yes, quantum computers can do calculations, but my understanding is they have issues with getting exact answers all the time. but what they can do, they do at a lower wattage compared to a standard computer.
improving the error correction and increasing the number of bits is the challenge.
there is already machines that can break smaller codes than bitcoin that use qbits but it's an open question how well they can decrease the error rate (they may not be able to, ultimately, because their physics model may be incorrect). this also doesn't change the fact that there are supercomputers now that potentially could reverse a pubkey -> secret in only a few years, at an extremely high energy cost, and would compete with scientific use of these machines.