The Quantum Computer Puzzle

Q uantum computers are hypothetical devices, based on quantum physics, which would enable us to perform certain computations hundreds of orders ofmagnitude faster than digital computers. This feature is coined “quantum supremacy”, and one aspect or another of such quantum computational supremacy might be seen by experiments in the near future: by implementing quantum error-correction or by systems of noninteracting bosons or by exotic new phases of matter called anyons or by quantum annealing, or in various other ways. We concentrate in this paper on the model of a universal quantum computer that allows the full computational potential for quantum systems, and on the restricted model, called “BosonSampling”, based on noninteracting bosons. A main reason for concern regarding the feasibility of quantum computers is that quantum systems are inherently noisy. We will describe an optimistic hypothesis regarding quantum noise that will allow quantum computing and a pessimistic hypothesis that won’t. The