Glossary
Key terms from all four chapters, with links back to the lessons where each concept is explained.
Qubits & Superposition
- Qubit
- The basic unit of quantum information — like a bit, but can exist in superposition.
- Superposition
- A quantum combination of basis states until measurement collapses the state.
- Measurement
- Extracting a classical 0 or 1 from a qubit, with probabilities set by its amplitudes.
Quantum Gates
- Quantum gate
- An operation that transforms a qubit state on a circuit wire.
- Pauli X
- Bit-flip gate — swaps |0⟩ and |1⟩.
- Pauli Z
- Phase-flip gate — adds a minus sign to the |1⟩ component.
- Hadamard (H)
- Creates equal superposition from |0⟩ or |−⟩ from |1⟩.
Entanglement
- Two-qubit state
- A joint system with four basis states: |00⟩, |01⟩, |10⟩, |11⟩.
- Entanglement
- A joint state that cannot be described by separate qubit values.
- Bell state |Φ+⟩
- An entangled state (|00⟩ + |11⟩) / √2 built with H and CNOT.
- CNOT
- Controlled-NOT gate — flips the target qubit when the control is |1⟩.
Quantum Algorithms
- Oracle
- A black-box gate that encodes problem information into quantum amplitudes.
- Diffuser
- Grover step that reflects amplitudes about their average to amplify the marked state.
- Grover search
- Quantum search algorithm with about √N queries instead of N classically.