A $100,000 offer is being made by quantum computing/complexity theory researcher Scott Aaronson to whomever can disprove the possibility of scalable quantum computation.
Although very primitive, small-scale quantum computers have been developed and realized in the field, the question of whether or not a large-scale quantum computer can exist to handle arbitrarily large computations is the focus of ongoing research and a matter of debate (at least to some researchers).
This is ultimately a matter of the possibility of quantum computers being able to exist in principle according to the laws of physics, and not one of just theoretical and technological advancement in a given period of time.
The way I see it is that any legitimate attempts to actually disprove the possibility of large scale quantum computation will only end up revealing more details and reasons to believe that large scale quantum computers can and will exist. I would even be willing to go as far as saying that the existence of large scale quantum computation ought to be demanded by the idea of computational universality.