couplers have accelerated progress toward high-performance quantum processors. However, extending coherent interactions beyond millimeter scales to enhance quantum connectivity presents a critical challenge. Here, we introduce a hybrid-mode coupler exploiting resonator-transmon hybridization to simultaneously engineer the two lowest-frequency mode, enabling high-contrast coupling between centimeter-scale transmons. For a 1-cm coupler, our framework predicts flux-tunable $XX$ and $ZZ$ coupling strengths reaching 23 MHz and 100 MHz, with modulation contrasts exceeding $10^2$ and $10^4$, respectively, demonstrating quantitative agreement with an effective two-channel model. This work provides an efficient pathway to mitigate the inherent connectivity constraints imposed by short-range interactions, enabling transmon-based architectures compatible with hardware-efficient quantum tasks.