Explainer: what is quantum computing

• Two quantum tribes: Sydney Uni and UNSW, the best of frenemies

Classical computers use binary switches to process calculations. Each "digital bit" is either on or off, a one or a zero. Like a recipe, these switches cumulatively solve problems step by step. By amassing billions of these transistors, modern computers are able to perform calculations and run processes at very high speeds.

However, there are limits to the number of transistors we can physically fit on to a processing chip. Classical computing has boundaries to its operative power.

Artists' impression of binary digits being 'exploded' by a quantum cloud.

Quantum switches, however, are able to be on or off, or a little bit on, a little bit off and/or both at the same time. These quantum bits, or qubits, allow for multiple and parallel computations to occur simultaneously. This provides the operational grunt – crunching huge numbers – that quantum computing promises.

Qubits operate at the nanoscale – a billionth of a metre – and are able to harness the unusual behaviour of matter at this size. 

Nanoscale objects such as electrons, photons or individual atoms, are not quite particles, not quite waves. They operate as a hybrid of both, sometimes more wave-like, sometimes more particle-like. Because they can exist in multiple states at once, used correctly, qubits can process more information and are more powerful switches for computing.

However, the quantum states of qubits are fragile, so scaling them up to a size where quantum computers do useful things is very difficult. This is the next big challenge.

Quantum computers will not replace your laptops. They will be used to solve specific problems that require the processing of very large amounts of data. The world's computing future will be a hybrid system of classical and quantum computing.