A quantum bit is like a spinning top that must keep spinning steadily for a long time. In germanium, researchers have learned to set such tops spinning, but the floor around them is always trembling: electrical noise knocks the spin off course. To make the floor more even, a thick layer of silicon-germanium is usually placed on top, like a carpet that muffles footsteps.

But if you want to place superconducting components nearby (needed for some quantum tricks), the thick carpet gets in the way: the superconductor must be close. The authors of this new work took a risk and made the carpet very thin — only 4 nanometers, which is five times thinner than usual. To avoid damaging the superconductor with high temperatures during insulation deposition, they developed a low-temperature oxide deposition process.

And here's the result: the noise in quantum dots on the thin carpet turned out to be nearly the same as on the thick one — about 1.8 microelectronvolts per square root of hertz. It's as if the top on the thin carpet spins just as steadily as on the thick one. This means germanium qubits can be combined with superconductors without sacrificing quality.

Such a hybrid opens the door to devices where quantum information is stored in the electron's spin and transmitted through superconducting contacts. The thin carpet is no longer an obstacle.