We show how simultaneous, back-action evading tracking of non-commuting observables can be achieved in a widely-used sensing technology, atomic interferometry. Using high-dynamic-range dynamically-decoupled quantum non-demolition (QND) measurements on a precessing atomic spin ensemble, we track the collective spin angle and amplitude with negligible effects from back action, giving steady-state tracking sensitivity 2.9 dB beyond the standard quantum limit and 7.0 dB beyond Poisson statistics.
@article{arxiv.1702.08888,
title = {Simultaneous tracking of spin angle and amplitude beyond classical limits},
author = {Giorgio Colangelo and Ferran Martin Ciurana and Lorena C. Bianchet and Robert J. Sewell and Morgan W. Mitchell},
journal= {arXiv preprint arXiv:1702.08888},
year = {2017}
}