Entanglement is the idea that in the quantum world, objects are not independent if they have interacted with each other or come into being through the same process. They become linked, or entangled, such that changing one invariably affects the other, no matter how far apart they are - something Einstein called "spooky action at a distance".Entanglement may also provide a nearly uncrackable method of communication. Quantum cryptographers can send "keys" to decode encrypted information using quantum particles. Any attempt to intercept the particles will disturb their quantum state - an interference that could then be detected.
In April 2004, Austrian financial institutions performed the first money transfer encrypted by quantum keys, and in June, the first encrypted computer network with more than two nodes was set up across 10 kilometres in Cambridge, Massachusetts, US.
Quantum computers are another long-term goal. Because quantum particles can exist in multiple states at the same time, they could be used to carry out many calculations at once, factoring a 300-digit number in just seconds compared to the years required by conventional computers.
But particles of matter interact so easily with others that their quantum states are preserved for very short times - just billionths of a second. Photons, on the other hand, maintain their states about a million times longer because they are less prone to interact with each other. But they are also hard to store, as they travel, literally, at the speed of light.
In 2001, scientists managed to stop light in its tracks, overcoming one practical hurdle. And the first quantum logic gate - the brains behind quantum computers - was created with light in 2003.
