In 1981 the physicist Richard Feynman speculated about the possibility of “tiny computers obeying quantum mechanical laws.” He suggested that such a quantum computer might be the best way to simulate real-world quantum systems, a challenge that today is largely beyond the calculating power of even the fastest supercomputers. ... Recent progress has renewed enthusiasm for finding avenues to build significantly more powerful quantum computers. Laboratory efforts in the United States and in Europe are under way using a number of technologies.