Fig. 10

Circuit of the constant modular subtraction \({\texttt {ModAdd}}^{-1}(\cdot )\). Since addition is the inverse operation of subtraction and y is a known constant, we can use the reverse circuit of \({\texttt{2-Add}}_y\) to compute \(|x-y\rangle\) and denote it \({\texttt{2-Add}}_y^{-1}\). The black triangle symbols in this figure as well as all the other figures in this paper indicate that the corresponding qubit registers are modified and hold the results of the computation