Making quantum computers reliable

CALCULATING machines that run on quantum bits (known as qubits, for short) are, by some accounts, the future of computation. Quantum computers have the theoretical advantage that they can solve with ease certain mathematical problems, such as the factorisation of large numbers, which are hard or impossible for classical machines. This is possible thanks to a qubit's ability to remain, through the peculiarities of quantum mechanics, in many quantum states simultaneously. The more qubits a compute...