Q. Quantum Computing Terminology

Working glossary (FA readers: Farsi equivalents in the FA edition). Amplitude — complex weight of a basis state; squared → probability. Ancilla — workspace qubit, must return to |0⟩. BQP — polynomial-time quantum with bounded error. Barren plateau — vanishing gradients in variational circuits. Bell state / Bell test — maximal entanglement / inequality violation certifying nonclassicality. Bloch sphere — single-qubit state geometry. Clifford / non-Clifford — Pauli-normalizing gates (cheap, classically simulable) / T and beyond (expensive, universal). Coherence (T1, T2) — relaxation / dephasing time. Coupling map — hardware connectivity graph. Decoherence — environment-induced information leakage. Density matrix — mixed-state description. Depolarizing — maximally-unbiased noise. Entanglement — inseparable joint state. Fidelity — closeness of states/operations. Logical qubit — error-corrected register. Magic state — distilled non-Clifford resource. MWPM — minimum-weight perfect matching (decoder). NISQ — pre-correction era. Oracle — black-box subcircuit. Phase kickback — eigenphase-to-register trick. QEC — quantum error correction. qLDPC — high-rate quantum low-density parity-check codes. Qubit — two-level quantum system. Shots — circuit repetitions. Stabilizer — Pauli string whose +1 eigenspace contains the code space. Statevector — full amplitude description. Superposition — weighted basis combination. Syndrome — error-location signature. Threshold — critical physical error rate enabling correction. Transpilation — circuit-to-hardware compilation. Trotterization — product-formula simulation. Unitary — norm-preserving operation. XEB — cross-entropy benchmarking. Λ (lambda) — logical-error suppression factor per distance step.