We show that the sensitivity of an atomic clock can be enhanced below the shot-noise level by initially squeezing, and then measuring in output, the population of a single atomic level. This can simplify current experimental protocols which requires squeezing of the relative number of particles of the two populated states. We finally study, as a specific application, the clock sensitivity obtained with a single mode quantum non-demolition measurement.
@article{arxiv.1004.5486,
title = {Ultrasensitive Atomic clock with single-mode number-squeezing},
author = {L. Pezze and A. Smerzi},
journal= {arXiv preprint arXiv:1004.5486},
year = {2010}
}