Quantum gates are the basic operations that manipulate qubit states, much like classical logic gates (AND, OR, NOT) operate on classical bits. However, unlike classical gates, quantum gates are reversible and represented by unitary matrices, preserving quantum information.
Key Features:
- Operate on superpositions: Quantum gates can transform qubits in superposition, enabling complex quantum algorithms.
- Reversibility: All quantum gates are reversible; applying the gate’s inverse undoes its effect.
- Common single-qubit gates:
- X gate (quantum NOT): flips |0⟩ ↔ |1⟩.
- Hadamard gate (H): puts qubits into or removes them from superposition.
- Z and Y gates: rotate the qubit around different axes of the Bloch sphere.
Multi-Qubit Gates:
- CNOT (Controlled-NOT): flips the second qubit only if the first is |1⟩; key to creating entanglement.
- Toffoli gate: a universal reversible gate that can simulate classical logic.
Quantum gates are the building blocks of quantum circuits, which perform computations by manipulating qubit states through carefully designed sequences.