Quantum gates (or unitary quantum operators) are the quantum computing equivalent of classical logic gates like “AND”, “OR”, “XOR”, “NOT”.
Classical logic gates are defined by their truth tables. They follow a mathematical structure called Boolean algebra. With the advancement of MOSFET transistor it became possible to implement these logic gates electrically.
Quantum gates work in a similar way. They are defined by matrices. They follow the rules of a mathematical structure called the Lie group.