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Comment by arcticbull | Hacker News Reader

I took some courses on quantum computing in college, and my takeaway at the time was all modern approaches to quantum computing are slower (effectively, and worse in almost every case in terms of algorithmic complexity) than their classical counterparts. Are we any closer to getting a quantum implementation of Shor's algorithm? My understanding is that none of D-wave's systems for instance are anywhere close to implementing Shor, and I treat that as my "are we there yet" test. I really enjoyed the classes, but haven't kept up with advancements in the space in really any way.

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> My understanding is that none of D-wave's systems for instance are anywhere close to implementing Shor, and I treat that as my "are we there yet" test.

Do you care about the algorithm, or the result? Currently we can factor 11-bit semiprimes fairly reliably, and our hardware is capable of running 16-bit problems. But no, it's not Shor's algorithm. It's conceptually much simpler: implement a multiplication circuit, clamp the output, anneal to find the inputs. Despite not being Shor's algorithm, we've yet to see a competitor demonstrate anything close on the factoring problem.

There's a strange thing in quantum computing happening right now. Certain people believe that there's only one kind of quantum computing, because it's got a provable speedup under yet-unobtainable assumptions. Adiabatic quantum computing, under a similarly unobtainable set of assumptions, can run the same algorithms, polynomially equivalent in time and space. But gate-model gets all the hype.

And speaking of hype, 2017 just called. https://spectrum.ieee.org/computing/hardware/google-plans-to...

I mostly care about the available time for Bitcoin to switch to quantum secure cryptography. It’s scary that people wouldn’t accept a 10x fee increase which would be necessary for the switch.

It's already too late. Even if they switched now it wouldn't save all the coins stored in older addresses.

They need to choose between removing a large part of the coins from the blockchain or accepting that those coins will be taken by whoever has the technology first. Both options are bad for bitcoin.

It'a not that bad, it's easy to add a new digital signature to Bitcoin (the hard part is developing one that's accepted by the community). Most of the money can be consolidated to less UTXOs. The problem will still be that we have no idea when the current signatures get unsecure.

Are there any resources you can recommend to understand D-wave's quantum computing a bit better?

I took a very basic course about gate-model quantum computing at my university. The (mathematics) professor would have loved to be able to explain adiabatic quantum computing on a basic level, but was unable to find entry-level material to really understand how it works or what problems it can solve.

It doesn't matter if classical solutions are better at this point. We need to make progress and any baby step helps.

According to some sceptics it does matter. Some are saying that error rate will grow the same way as “computational power” ie. you can’t physically get value out of quantum computing and it will never outperform classical computer. I’m not saying that is the case but the argument is sound and until proven otherwise we won’t know.

Error rate remains more or less proportional with qubit growth as long as companies optimize for qubit growth alone. But once you have thousands of qubits you can use that to build something like a few dozen error-free logical qubits. Most companies don't believe it's worth attempting that yet and that it's better to optimize for qubit growth for now.

I think that's what they are arguing with - if you increase number of entangled qubits - your error rate will explode the same way that your "computational potential". If that's the case then the whole quantum computing has a huge problem, you'd have to cool it down closer and closer to absolute zero. Having more machines that do poor calculation won't help here - you'll end up with a farm of expensive fridges. Just for the record - I want this to be false, quantum computing will hopefully work.

Expecting D-wave to get shor working on its quantum computer is like expecting Nvidia to run Windows on its gpus. D-wave isn't even attempting to solve problems like the shor algorithm.

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