Glossary

A technique that increases the probability of desired outcomes by iterating oracle + reflection-like operations.

A chosen parameterized circuit structure used to represent a family of quantum states.

The execution target for a quantum circuit, such as a simulator or a real hardware device.

A maximally entangled two-qubit state that exhibits strong measurement correlations.

A geometric representation of pure single-qubit states as points on the surface of a unit sphere.

The rule that measurement probabilities are given by squared amplitude magnitudes in the measurement basis.

A quantum circuit is a sequence of gates arranged over time, acting on qubits and usually ending with measurement.

Translating an abstract circuit into operations that a specific backend can execute.

Which pairs of qubits can interact directly with a native two-qubit operation.

The process by which a quantum system loses coherent phase relationships due to interactions with its environment.

The “inversion about the mean” operation used in Grover’s algorithm to amplify the marked state’s amplitude.

A correlation structure where a joint quantum state cannot be factored into states of its subsystems.

A rate (or probability) describing how often an operation or measurement deviates from the ideal behavior.

The average value of a measurement outcome (or observable) over many repeated trials.

A quantum gate is a (typically unitary) operation applied to one or more qubits, represented by a matrix.

A measure of how close a real gate implementation is to the ideal gate operation.

An operator that represents energy in quantum mechanics and is often the objective in algorithms like VQE.

A summary of how often each measurement outcome occurred across many shots.

A superconducting circuit element that enables nonlinear quantum behavior used to form superconducting qubits.

An error-protected qubit encoded into multiple physical qubits so it behaves more like an ideal qubit.

An operation that produces a classical outcome with probabilities determined by the quantum state and the measurement basis.

A Hermitian operator whose eigenvalues correspond to possible measurement outcomes.

A subroutine (often a reversible circuit) that marks or identifies solutions in an algorithm such as Grover’s.

A set of basic single-qubit matrices (I, X, Y, Z) used to describe qubit operations and observables.

A real hardware element that stores quantum information, such as a superconducting circuit or trapped ion.

A set of methods that attempt to reconstruct how an operation transforms quantum states by measuring many input-output configurations.

A computation model that encodes problems as an energy landscape and slowly evolves the system toward low-energy solutions.

The basic unit of quantum information, described by a normalized state in a 2D complex vector space.

A protocol that estimates average gate performance by running random sequences and analyzing how performance decays with depth.

Error in the measurement process that causes the reported classical bit to differ from the qubit’s actual measured outcome.

One repeated execution of the same quantum circuit, producing one measurement outcome (bitstring).

A classical program that predicts a circuit’s behavior under an ideal model (or an explicit noise model).

A vector of complex amplitudes describing a pure quantum state in a chosen basis.

A quantum state can be a linear combination of basis states, with complex amplitudes.

A two-qubit gate that exchanges the states of two qubits.

A relaxation timescale describing how quickly a qubit returns toward its ground state.

A dephasing timescale describing how quickly relative phases in a qubit state become scrambled.

The operation $\otimes$ that combines state spaces of subsystems into a joint state space.

The graph structure formed by qubits (nodes) and their available interactions (edges).

A linear operator $U$ that preserves inner products; equivalently $U^\dagger U = I$.

A hybrid algorithm that uses a parameterized quantum circuit and a classical optimizer to minimize an energy-like objective.

An error-mitigation method that estimates a zero-noise result by running circuits at multiple noise levels and extrapolating.