The generally-excellent Ars Technica wins the prize for the single best line about D-Wave’s supposed quantum computer:
D-Wave Systems has presented us with the perfect quantum conundrum. On Tuesday and Thursday, they presented their 16-qubit adiabatic quantum computer to the world. However, details were scarce, leaving us in the superposition of both believing and disbelieving their claims.
Their article on D-Wave’s "demonstration" is also more substantive than what I’ve seen elsewhere:
Jumping off the fence, we will say that we think D-Wave demonstrated a real device; however, we think their device is going to set off a debate in the physics community over where the boundary between classical and quantum computation is. At present, quantum computers are "globally phase coherent," which means that every qubit’s state is entangled (and therefore correlated) with every other qubit. It was this assumption that allowed Grover to show that quantum computers would outperform classical computers in unstructured searches.
The D-wave system, however, is certainly not globally phase coherent, which raises the question of whether it is a quantum computer. Furthermore, they have not even demonstrated that the directly coupled qubits are entangled, or even enter superposition states.
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