What will quantum computers be able to do that ordinary computers can't do?

What's stopping us from building useful quantum computers? And how long until we'll have them?

Researchers from the University of Maryland have devised a new kind of random number generator that is cryptographically secure, inherently private and — most importantly — certified random by the laws of physics. Randomness is important, particularly in the age of the Internet, because it guarantees security. Valuable data and messages can be encrypted using long strings of random numbers to act as "keys", which encode and decode the information. Randomness implies unpredictability, so if the key is truly random, it's next to impossible for an outsider to guess it.

In the second of two articles, Artur Ekert visits the strange subatomic world and investigates the possibility of unbreakable quantum cryptography.