Reference

Glossary

43 terms, each with a receipt: where a term names something computable, it links to the live instrument on this site that computes it. If a definition and its instrument ever disagree, the instrument wins and the definition gets fixed.

Amplitude: The complex number attached to each basis state. Probabilities come from its squared magnitude; interference comes from its sign and phase. computed: Gate Mixer
Ansatz: A parameterized trial circuit whose knobs an optimizer turns. The VQE suite uses a single parameter ansatz that is exact for H₂. computed: VQE suite
BB84: The 1984 quantum key distribution protocol. Security comes from the fact that measuring a qubit in the wrong basis disturbs it. computed: BB84. Catch Eve
Bell state: One of four maximally entangled two qubit states. Measuring one qubit fixes the other's statistics, with no classical explanation. computed: Entangled Dice
Bloch sphere: The unit sphere picture of a single qubit: pure states are points on the surface, gates are rotations. computed: the interactive sphere
Born rule: The probability of an outcome equals the squared magnitude of its amplitude. Every collapse on this site is a real sample from it. computed: Born Casino
CHSH inequality: A Bell inequality: classical correlations obey S ≤ 2, quantum mechanics reaches 2√2. You can violate it yourself with sampled rounds. computed: CHSH
CNOT: The two qubit gate that flips a target when the control is 1. Applied to superpositions it creates entanglement. computed: Circuit Lab
Code distance: How many physical errors an error correcting code can tell apart; the scoreboard tracks it because logical error rates fall exponentially with it, below threshold. computed: hardware scoreboard
Coherence: The survival of definite phase relationships between amplitudes. Decoherence is their leak into the environment. computed: Decoherence Dial
Density matrix: The state description that also covers noise and partial knowledge. This site evolves them exactly, no Monte Carlo jitter. computed: Circuit Lab noise panel
Entanglement: Correlation between systems that no separate description of each can reproduce. Purity of a subsystem dropping below 1 is its fingerprint. computed: Entanglement Dial
Fidelity: How close two states are, as a number in [0, 1]. The steering game scores you on it. computed: State Match
Gate: A unitary operation on qubits, the reversible logic of quantum computing. Every button in the arcade multiplies a real matrix into a real statevector. computed: Gate Mixer
GHZ state: The three qubit state (|000⟩+|111⟩)/√2. It wins a referee game with certainty where classical players top out at 75%. computed: The GHZ Game
Grover search: Amplitude amplification that finds a marked item in O(√N) queries, provably optimal. Over rotate and you fly past the answer. computed: Grover Searchlight
Hadamard: The gate that turns |0⟩ into an equal superposition. Two in a row cancel, which is interference in its smallest form. computed: Interference Lab
Interference: Amplitudes adding with signs, so paths can cancel or reinforce. It is the resource every quantum algorithm actually spends. computed: Interference Lab
Kraus channel: The general mathematical form of noise acting on a density matrix. The engine's depolarizing noise is one, applied exactly. computed: engineering notes
Logical qubit: A qubit encoded across many physical qubits so errors can be detected and corrected. The scoreboard counts them; the arcade shows why they pay. computed: Repetition Rescue
Measurement: Asking a state a question in a chosen basis. The answer is random by the Born rule and the state updates. Here it is a real inverse CDF sample, never a scripted animation. computed: Measurement Duel
No cloning: No unitary process can copy an unknown quantum state. A two line linearity argument, and the reason quantum key distribution works. computed: The Cloning Button
Noise model: A device's measured error rates applied in simulation. The hardware page compares the exact prediction against ibm_brisbane's published calibration. computed: hardware
OpenQASM: The standard text format for quantum circuits. The transpiler terminal parses 2.0 and 3.0; the Circuit Lab exports 2.0. computed: transpiler terminal
Oracle: A black box subroutine an algorithm may query. Speedups are counted in queries; Bernstein and Vazirani needs exactly one. computed: Bernstein-Vazirani
Parameter shift rule: An identity giving the exact gradient of a rotation gate's expectation from two evaluations. The VQE curve is exact gradient descent because of it. computed: VQE docs
Pauli operators: X, Y, Z: bit flip, both, phase flip. They generate rotations, express Hamiltonians, and label measurement bases. computed: Bloch Detective
Phase kickback: A controlled operation writing its phase onto the control qubit. Deutsch and Grover both run on this trick. computed: Phase Kickback
Purity: Tr(ρ²), equal to 1 for pure states and 1/2 for a maximally mixed qubit. Watching it drop is watching entanglement or noise happen. computed: Entanglement Dial
QAOA: A variational circuit for combinatorial optimization. Its only proven worst case guarantee is at depth p=1 on 3-regular MaxCut. computed: QAOA MaxCut
QBER: Quantum bit error rate: the sifted key disagreement fraction in QKD. An eavesdropper pushes it toward 25%. computed: BB84. Catch Eve
Quantum Fourier transform: The unitary that turns hidden periodicity into readable peaks. It is how Shor's algorithm extracts a period. computed: QFT Period Finder
Quantum walk: The coherent counterpart of a random walk: it spreads linearly in time instead of as √t. computed: Walk Race
Qubit: A two level quantum system: a unit vector of two complex amplitudes, not a probabilistic bit. computed: Gate Mixer
Shot: One prepare and measure repetition on hardware. The hardware lane runs 1024 per job against a monthly ledger. computed: hardware
Statevector: The full list of 2ⁿ amplitudes describing n qubits. The engine holds it explicitly; the benchmark shows the 2ⁿ wall. computed: Engine Scaling Benchmark
Superdense coding: Two classical bits carried by one qubit, paid for with a pre shared entangled pair. computed: Superdense Coding
Superposition: A state with amplitude on several basis states at once. Not 'both values at the same time', a vector that measurement will project. computed: Born Casino
Teleportation: Moving a state using entanglement plus two classical bits, destroying the original. It cannot signal faster than light. computed: Teleportation Walkthrough
Threshold theorem: Below a physical error threshold, error correction can suppress logical errors arbitrarily, under stated noise assumptions. The open problems page keeps the assumptions honest. computed: open problems
Transpiler: The compiler stage that rewrites a circuit for a target: gate set, connectivity, format. This site's turns OpenQASM into Amazon Braket IR. computed: transpiler terminal
VQE: The variational quantum eigensolver: a quantum circuit proposes states, a classical optimizer tunes it toward the ground state energy. computed: VQE suite
Zero noise extrapolation: Run a circuit at amplified noise levels and extrapolate back to zero. The engine does it with Richardson extrapolation on exact density matrices. computed: ZNE demo