Scientists have long dreamed of developing quantum computers, machines that rely on arcane laws of physics to perform tasks far beyond the capability of today’s strongest supercomputers. In theory such a machine could create mathematical models too complex for standard computers, vastly extending the range and accuracy of weather forecasts and financial market predictions, among other things. They could simulate physical processes such as photosynthesis, opening new frontiers in green energy. Quantum computing could also jolt artificial intelligence to a vastly higher level of sophistication: If IBM’s Watson can already win at Jeopardy! and make some medical diagnoses, imagine what an enormously smarter version could do.