Researchers at the University of California, Riverside have demonstrated how quantum computers can be scaled up by connecting multiple small chips to function as a single unit. The study, published in Physical Review A, suggests that even with imperfect connections between these chips, it is possible to create a reliable and fault-tolerant quantum system.
“Our work isn’t about inventing a new chip,” said Mohamed A. Shalby, the first author of the paper and a doctoral candidate in the UCR Department of Physics and Astronomy. “It’s about showing that the chips we already have can be connected to create something much larger and still work. That’s a foundational shift in how we build quantum systems.”
The research addresses challenges in scaling quantum hardware for practical applications. Scaling involves managing increasing amounts of data without performance failure, while fault tolerance allows a system to detect and correct errors automatically.
“In practice, connecting multiple smaller chips has been difficult,” Shalby said. “Connections between separate chips — especially those housed in separate cryogenic refrigerators — are much noisier than operations within a single chip. This increased noise can overwhelm the system and prevent error correction from working properly.”
Despite this challenge, simulations conducted by the team showed that even when links between chips were up to ten times noisier than the chips themselves, error detection and correction remained effective.
“This means we don’t have to wait for perfect hardware to scale quantum computers,” Shalby said. “We now know that as long as each chip is operating with high fidelity, the links between them can be ‘good enough’ — not perfect — and we can still build a fault-tolerant system.”
Shalby explained that building reliable quantum computers requires more than just increasing qubit numbers; clusters of physical qubits are used to form logical qubits capable of correcting errors inherent in quantum systems. The surface code method is commonly used for this purpose.
According to Shalby, “Until now, most quantum milestones focused on increasing the sheer number of qubits. But without fault tolerance, those qubits aren’t useful. Our work shows we can build systems that are both scalable and reliable — now, not years from now.”
The research was inspired by previous work at Massachusetts Institute of Technology and supported by funding from the National Science Foundation. Simulations utilized tools developed by Google Quantum AI.
Other contributors included Leonid P. Pryadko and Renyu Wang from UCR and Denis Sedov from University of Stuttgart.
The paper is titled “Optimized noise-resilient surface code teleportation interfaces.”
