Scientists build modular quantum computers like Lego blocks Researchers from the University of Illinois Urbana-Champaign have achieved a breakthrough in quantum computing by developing a modular architecture that allows superconducting quantum processors to be interconnected like building blocks, potentially overcoming major scaling barriers that have limited quantum computer development. The team demonstrated approximately 99% fidelity in quantum gate operations between separate devices connected by superconducting coaxial cables. Published in Nature Electronics, the research addresses a fundamental challenge in quantum computing: building large-scale systems with millions of qubits while maintaining the precision required for quantum operations. Traditional monolithic quantum computers, built as single large units, face significant limitations in size and performance, making modular approaches increasingly attractive to the field. Engineering-Friendly Modularity Wolfgang Pfaff, an assistant professor of physics at the University of Illinois and senior author of the study, described the innovation as "an engineering-friendly way of achieving modularity with superconducting qubits". The system enables researchers to build, test, and connect separate quantum modules, providing the flexibility to reconfigure systems and identify problems before full assembly. "Can I build a system that I can bring together, allowing me to manipulate two qubits jointly so as to create entanglement or gate operations between them? Can we do that at a very high quality?" Pfaff explained. "Typically, we only find out that something went wrong after putting it together. So we would really like to have the ability to reconfigure the system later". The team achieved their results by connecting two quantum devices with superconducting coaxial cables, demonstrating SWAP gate operations with less than 1% loss. This level of performance rivals systems where components are permanently bonded together, according to research published on arXiv. Industry-Wide Push for Modularity The Illinois breakthrough comes amid broader industry efforts to scale quantum computing through modular approaches. IBM has incorporated modularity into its roadmap for building fault-tolerant quantum computers, with processors like Kookaburra and Cockatoo designed to connect multiple quantum chips. The company aims to deliver its Quantum Starling system by 2029, capable of running 100 million quantum gates on 200 logical qubits. Other research groups have achieved similar advances in modular quantum systems. A team at Southern University of Science and Technology previously demonstrated 99% quantum state transfer fidelity between modules and created entangled states across multiple quantum chips. Meanwhile, researchers at the University of Chicago have developed a different modular approach using reconfigurable routers to connect qubits. Scaling Challenges Ahead Despite the promising results, significant challenges remain in scaling modular quantum systems. Pfaff acknowledged that the next phase involves connecting more than two devices while maintaining error detection and correction capabilities. The team's current connector hardware impacts qubit coherence, though improvements could potentially achieve gate infidelities approaching one part in a thousand. "Finding an approach that works has taken a while for our field," Pfaff noted. "Many groups have figured out that what we really want is this ability to stitch bigger and bigger things together through cables, and at the same time reach numbers that are good enough to justify scaling". The research represents a step toward quantum computers capable of solving practical problems beyond the reach of classical computers, with modularity offering a path to the millions of qubits needed for applications in drug discovery, materials science, and cryptography.
