This computer, called the D-Wave, carries a $10 million price tag, and the idea is that it can perform certain tasks exponentially faster than computers built according to the laws of classical physics—the physics of the everyday world.

The trouble is that even top quantum computing researchers can't quite tell whether the D-Wave will provide this exponential leap when applied to tasks that are actually useful, that can improve how the everyday world operates, that are more than experiments in a lab. But after several months with its D-Wave computer, Google believes that this machine can prove quite useful indeed.

In the future, says Hartmut Neven, who oversees Google's experiments with the D-Wave, it may significantly improve machine learning, the technique by which computers analyze vast troves of data to learn skills like recognizing photos, identifying spoken words, understanding natural language, and, maybe one day, mimicking common sense.