D-Wave

D-Wave's machines are quantum annealers, not universal quantum computers. They solve one kind of problem: finding the lowest energy of a system encoded to represent an optimisation problem. They cannot run Shor's algorithm, and their qubit count — several thousand — is not comparable to the hundreds on gate-based machines.

The debate has been about whether the machines genuinely exploit quantum effects in a way that beats classical methods. Quantum effects have been demonstrated, but unambiguous speedups against well-written classical algorithms have been hard to establish.