Guys stop worrying about Quantum Computers. While there are
scientific tasks they can do faster than a normal
computer, a quantum computer can be much dumber than your grandmother's laptop that she has purchased in 2007.
No, QUANTUM COMPUTERS WILL NOT DISRUPT BITCOIN.
Bitcoin has built in quantum resistance.
Quantum Computers will still be slow. The only problem would be public key cryptography
which is not secure against quantum computers, however Bitcoin promises to implement
a new public-key algorithm which tackles this issue.
I recommend you this PDF:
The Limits of Quantum Computers by Scott Aaronson