Seth has suggested experiments that Dwave can perform to prove if their system is achieving a quantum state.
The pioneers of superconducting quantum computation had been able to demonstrate the quantum nature of their devices by zapping them with fast microwave pulses and looking at their responses. But those devices weren't adiabatic; they operated at speeds comparable to those of a conventional computer. The D-Wave device, by contrast, is purposefully slow: therefore, no zapping is possible. As a result, there are a limited number of experiments that can indicate whether the device is really doing quantum computation. One, however, is to vary the slowness with which the device oozes from its initial state to its final state. Halfway through the oozing process, the computer arrives at a point where it must start making the hard choices that lead to the problem's solution. Here the computer is in a weird quantum state, in which every bit registers 0 and 1 at the same time. I urged the D-Wave researchers to explore this critical point and search for the telltale signs.
More recently, I [Seth Lloyd] spoke with Herb Martin, the CEO of D-Wave, and Geordie Rose, the company's chief technology officer and cofounder, and emphasized the need for them to pursue these experiments if they are truly interested in explaining how their devices work. One experiment that I [Seth Lloyd] recommended to Rose is a specific protocol for creating and verifying the presence of a so-called Schrödinger's-cat state, a specific instance of the state in which all the qubits register both 0 and 1 simultaneously
Scott Aaronson also has a short article with his views.