The tech: The core concept of quantum computing has been on the drawing board for decades now: exploiting the behavior of matter at the subatomic level to create a computer that solves problems exponentially faster. Google, Microsoft, Amazon, and IBM have all thrown money at it, while the NSA wants to use it to render current-generation encryption obsolete.
The timeframe: Depending on whom you ask, quantum computing's already arrived. One firm, D-Wave, has been marketing its quantum-computing product to Google, NASA, and Lockheed-Martin, with list prices in the millions of dollars. But controversy remains as to whether D-Wave's products provide real improvements over a regular computer, and we've yet to see a truly earth-shaking application of quantum computing in the real world.