ARTICLE: E&T MAGAZINE – Quantum for dummies: the basics explained

Professor Alan Woodward from the University of Surrey attempts to demystify the quantum world by explaining key terminology and theory.

Which atoms and particles does quantum physics apply to?

Every particle, atom and molecule [photons, electrons or whole atoms] behave in accordance with the laws of quantum mechanics – as does everything. However, this only becomes important when broken down to the atomic, sub-atomic and molecular scales. Quantum mechanics is trying to use the physics of things at the atomic level to create effects in the macroscopic world – which is our world.

What is superposition?

Superposition is a system that has two different states that can define it and it’s possible for it to exist in both. For example, in physical terms, an electron has two possible quantum states: spin up and spin down. When an electron is in superposition, it is both up and down at once – it is a complex combination of both. Only when it is measured does it drop out of superposition and adopt one position or the other. If you build algorithms in the right way, it’s possible to effectively harness the power of that superposition.

What is a qubit?

A qubit is a quantum bit that is the basic unit of information in a quantum computer. It has something – a particle or an electron, for example – that adopts two possible states, and while it is in superposition the quantum computer and specially built algorithms harness the power of both these states.

Why is it tricky to store information in quantum computers?

Particles in superposition is the main way to store information in quantum computers.

However, storing a quantum state – i.e. particles in superposition – is very difficult. Any interaction with the universe will disrupt it and cause errors. This is why quantum computers are shielded electro­magnetically and cooled down to almost absolute zero.