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Glossary

Quantum glossary

NISQ

Also: noisy intermediate-scale quantum

John Preskill’s name for today’s era: devices with tens to a few thousand noisy qubits and no full error correction.

NISQ algorithms — VQE, QAOA and variational classifiers — use short circuits and lean on classical optimisation to cope with noise. Whether they deliver a practical advantage before fault tolerance arrives is an open question.

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Related terms

  • Variational quantum eigensolver — A hybrid algorithm that estimates a Hamiltonian’s ground-state energy by optimising a variational circuit.
  • QAOA — A variational algorithm for combinatorial optimisation that alternates a problem Hamiltonian with a mixing Hamiltonian.
  • Error mitigation — Techniques that reduce the bias noise introduces into results, without the qubit overhead of full error correction.