These quantum switches need a materials makeover

Quantum computers could be chemistry’s next big tool, helping researchers run ever more complex simulations, model molecules, and design new materials from first principles. But some researchers believe that vision is unlikely to materialize without breakthroughs made by the very chemists and materials scientists that quantum computing hopes to serve.Despite steady progress, today’s quantum computers remain far from tackling the applications they promise. The challenge is scale: performing useful calculations will require machines with millions of quantum bits, or qubits, which are the building blocks of quantum computers. But progressing from devices with hundreds or thousands of qubits to ones with millions exposes a weak point that has long been accounted for via design work-arounds rather than solved—Josephson junctions and more specifically, the materials these critical contraptions are made of.At the heart of today’s most advanced quantum computers sits a device called a Josephson junction. “The Josephson junction is the transistor of quantum computing,” says Kin Chung Fong, an engineer at Northeastern University, Burlington. In simple terms, that term describes what a Josephson junction is—a quantum switch that, like a transistor, turns on and off repeatedly. When fashioned into a special circuit, it enables the circuit to store and manipulate quantum information.Some researchers are now voicing concerns that the materials used by nearly the entire quantum computing industry, including Google and IBM, to build these junctions may not scale to the large, stable machines required for real-world applications. “If you want to make millions of qubits on a single chip,”