Quantum gates are the quantum computing analog of classical logic gates. They are unitary linear transformations applied to qubit states. Unlike classical gates (which can be irreversible), all quantum gates are reversible because unitary matrices have inverses. Single-qubit gates include the Pauli gates (X, Y, Z), the Hadamard gate (H), and rotation gates (RX, RY, RZ). Two-qubit gates include CNOT, CZ, SWAP, and iSWAP. Three-qubit gates include Toffoli (CCX) and Fredkin (CSWAP). A universal gate set (e.g., {H, T, CNOT}) can approximate any quantum operation to arbitrary precision. In hardware, native gates vary by platform — IBM uses {CX, RZ, SX}, IonQ uses {XX, RZ}.
Related Terms
Hadamard Gate
GatesThe H gate — creates an equal superposition of |0⟩ and |1⟩ from a basis state.
CNOT Gate
GatesControlled-NOT — a two-qubit gate that flips the target qubit when the control qubit is |1⟩.
Pauli Operators
GatesThe fundamental single-qubit gates X, Y, Z — forming the basis for all quantum operations.
Toffoli Gate
GatesThe three-qubit CCX gate — flips the target qubit only when both control qubits are |1⟩.
Quantum Circuit
FundamentalsA sequence of quantum gates applied to a register of qubits, followed by measurements.