The idea of using quantum mechanics, the laws that govern all fundamental particles in the universe, to process information has revolutionized the theory of computing. And soon, nearly half of a century after its first proposal, a practical quantum computer may finally be built. Quantum machines may soon be capable of performing calculations in chemistry, physics, and other fields that are extremely difficult or even impossible for today’s conventional computers. Yet a significant gap exists between the theory of quantum algorithms and the devices that will support them. Architects and systems researchers are needed to fill this gap, designing machines and software tools that will efficiently map quantum applications to the constraints of real physical machines.