At the risk of being off-topic, what exactly is quantum computing and how does it affect bitcoins?
Classical computing first. We're using classical computers.
Binary dig
its (i.e. "
bits") to represent data and code, and logic gates for the calculating parts. The binary digits are generated by a signal generator controlled by a digital clock. When the voltage in the circuit is above a certain threshold, the components are designed to detect that signal as a "1". When the voltage is zero, the components are designed to detect that signal as a "0". The logic gates use these 1's and 0's for calculations, and the calculations can be used to draw to the screen, accept input from mouse or keyboard, play games etc.
Quantum computing is entirely different. Instead of each unit of computation being binary (i.e. only 2 possible states), the units instead have an infinite number of states. This puts their computing power in a completely different league to the Von Neumann binary computers we know today. Binary arithmetic is very limiting; only addition can really be performed directly. To achieve subtraction, multiplication or division in binary computers, some unnatural seeming maths needs to be used. This is perfectly accurate, but involves many more steps than seems necessary to a human observing how it's done (but all those steps are necessary).
With the infinite number base that Quantum Computing could provide, bizarre seeming workarounds are unnecessary. And the sort of massively parallel problems that cryptography poses (i.e. Bitcoin's cryptographically immutable blockchain) could be solved with a tiny fraction of the server farm effort that binary computing would use to crack it. The problem for making QC a non-laboratory reality is this: quantum computing units (qubits as opposed to bits) must be composed of a single atom or atom scale particle. The various sub-atomic particles that make up a qubit are where all the quantum effects to compute with come from. In order to get even a very basic setup running, you really need that laboratory. All quantum computers have been lab based experiments, and I'm not aware of any example that (yet) outperforms binary computers for the same task. And to achieve something that impressive, it's an expensive setup (for which your local tyrants will want you to seek permission or a license).
So in short, they're astoundingly powerful computers that would take what's possible with computing to a whole other level. Once they get out of the "...in 10 years" pipedream stage, that seems to go on forever.