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Glossary

Quantum glossary

CNOT gate

Also: controlled not, cx, controlled x

A two-qubit gate that flips the target qubit if and only if the control qubit is |1⟩.

Applied to a control in superposition it produces entanglement, which makes it the workhorse two-qubit gate. On hardware it is typically an order of magnitude noisier than a single-qubit gate, so the number of CNOTs is the cost metric that matters.

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Related terms

  • Bell state — One of four maximally entangled two-qubit states; the simplest and most-used form of entanglement.
  • Entanglement — A correlation between quantum systems so strong that the whole has a definite state while the parts do not.
  • Universal gate set — A small set of gates from which any quantum computation can be approximated to arbitrary accuracy.