As suggested, these quantum computing circuits will be well suited to certain applications providing great advantages over traditional circuits, but they won't work for everything. I think the key to this advancement is that being able to produce them on silicon will allow traditional circuits to be used in conjuction with the quantum circuits to provide complete systems. It's the combination that will make it all work.
Something to keep in mind about the ability of quantum computers to crack encryption codes that are currently used, is that all mainstream commercial software and hardware that uses any encryption, uses relatively weak encryption by professional standards.
It is more likely that early quantum computers (which will still be very expensive) will be used to rapidly crack widely used codes, rendering web commerce (for example) vulnerable. The companies will respond by increasing key lengths and security standards, then they will be cracked again with more time and effort, in an arms race scenario. This is how bugs and flaws in current encryption are found.
The military, spy agencies and some financial institutions will put a premium on security, and are already buying quantum encryption systems that are for sale for the last few years. But these systems have limited range (100-200 km), and only work on dedicated optical fibres, so they will not be the basis of a widespread consumer technology.
I will be very curious to watch for developments applying quantum encryption ideas to wireless communications (research mentioned in the article sponsored by Nokia).
I think you make a good point about a quick transition.
But one thing stressed to me by Mark Thompson is that quantum computing will be good at doing some things that would be practically impossible for conventional computers.....but that quantum computing will not necessarily displace conventional electronics for some of the tasks it already does.
It is not the case the quantum computing is the same as electronic computing but faster.
And there is for example already the scope for non-quantum photonic computing (using a lens as a highly parallel mathematical transform) which is now rarely used.
"Quantum computers pose a threat to secure systems as they could crack all existing secure systems," says O'Brien, adding "but they would also provide the solution."
The ramifications are clear, I think. As soon as just a few of these quantum computers come online, all conventional PC's become 100% vulnerable, and so an extremely fast technology transition is to be expected. More like a "flip" than a transition, in fact. Engineers describe this as positive feedback; marketing people as "high adoption rate". Quantum computers represent the very definition of a disruptive technology, and their very presence in the marketplace ensures rapid take-up, and the rapid obsolescence of conventional PC's - not just because of this security issue, but also because quantum computers will be way faster.