Quantum computing, if we ever master the science and technology, would usher in a dramatic change in the way computers affect our lives. The most noticeable difference would be in security since in the 90s it was shown that a quantum computer could quickly crack the codes we currently use. Today's encryption schemes rely on being able to do a math problem like factoring the product of two huge prime numbers (only divisible by itself and 1), which would take ages to complete by brute force guessing at all the possibilities. For example, factor 15 into two prime numbers. Easy, 3 x 5. OK, smarty, now factor 136399037. Since it's a product of two primes, there's only one way to make it (if you're curious, it's 11681 x 11677).

The main difference in quantum computing is in how information is stored and transferred. Today's computers use binary – a series of ones and zeroes – to do this. A bit of information (literally a bit) is either on or off, or to the electronics, either there’s a voltage or there’s not. In a quantum computer, a bit not only has two states, on and off, but also a funky, non-intuitive, hybrid on/off state that’s a combination of on and off. Like the infamous Schroedinger’s cat, which was both alive and dead, a QC can store information in three states, on, off, or both! Having 3 instead of 2 states available, a QC is much more versatile and would in essence seem lightning fast next to a regular computer.

To learn more, try this web search result, or book search result. I also really enjoyed Brian Hayes' article in American Scientist, The Square Root of NOT.