Factoring and Fourier transformation with a Mach-Zehnder interferometer

The scheme of Clauser and Dowling [Phys. Rev. A 53, 4587 (1996)] for factoring $N$ by means of an $N$-slit interference experiment is translated into an experiment with a single Mach-Zehnder interferometer. With dispersive phase shifters, the ratio of the coherence length to wavelength limits the numbers that can be factored. A conservative estimate permits $N\approx {10}^7$. It is furthermore shown that sine and cosine Fourier coefficients of a real periodic function can be obtained with such an interferometer.