- Amplitude
- A complex number associated with a basis state. Its squared magnitude contributes to the probability of observing that state.
- Annealing
- An optimization approach that searches for low-energy configurations; quantum annealing uses quantum effects in a specialized model.
- Ansatz
- A parameterized circuit structure chosen as a candidate family of quantum states in a variational algorithm.
- Backend
- A simulator or physical quantum device targeted for execution.
- Basis state
- A reference state used to express a quantum state, such as the computational basis states |0〉 and |1〉.
- Bell state
- A maximally entangled two-qubit state used in demonstrations, communication protocols, and tests of quantum correlations.
- Bloch sphere
- A geometric representation of a single pure qubit state.
- CNOT
- A controlled-NOT gate that flips a target qubit when the control is in the |1〉 computational basis state.
- Circuit depth
- A measure of how many sequential layers of operations a circuit contains after considering which gates can run in parallel.
- Coherence
- The preservation of phase relationships needed for quantum interference.
- Decoherence
- Loss of quantum coherence through interaction with the environment or uncontrolled dynamics.
- Entanglement
- A property of a multi-part quantum state that cannot be represented as independent states of each subsystem.
- Error mitigation
- Techniques that reduce or estimate the effects of noise without full fault-tolerant quantum error correction.
- Fidelity
- A measure of similarity between an intended and actual quantum state, operation, or process.
- Gate
- A reversible quantum operation that transforms a quantum state.
- Grover’s algorithm
- A quantum search algorithm that provides a quadratic query-complexity improvement for unstructured search problems.
- Hadamard gate
- A single-qubit gate often used to create and recombine superpositions.
- Hybrid algorithm
- A workflow where classical and quantum processors cooperate, often in an iterative loop.
- Interference
- The combination of quantum amplitudes so outcomes can be amplified or suppressed.
- Logical qubit
- Quantum information encoded across physical qubits using error-correction techniques.
- Measurement
- The process that produces classical outcomes from a quantum system according to its state and measurement basis.
- Noise
- Unwanted effects that make real quantum operations differ from ideal mathematical operations.
- Observable
- A measurable physical quantity represented mathematically by an operator.
- Oracle
- A reversible operation that encodes or recognizes problem-specific information inside some quantum algorithms.
- Pauli X
- A single-qubit operation that swaps |0〉 and |1〉.
- Pauli Z
- A single-qubit operation that changes the relative phase of the |1〉 basis component.
- Phase
- Information in quantum amplitudes that affects interference even when immediate measurement probabilities are unchanged.
- Physical qubit
- An individual hardware implementation of a qubit.
- Post-quantum cryptography
- Classical cryptographic algorithms designed to resist known attacks from quantum computers.
- QAOA
- Quantum Approximate Optimization Algorithm, a variational approach studied for certain optimization problems.
- QFT
- Quantum Fourier Transform, a circuit transformation central to several quantum algorithms.
- Quantum advantage
- A demonstrated benefit of a quantum approach over relevant classical alternatives on a defined task and metric.
- Quantum circuit
- An ordered composition of quantum operations, measurements, and sometimes classical control.
- Quantum kernel
- A similarity function derived from quantum state encodings, often used with classical kernel methods.
- Quantum machine learning
- Methods that combine quantum computation with machine learning tasks or models.
- Quantum teleportation
- A protocol that transfers an unknown quantum state using shared entanglement plus classical communication.
- Qubit
- The basic unit of quantum information in the two-level circuit model.
- Readout error
- Error that occurs when the measurement process reports the wrong classical result.
- Shor’s algorithm
- A fault-tolerant quantum algorithm for integer factorization and related number-theoretic problems.
- Shots
- Repeated executions of a quantum circuit used to estimate an outcome distribution.
- Statevector
- A vector of complex amplitudes describing a pure quantum state in a chosen basis.
- Superposition
- A coherent linear combination of basis states.
- Surface code
- A prominent family of quantum error-correcting codes based on local stabilizer measurements.
- Tensor product
- The mathematical operation used to combine quantum state spaces.
- Transpilation
- Transforming an abstract circuit into operations and connectivity supported by a target backend.
- Unitary
- A linear transformation that preserves inner products and total probability; ideal quantum gates are unitary.
- Variational circuit
- A parameterized quantum circuit whose parameters are adjusted, usually by a classical optimizer.