Quantum computers are far from being reality.
Researchers are trying to get these qubits into a stable position. Thats the first which has to happen for quantum computers to become 'realistic'.
Afterwards devices with more than just a few of these qubits have to be developed.
[...]
The first step, getting a handful of qubits into a stable position, is already done:
https://newsroom.intel.com/news/intel-advances-quantum-neuromorphic-computing-research/https://www.technologyreview.com/s/610274/google-thinks-its-close-to-quantum-supremacy-heres-what-that-really-means/It's a long shot from production ready quantum computing, but there's a reason why NIST is already working on a new standard recommendation for post-quantum cryptography:
https://csrc.nist.gov/Projects/Post-Quantum-CryptographyIt's not around the corner, but we're well on our way. It is worth noting though that quantum computing is not the magic wand that it is often made out to be.
I highly doubt that quantum computing will even become a problem during
our life time. The advances in terms of processing power of current computers
are already slowing down, because companies like Intel are already having problems
to keep up with Moore's law.
Traditional computing reaching its physical limit is actually one of the reasons why quantum computing is being heavily researched in the first place. Accordingly we can expect more and more funding being poored into R&D for quantum computing (and other approaches such as neuromorphic computing) as improving traditional architectures becomes less and less feasible.
Besides, I read somewhere that a Bitcoin private key is so large that it would take more energy
than is produced by the sun in its lifetime to power a computer that would have
enough computing power to successfully crack it.
That is assuming brute-forcing the private key space of Bitcoin. Quantum computing could make deriving the private key of an address from its public key actually feasible.
You know how Bitcoin is sometimes described as being protected by math? There are math problems at which quantum computing stands to excel compared to traditional computing -- some of which will likely affect asymmetric cryptography as used by Bitcoin.
There are other threats that are a bigger concern to the security of Bitcoin than
quantum computing.
If you are referring to sociopolitical threats -- yes, definitely.