I heard the news that quantum computer is sort of already created but it is still not that powerful. I don't believe scientists can invent such a thing. And even if they do... We can see here http://bitcoin.stackexchange.com/questions/2847/how-long-would-it-take-a-large-computer-to-crack-a-private-key that it would take 0.65 billion billion years for our computers to do so. If quantum computer is 100 000 faster then instead of 6.5*10^17 years it would take 6.5*10^12 which doesn't make much difference.
Unfortunately, it isn't that easy to dismiss. There are two factors: the computational speed and the algorithm.
A quantum computer using a simple brute force algorithm like what might be done on current computers indeed would not be a problem. However, quantum computers are especially suited for using a different algorithm that reduces the computation time by a huge factor.
An analogy
The time to search an unsorted array is described as Θ(n), which means the average number of operations is proportional to the number of items in the array. In contrast, the time to search a sorted array is Θ(log n).
Let's compare times assuming that an operation takes 1 ns (1/1000000000 second).
| Count | Unsorted Ops | Sorted Ops | Time Comparison |
| 10 | 10 | 3 | 10 ns vs. 3 ns |
| 1000 | 1000 | 10 | 1000 ns vs. 10 ns |
| 1 million | 1 million | 20 | 1000000 ns vs. 20 ns |
| 1012 | 1012 | 40 | 1000 second vs. 0.000000040 seconds |
| 2128 | 2128 | 128 | 1020 centuries vs. 0.000000128 seconds |
The algorithm makes all the difference in the world. Please note that the times are not actual times, and there is quite a bit of hand waving.
In the end, as panju1 and DooMAD noted, a solution is to switch to a "quantum-resistant" cryptography. However, quantum-resistant cryptography is still being developed, and the danger is that quantum computers will be able to break current cryptography (including Bitcoin) before quantum-resistant cryptography can be developed.
