START HERE: WHAT IS A BIT?

A bit is the smallest piece of information

Bit Short for binary digit: a single 0 or 1.

In hardware Stored as a transistor switched on or off, a voltage, or a tiny magnet pointing one way or the other.

Bytes and beyond 8 bits make a byte. Photos, songs and apps are just long lists of bits.

Every computer you've used, from a calculator to a supercomputer, works with bits.

WHAT IS QUANTUM PHYSICS?

The rules of the very small

Quantum physics The branch of physics that describes atoms, electrons and particles of light (photons).

Discovered In the early 1900s, by Planck, Einstein, Bohr, Schrödinger, Heisenberg and others.

Where it shows In tiny things, and in carefully isolated, very cold systems. Big, warm objects average it away.

Everyday physics is a very good approximation; quantum physics is what's really going on underneath.

QUANTUM IDEA 1

Quanta At the atomic scale, energy comes in fixed steps, not any amount.

Photons Light comes in packets with energy E = hf.

For qubits Two neighbouring energy steps become the qubit's 0 and 1.

The word 'quantum' just means 'a fixed amount'.

QUANTUM IDEA 2

Wave-like Single electrons build up an interference pattern, as if each went through both slits.

Probabilities Quantum physics predicts the odds of each result, not one certain outcome.

Measurement matters Checking which slit an electron used destroys the pattern.

Superposition, probability and measurement: the same three ideas run every quantum computer.

SO WHAT IS A QUBIT?

Qubit Short for quantum bit: any quantum system with two states we call 0 and 1.

The difference A bit is always 0 or 1. A qubit can be in a blend of both (a superposition) until it is measured.

Real qubits Two energy levels of an atom, the spin of one electron, or the two lowest energies of a tiny superconducting circuit.

Now you have the vocabulary. Next: why anyone would build a computer out of qubits.

UNIT 1 STUDY COMPLETE

💡

You can define a bit, explain what quantum physics is, and say what makes a qubit different from a bit.