Quantum gate
양자 게이트
The basic operation that changes the state of a qubit. A quantum computer calculates by chaining these operations in order.
Overview
An ordinary computer calculates by chaining together a huge number of simple rules, such as "if both are 1, output 1." A quantum computer is similar. It calculates by linking basic operations, such as putting a qubit into superposition or entangling two qubits. Each of these operations is a quantum gate, and a list of gates in order is called a quantum circuit.
In the superconducting approach, gates are applied with radio signals. In the trapped ion approach, they are applied with lasers. The problem is that every gate comes out slightly wrong. How accurately a gate is applied is called its fidelity. In a calculation that needs thousands of gates in a row, even small errors pile up and ruin the answer.
An everyday example
In cooking terms, qubits are the ingredients, gates are each step of preparation like "chop" or "stir-fry," and a quantum circuit is the whole recipe written out in order.
Why it matters
Quantum news often mentions "gate fidelity" along with the number of qubits. Even with many qubits, if the gates are often wrong, the computer cannot finish a useful calculation.
Also calledquantum logic gate