Right now there seems to be a lot of buzz on quatum computers. I can read success stories everywhere. E.g. IBM claims the first 5 Qubit processor available in the cloud, D-Wave claims a 1024 Qubit quantum computer so on, others claim n Qubits entangled and so on.

However so far we have no reasonable sized general purpose quantum computer and there seems to be agreement from the experts that it will still take a while till we get there. Some are even questioning if they will be achievable at all.

I am not a physicist. I wonder if there is any roadmap. That is: is there a list of technologies, the open challenges (per technology) and the projected timelines when the challenges might be overcome? Or at least a list of the known challenges and in which order they must be attacked? The only roadmap that I found on the internet was outdated (and predicted that we should have had one for some years already).

To be more specific of what I am after. Suppose I truncate MD5 hashes to the first 64 bits and call this function $H$. According to theory: given a 64 bit $y$ I should be able to leverage a general purpose quantum computer to find an $x$ by brute force in $O(2^{32})$ evaluations of $H$ such that $H(x) = y$.

What would be a roadmap to achieve this on a real hardware in a laboratory? Of course more qubits, sufficient coherence times and so on. But what exactly is missing and how hard do we assume this to be with our current knowledge? How far out is something like this and why? Where could I find either a roadmap or a somewhat comprehensive list of the known challenges?

  • $\begingroup$ Might be of interest www-03.ibm.com/press/us/en/pressrelease/51740.wss $\endgroup$ – user126422 Mar 23 '17 at 17:53
  • $\begingroup$ I knew this already. I would consider this "buzz". I am searching for something that is more on the technical side. $\endgroup$ – Udo Klein Mar 24 '17 at 13:16
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    $\begingroup$ arxiv.org/abs/1510.01406 $\endgroup$ – Craig Gidney Mar 25 '17 at 12:26
  • $\begingroup$ Great, this is the kind of stuff I am searching for. Thanks! $\endgroup$ – Udo Klein Mar 26 '17 at 13:37

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