Low-loss interconnects for modular superconducting quantum processors

TL;DR

This paper demonstrates low-loss interconnects for modular superconducting quantum processors, enabling high-fidelity quantum state transfer and entanglement across multiple modules, advancing scalable quantum computing architectures.

Contribution

It introduces pure aluminium coaxial cables and on-chip impedance transformers as low-loss interconnects, achieving performance comparable to qubits on single-crystal sapphire and enabling multi-module entanglement.

Findings

Inter-module quantum state transfer fidelity up to 99%

Generation of 4-qubit GHZ states with 92% fidelity

Entanglement of up to 12 qubits with over 55% fidelity

Abstract

Scaling is now a key challenge in superconducting quantum computing. One solution is to build modular systems in which smaller-scale quantum modules are individually constructed and calibrated, and then assembled into a larger architecture. This, however, requires the development of suitable interconnects. Here, we report low-loss interconnects based on pure aluminium coaxial cables and on-chip impedance transformers featuring quality factors up to $8.1 \times 10^5$, which is comparable to the performance of our transmon qubits fabricated on single-crystal sapphire substrate. We use these interconnects to link five quantum modules with inter-module quantum state transfer and Bell state fidelities up to 99\%. To benchmark the overall performance of the processor, we create maximally-entangled, multi-qubit Greenberger-Horne-Zeilinger (GHZ) states. The generated inter-module four-qubit GHZ state exhibits 92.0\% fidelity. We also entangle up to 12 qubits in a GHZ state with $55.8 \pm 1.8\%$ fidelity, which is above the genuine multipartite entanglement threshold of 1/2. These results represent a viable modular approach for large-scale superconducting quantum processors.