Input States for Enhancement of Fermion Interferometer Sensitivity

A conventional fermion interferometer, in which the fermions enter only one of the two input ports, can achieve a phase sensitivity $\Delta \phi =\frac{1}{\sqrt{n}}$, where $n$ is the total number of fermions which have passed through the interferometer. Here it is shown that by injection of fermions into both input ports the phase sensitivity can approach $\frac{1}{n}$ provided that the fermions in the two input beams are suitably correlated.