I've had a difficult time getting a real answer on this, an the HN crowd seems pretty well-educated, so I'll pose the question here: Do we even have a high degree of certainty that quantum computing is possible? I thought that Bohmian Mechanics was still on the table as possible description of the physical world.
Bohmiian mechanics is a non-local hidden variable theory of Quantum Mechanics. Any result from traditional QM should hold with Bohmian Mechanics, including the ability to perform quantum computations. We have a reasonable certainty that QM is possible thanks to a Threshold Thereom http://arxiv.org/abs/quant-ph/9702029. Additionally, it is quite easy to run algorithms with a small amount of qubits (5-10) that show that theory holds and should continue to hold as more qubits are added. It has become a scaling problem, which hopefully can be solved with time.
We've run very tiny quantum programs already, such as factoring 15 into 3 and 5, but it's been difficult to scale this upwards and work on larger numbers of bits at a time.
So, possible? Yes, for sure. Practical.... Not quite yet, maybe never, maybe soon.
We don't see why it's not possible, we're just not sure exactly what it's gonna look like. Martinis believes it's gonna be surface codes. My group believes it's gonna be cat codes. Or something. Who knows? It's a hugely difficult experimental physics problem, math problem, and engineering problem all balled up into one. Really cool time to be in this field.
And nobody I know really cares about bohmian mechanics. Only outsiders seem to since it seems edgy. I have some philosophical objections to it as well.
It sounds very cool. I'm just trying to figure whether it's exciting in the way the computer engineering was in 1980, or if it's more like the way fusion energy was in 1960.
There is certainly no consensus among physicists that QC is possible. But I think at this point it is more about reducing the cost of a real implementation down to something manageable. (Ie. current schemes would be 10s of billions of dollars+ to build.)
And as for Bohmian Mechanics, I think this is just a re-interpretation of quantum physics, and not actually a competing theory.
If QC is not possible for some new underlying principles (not lack of engineering capability) then it would mean our understanding of QM is fundamentally wrong. This could be the case (we've been wrong in physics many times) even though QM has been verified to more digits of precision than any other physical theory.
Trying to build computers in this case and diagnosing the errors then are likely to give us the data necessary for the discovery of the new, better theory.
Now, if it is possible in principle but not practical to engineer - that's what we need a golden age of engineering research to find out.
