Quantum computers are already here in a limited form, and fully functional versions are on the way. They will be as transformative for mankind as were the mainframe computers, personal computers, and smartphones that we all use. As do all advancing technologies, they will also create new nightmares. The most worrisome development will be in cryptography.
Within seven years -- about when the iPhone 11 is likely to be released -- the smartphones in our pockets will be as computationally intelligent as we are. It doesn't stop there, though. These devices will continue to advance, exponentially, until they exceed the combined intelligence of the human race.