You don't build a road by demolishing the neighboring houses: first you lay the asphalt, then you grind away the excess, leaving a smooth surface. That's roughly what physicists in Heidelberg did when they took on the production of Josephson junctions. These are tiny sandwiches of superconductor and insulator through which current flows without resistance. Previously, such contacts were made by lifting off a protective mask, as if you were tearing down buildings to make room for a road. That was slow and left ragged edges.

In the new work, they don't demolish the road; they polish it. Onto a silicon wafer they deposit a three-layer structure: niobium, aluminum with its oxide, and niobium again. On top they pour silicon dioxide, like asphalt, and polish it until the top electrode appears. The pressure during polishing is only 138 millibar, about like a breath of wind on your palm, but that's enough to remove 128 nanometers of silicon dioxide per minute. The result is a smooth surface without ragged edges.

Polishing instead of mask lift-off is like grinding a road rather than demolishing buildings. Previously, to make cross-shaped contacts, you had to lift off the mask, leaving burrs on the edges that spoiled the properties. Now the excess silicon dioxide is ground away without touching the contact itself. This speeds up the process and makes it suitable for multilayer integration of superconducting circuits. The method can already be introduced into the production of SQUIDs and superconducting qubits, where large arrays of uniform contacts are needed.