Classical bits vs qubits
Every device you use today runs on classical bits — clean, definite 0s and 1s. A qubit lives by different rules: it can hold a blend of possibilities until we look.
Learning objectives
- Distinguish a classical bit from a qubit.
- Describe why qubits enable new kinds of computation.
Classical bits
A bit is like a light switch: always on (1) or off (0). Billions of these switches, flipping fast, power your phone, laptop, and the internet.
Qubits
A qubit is a physical system — an atom, photon, or superconducting loop — whose state can be a controlled combination of 0 and 1. That combination is called a superposition.
Why it matters
With N qubits in superposition, a quantum computer can explore 2^N possibilities in parallel. This does not mean 'faster at everything' — quantum computers help most on very specific problems.
Key terms
Bit
A classical unit of information — 0 or 1.
Qubit
A quantum unit of information that can be in superposition of 0 and 1.
Superposition
A weighted combination of basis states.
Worked example
If a coin is a bit, it lands heads or tails. If it were a qubit, it could 'spin' as a mix of both, until we measure it and force one outcome.
Checkpoint
Which statement best describes a qubit?