Quantum Superposition
The ability of a quantum system to exist in multiple states simultaneously until it is measured, at which point it collapses to a single definite state.
Quantum superposition is the principle that a quantum system can exist in multiple distinct states at the same time. A qubit in superposition is simultaneously 0 and 1, not in an unknown state, but genuinely in both states at once, with a specific probability amplitude for each.
When the qubit is measured, the superposition collapses to a single definite outcome: either 0 or 1. The probability of each outcome is determined by the quantum state before measurement.
Superposition enables quantum parallelism: a quantum computer with n qubits can represent 2^n states simultaneously. This does not mean it can check all states in parallel for every problem, but it enables specific algorithmic speedups for problems with particular mathematical structure.