Quantum computing: Cheat Sheet

How superpositions and spooky action at a distance could help factor massive numbers...

Time machines - oh, boy!
Steady on Sam, I love science fiction as much as the next geek but I'm not talking about Quantum Leap here. This is even more exciting than time travel.

OK, so what is this quantum computing lark then?
Quantum computing and quantum information processing are research efforts that seek to exploit quantum mechanical phenomena to perform tasks such as massively parallel computing. The quantum research field also encompasses quantum cryptography, which utilises quantum phenomena to guarantee secure communications.

What are these quantum phenomena you talk of?
Tsk! Clearly weren't paying attention in physics class were you?

Quantum mechanics is a branch of physics that describes all manner of weirdness and 'spooky behaviour' - that is, quantum phenomena - taking place at the atomic and sub-atomic levels where electrons, protons and other particles exist.

The quantum world's spooky behaviour, for example, sees matter and energy able to behave both like particles and waves simultaneously, and apparently exist in two places at once.

An atom: quantum computing all you need to know

Quantum mechanics becomes evident at the atomic and sub-atomic levels
(Photo credit: Shutterstock)

My head hurts.
That's to be expected. All of this quantum weirdness is deeply counter-intuitive - if not downright bizarre - to our human brains because it stands in stark contrast to the classical physics we experience in our everyday lives.

Thanks for the physics refresher - but what does all this spooky behaviour have to do with computers?
Good question. Instead of having bits, as a classical computer does, which represent either a one or a zero, a quantum computer has quantum bits - qubits - which can represent zero, one, or a superposition of both - that is, any amount of either zero and one simultaneously. As a result, unlike a traditional computer which can only store one number in a single register at any one time, a quantum computer can store more than one.

Adding more qubits exponentially increases the size of the number that can be stored - a computer with a 100 qubits would be able to store a massive number in its register, for instance.

As well as qubits, another key element of quantum computing is a phenomena known as entanglement.

Hang on, what's quantum entanglement when it's at home?
I was afraid you were going to ask. Quantum entanglement is the point where scientists typically abandon all hope of being understood because the thing being described really does defy the classical logic we're used to.

An object is said to become quantumly entangled when...


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