[vsef]

An explanation in comic form with text by quantum computing researcher Scott Aaronson: https://www.smbc-comics.com/comic/the-talk-3

QC is about setting up interference patterns between the qbits, it is fundamentally unlike classical computing. For some problems algorithms can be designed that use those interferences to compute things, like the famous Shor's algorithm for polynomial time prime factoring.

QC speeds things up only in the cases where an asymptotically faster algorithm can be designed this way, it is not a general purpose parallelization mechanism.

And we don't know many things it speeds up for sure! For example: we don't actually know that there isn't a classical polynomial time prime factors algorithm we haven't found. Here is a recent example of a quantum algorithm leading to the discovery of a classical algorithm that is equivalent to the quantum: https://www.quantamagazine.org/teenager-finds-classical-alte...