Analyzing the sensitivity of an atom interferometer with a phase-modulation readout scheme

The sensitivity of an interferometer depends on its readout scheme. However, little attention has been paid to the readout schemes of atom interferometers from the viewpoint of their sensitivity. The difference in sensitivity between readout schemes or their optimization has not been considered in the literature. Herein we analytically calculate the sensitivities of an atom interferometer with typical readout schemes by applying the two-photon formalism, which was developed for optical interferometers to deal with quantum noise. Our calculations reveal that by using sinusoidal phase modulation, the sensitivity can surpass that obtained by the conventional phase sweeping scheme. The superiority of this phase modulation scheme for both cold and thermal atomic beams is demonstrated. In addition, we show that the phase modulation scheme is advantageous for atom-flux fluctuation and resists atom-flux drift. This study performs a general analysis of the sensitivity of atom interferometers and identifies an advantageous readout scheme.