How superpositions and spooky action at a distance could help factor massive numbers...
...to a quantum computer - one scientist describes it as the fuel powering such a machine.
So how can entanglement be created?
Another great question, albeit one requiring a good head for science. Suffice to say, there are various ways of generating entanglement, just as different particles, atoms or physical facets can be used to act as qubits - such as protons, trapped ions, nuclear spins and so on.
Some objects also entangle more easily than others - photons, for instance, have been relatively easy for scientists to entangle while electrons have posed more of a challenge.
Pairs of entangled electrons can exist in cooled superconductors but in order to make use of them scientists have had to devise ways to separate and extract them from the material. This has been achieved by utilising another quantum phenomena known as quantum tunnelling - whereby a particle is able to defy classical physics and pass (or tunnel) through a high energy barrier - and then deploying tiny components such as nanocrystals or carbon nanotubes to act as gates and ensure the paths of the entangled electrons diverge.
Creating reliable entanglement on demand is crucial to creating a viable quantum computer and one of the problems scientists continue to wrestle with.
OK, these quantum computers need qubits and entanglement to work but what kind of hardware would they be made of?
Quantum computers are a new approach to data processing that exploit quantum mechanical phenomena but there is no agreed single way to build such a machine - scientists are in the process of trying various approaches, so it's difficult to know which will prevail in the long run.
Some of the methods being researched include using ions in traps to act as qubits which are entangled with lasers. Then there's optical systems using photons by targeting lasers on beam-splitters to generate qubits. There are also solid state quantum computing research efforts utilising artificial atoms known as quantum dots, or seeking to harness nuclear magnetic resonance to manifest quantum information. Electron-based systems in low temperature superconductors are another big research effort. There is also interest in the potential of carbon-based nanomaterials such as graphene to house electron-based qubits. And that's by no means an exhaustive list of the ongoing research.
Much effort is being expended on working out which technologies have the most potential to build a scalable quantum computer that also maintains its quantum coherence for long enough to perform the necessary calculations and give up the resulting data.
Since measuring a quantum state collapses it to a classical state then a...