The problem of factorising positive integer N into two integer factors x and y is first reformulated as an optimisation problem over the positive integer domain of either of the Diophantine polynomials Q x y N N xy x x y ,, of each of which the optimal solution is unique with x N y , and x=1 if and only if N is prime. An algorithm in the context of Adiabatic Quantum Computation is then proposed for the general factorisation problem.Factoring an integer into its prime constituents has attracted much interest since the advance of the RSA publicprivate key encryption [1]. It is suspected that factorisation is NP-intermediate, that is, in the NP class but may be not quite NP-complete. While there does not yet exist any polynomial-time algorithm for the problem on a classical/Turing computer, the discovery of Shor's quantum algorithm with quantum circuits [2] has been one of the main motivations for research into quantum computation and building of quantum computers.In this paper we also consider the factorisation problem in the realm of quantum computation but with adiabatic processes, in complementary addition to the computation with quantum circuits. Also recently, the authors of [3] have considered the problem with quantum annealing. We first reformulate in the next section the factorisation into two integer factors as an optimisation of some corresponding Diophantine polynomials over the integer domain. The optimisation could also be repeatedly applied to any integer having more than two prime factors. Based on this reformulation, we then present an algorithm in the context of AQC (Adiabatic Quantum Computation) for the general factorisation problem. Following that are some numerical illustrations of the algorithm and discussion on the lower bound of the computing time with the help of an energy-time uncertainty relation. The paper is then concluded with some remarks.
Factorisation as an optimisation problemWe first consider the problem of factorising a natural integer N into two integer factors x and y. We propose that this problem can be reformulated as an optimisation problem over the integer domain of the following Diophantine polynomial