Backtracking method applicable to optical quantum calculation

Optical quantum devices are promoting the development not only of communication but also of quantum computation using optical quantum gates. Here, we will explain how to replace circuits consisting of gates such as NOT, AND, and OR used in classical logic calculations with quantum calculation gates. Then, we perform reverse tracing of a quantum circuit constructed using the reversibility of quantum gates. As a simple example, we will explain how to perform factorization by backtracking a multiplier expressed as a quantum circuit.