or not (x v = 0). The first term of the objective function counts the number of vertices included The present QUBO formulation of the maximum clique problem differs from the previous studies, but rather is equivalent to the QUBO formulation of the maximum independent set problem proposed in Ref. 40. The formulation given in Eq. ( ) is simpler than that used in the previous studies in terms of the number of variables and terms of the objective function. According to Ref. 40, the penalty parameter A, which controls the magnitude of the penalty term, must satisfy A > 1.