Superposition

Superposition is one of the core principles of quantum mechanics. A qubit in superposition is described by a linear combination of the basis states |0⟩ and |1⟩: |ψ⟩ = α|0⟩ + β|1⟩, where α and β are complex probability amplitudes satisfying |α|² + |β|² = 1. The Hadamard gate is the most common way to put a qubit into equal superposition from the |0⟩ state, resulting in |+⟩ = (|0⟩ + |1⟩)/√2 — a 50/50 probability of measuring 0 or 1. Superposition enables quantum parallelism: a quantum circuit operating on n qubits in superposition effectively processes 2ⁿ inputs simultaneously. However, measurement collapses the superposition, so extracting useful results requires careful algorithm design using interference.