A crystal is like a perfectly laid mosaic of atoms. But growing such a mosaic is a tricky task: if the order slips even slightly, 'seams' appear — boundaries where rows of atoms don't align. For ordinary electronics, that's a minor issue, but for a quantum computer, it's a disaster. A quantum bit (qubit) stores information in a delicate state that is destroyed by the slightest disorder in the material.
Scientists took a gallium arsenide substrate and grew on it an aluminum film just 10–20 nanometers thick — a thousand times thinner than a human hair. Using molecular-beam epitaxy (a method where atoms are deposited layer by layer, like bricks) they managed to produce an almost perfect crystal. X-rays showed that defective 'seams' are a hundred thousand times fewer than in previous samples. The aluminum atoms stood in line as neatly as soldiers on parade.
Such purity matters because aluminum is a superconductor. When cooled to a few degrees above absolute zero, it conducts electricity without resistance, and qubits based on it can work longer. The fewer defects, the less interference. Previously, it was thought that aluminum on such a substrate would always have defects, but now there is a platform for scalable quantum computers.
The film is 10–20 nanometers thick. If you scaled it up to the thickness of a sheet of paper, a defective 'seam' would be the size of a pinhead, and only one across the entire sheet.
In the series 'Devs', a quantum computer suffers from noise that wrecks computations. Clean superconducting films are precisely an attempt to quiet that noise.