Wired published a long extract from Amit Katwala's book Quantum Computing: How It Works and How It Could Change the World — explaining how it's already being put to use to explore some of science's biggest secrets by simulating nature itelf:Comments add:
Some of the world's top scientists are engaged in a frantic race to find new battery technologies that can replace lithium-ion with something cleaner, cheaper and more plentiful. Quantum computers could be their secret weapon... Although we've known all the equations we need to simulate chemistry since the 1930s, we've never had the computing power available to do it...
QCs are _still_ much slower than much cheaper conventional computers if you use the best algorithms for each technology. And that will remain the case for a long time yet, and possibly forever. Hence there is absolutely _nothing_ that QCs are good for at this time, except separating fools from their money. Also note the excessive use of "could" in the article. In this context "could" = "maybe, maybe not, but certainly not anytime soon". ...That's right. Quantum computers have not demonstrated the ability to do practical computations, and will not anytime soon, if ever.
Good, grief the very title Quantum Computing: How It Works and How It Could Change the World tells you it's a work of speculative fiction. In the past it would have been Fusion Power: How It Works and How It Could Change the World or Faster-then-light Travel: How It Works and How It Could Change the World or Telekinesis: How It Works and How It Could Change the World or, if you're that way inclined, Yogic Flying: How It Works and How It Could Change the World. Show me one thing that quantum computing has actually achieved that isn't a specially-crafted artificial problem and that couldn't have been achieved with much less effort with a standard computer.
Google has been similarly overpromising self-driving cars, but that technology has been demonstrated in controlled situations, even if it is not yet ready for the mass market.