**Quantum complexity theory：**Quantum complexity theory Is part of the theory of computational complexity in theoretical computer science.The theory uses quantum computers and quantum information to study the definition of complexity classes. Quantum information is a calculation model based on quantum mechanics. Quantum complexity theory is used to study the difficulty of these complexity classes, and the relationship between quantum complexity classes and classic (non-quantum) complexity classes.

Complexity theory is concerned with the inherent cost required to solve in- formation processing problems, where the cost is measured in terms of various well-defined resources.