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D-Wave Quantum Computing Solution Raises More Questions
benonemusic writes "The commercially available D-Wave computer has demonstrated its ability to perform increasingly complex tasks. But is it a real quantum computer? A new round of research continues the debate over how much its calculations owe to exotic quantum-physics phenomena. 'One side argues there is too much noise in the D-Wave system, which prevents consistent entanglement. But in an adiabatic device, certain types of entanglement are not as vital as they are in the traditional model of a quantum computer. Some researchers are attempting to solve this conundrum by proving the presence or absence of entanglement. If they show entanglement is absent, that would be the end of the discussion. On the other hand, even if some of D-Wave's qubits are entangled, this doesn't mean the device is taking advantage of it. Another way to prove D-Wave's quantumness would be to confirm it is indeed performing quantum, and not classical, annealing. Lidar has published work to this effect, but that triggered opposition, and then a counter-point. The debate continues.'"
how do you show the presence of entanglement without disturbing it?
Can someone explain to me how this chip could be calculating anything unless the quantum part was working?
D-wave is very secretive about how their machine operates and do not respond to academics who want to know exactly how it works -- this is the source of much of the speculation. On top of that you need to specially code your instructions for it, because it can only do a subset of what a general quantum computer could in theory do.
The D-Wave engine can indeed solve some specific optimisation problems by a method called adiabatic annealing. Essentially this done by encoding the problem to be solved in some initial state of the physical components of the engine, and letting it evolve without exchanging energy with the outside world (this is what adiabatic means). The evolution is done in such a way that the solution to the optimisation problem eventually appears (this is the annealing part) with some probability.
The engine definitely works, this is not disputed. However there is some debate whether the way the engine works is essentially classical or essentially quantum. At the moment the engine is not especially powerful and it is very noisy, so there is no easy way to tell. In the 3 papers cited in the Fine Article, one says this is definitely quantum because the way the system evolves does not match the way classical annealing is simulated (simulated annealing (SA) is a very popular way to solve some complex classical optimisation problems). The second paper says that it is still possible to achieve the signature observed in the first paper by purely classical means, so this is not so clear. The third papers says that this is correct, but that there is more to the signature than was reported in the first paper, and that *this* is more likely to be quantum than not.
Feel free to contradict me. At any rate, and this is not disputed, the D-Wave engine does not work in the way quantum computers are expected to work in the literature about this topic. It would not be useful to solve factorisation problems as in the Shor algorithm. Rather, it would be useful to solve some optimisation problems in a faster way than with classical or traditional CPUs or GPU. This is still very useful, although at the moment the D-Wave computer's inner working are mostly secret, not hugely fast, and noisy. So D-Wave's qbits are a bit of a misnomer. They should be called something different so as not to engender confusion, perhaps obits (optimisation bits)?
I hope this make sense to you.
Answer: It's *SO* quantum that even the issue of whether or not it's quantum exists in a superposition of states!