View source for Quantum computing is far away

Some experts predict it will be a problem for Bitcoin’s digital signatures within the decade. Even pessimistic estimates put ‘Y2Q’ at around 30 years away.

* The process of quantum-proofing Bitcoin will take years. Active users will need ample time to move their funds.
* Several years before the Bitcoin-cracking quantum computer actually exists, a time will come when we are no longer sure that it does not. At that point, Bitcoin’s security can no longer be trusted, and it’s already too late.
* Those who bet against science and technological progress almost always end up on the wrong side of history.

Who says it will take decades or years? Is there any credible source that will guarantee you it will take years? And I’m not talking about an explanation how hard it is and concluding that it’s impossible for the next decade. I’m talking about anyone who will publicly give you the guarantee that you can come claim your money if a quantum computer might get sufficient power faster than that?