Definition

The basic unit of quantum information. Unlike a classical bit (0 or 1), a qubit can exist in a superposition of both |0⟩ and |1⟩ states simultaneously, enabling quantum parallelism.

Examples

• • A classical bit is like a coin lying flat (heads or tails). A qubit is like a spinning coin — both outcomes exist simultaneously until observed.
• • Two qubits can represent 4 states at once, three qubits 8 states, and n qubits 2ⁿ states simultaneously.

Visual

Bloch sphere visualization: a 3D sphere where the north pole is |0⟩, the south pole is |1⟩, and any point on the surface represents a valid qubit state.

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