Quantum computers

With basic information processing units (qubits) governed by the exotic phenomena of quantum mechanics, quantum computers have the potential to be far better at performing certain calculations than today's computers using conventional 'bits'. That said, it's far from clear what technology practical quantum computers — if and when they arrive — will use. In an extensive review, six researchers from major labs in the field describe the latest work on the hardware for quantum information systems. Current materials are compared — including the nuclear spins of donor atoms in doped silicon, electron spins in gallium arsenide and nitrogen-vacancy centres in diamond — and the materials that are yet to come are speculated upon. Over the past several decades, quantum information science has emerged to seek answers to the question: can we gain some advantage by storing, transmitting and processing information encoded in systems that exhibit unique quantum properties? Today it is understood that the answer is yes, and many research groups around the world are working towards the highly ambitious technological goal of building a quantum computer, which would dramatically improve computational power for particular tasks. A number of physical systems, spanning much of modern physics, are being developed for quantum computation. However, it remains unclear which technology, if any, will ultimately prove successful. Here we describe the latest developments for each of the leading approaches and explain the major challenges for the future.