Re: 6,681 qubits?
Spontaneous collapse of the quantum state to a classical state is indeed a major problem for quantum computing. And the problem increases not only with the number of entangled qubits, but also with the number of operations performed on these. And to crack codes with longer keys, you not only need more qubits, you also need more operations on each.
The simple way to avoid quantum computers cracking your code is just to increase the key length -- if 256 bit keys become crackable in 10 years (which I doubt), you just go to 1024 bit key length, and you will be safe for another decade or more. Unless some giant breakthrough is made that will make quantum computers scale easily, and I seriously doubt that.
That doesn't mean that quantum computers are pointless. They can be used for things such as simulating quantum systems and for quantum annealing. But forget about cracking codes or speeding up general computation. You are better off with massively parallel classical computers, and to avoid huge power bills, you should probably invest in reversible logic, which can avoid the Landauer limit (a thermodynamic lower bound on the energy cost of irreversible logic operations).
Biting the hand that feeds IT
