But realizing that promise means, among other things, cracking a thorny paradox. A basic operation of any computer is checking for mistakes. But by the logic of quantum computing, the act of checking is itself likely to create an error.

Researchers at Google have been trying to solve this problem, and now they believe they've made some progress. What you see above you is a tiny piece of aluminum film on a sapphire wafer built by the Google team. The nine miniaturized fire hose nozzle-type devices in the middle of the chip house quantum bits, or qubits—quantum computing's more elaborate answer to the 1s and 0s of traditional microprocessors. The researchers say they've devised a sneaky technique for some of the qubits to check out their neighbors for errors without injecting new mistakes themselves.