This would necessarily be one of the most closely guarded secrets in the world. Whoever has access to QC can immediately break almost any cryptographic scheme (except for one-time pads and quantum cryptography). Of course the government would go to great lengths to protect this monopoly.
I believe this because 1) the N.S.A. has effectively unlimited, off-budget resources at its disposal, 2) the ability of QC to break all public-key cryptographic schemes is not a matter of conjecture; it is only a matter of engineering, and 3) the N.S.A. has recruited and cultivated many--perhaps most--of the brightest minds in the relevant fields.
How could they NOT throw unprecedented resources at this one engineering problem? If they're not there yet, they're far in the lead.
My first thoughts as I read the title. Once this 'cat gets out of the bag,' everyone going to need new encryption schemes.
The combination of quantum computation and nanotechnology makes the mind boggle (as best it can at something it doesn't have the ability to comprehend).
We are in very scary territory the next few decades....
We can only "hope" that the same semi-benovelent attitudes prevail among those who possess this technology as those which prevailed among the controlling interests in the Manhattan Project.
If not...
Hmmm. It looks like we'll be seeing some very long keys being used by those who need/want privacy. Enough RAID 0s (interleaving) in RAID arrays will make that feasible, though.
...time to review a few things. I don't need such encryption, but others will want it.
This would also blow the security off of internet commerce overnight. If the science is near at hand, not just governments are going to be questing for it.