Unified treatment of diffraction and1fnoise

The two-particle wave function is used to study the diffraction pattern resulting from a double-slit experiment and to describe quantum $\frac{1}{f}$ noise from a beam of charged particles in vacuum. The density-matrix approach is also used to examine the case of $\frac{1}{f}$ noise resulting from a beam of scattered particles and to compare with the results we obtained with the two-particle wave-function method. The autocorrelation function was found analytically for the three cases mentioned above. The form of the autocorrelation function which we have obtained for $\frac{1}{f}$ noise is consistent with previous calculations of quantum $\frac{1}{f}$ noise, and is bilinear in the wave function, as required by the principles of quantum mechanics.