The quantum Euclid algorithm and its application to factoring

Abstract We present a quantum implementation of the Euclid algorithm for calculating the Greatest Common Divisor when one of the integers involved is a compound of two odd-valued primes. We discuss a possible application to the quantum factoring problem, for which modular exponentiation is no longer required, and the factors are revealed directly by measurements, although the method does not scale for large numbers in a favourable manner.