  Quantum technology is maturing to the point where quantum devices, such as
quantum communication systems, quantum random number generators and quantum
simulators, may be built with capabilities exceeding classical computers. A
quantum annealer, in particular, solves hard optimisation problems by evolving
a known initial configuration at non-zero temperature towards the ground state
of a Hamiltonian encoding a given problem. Here, we present results from
experiments on a 108 qubit D-Wave One device based on superconducting flux
qubits. The strong correlations between the device and a simulated quantum
annealer, in contrast with weak correlations between the device and classical
annealing or classical spin dynamics, demonstrate that the device performs
quantum annealing. We find additional evidence for quantum annealing in the
form of small-gap avoided level crossings characterizing the hard problems. To
assess the computational power of the device we compare it to optimised
classical algorithms.
