Many experiments that interrogate fundamental theories require detectors whose sensitivities are limited by the laws of quantum mechanics. In cavity-based searches for axionic dark matter, vacuum fluctuations in the two quadratures of the cavity electromagnetic field limit the sensitivity to an axion-induced field. In an apparatus designed to partially mimic existing axion detectors, we demonstrate experimentally that such quantum limits can be overcome through the use of squeezed states. By preparing a microwave cavity in a squeezed state and measuring just the squeezed quadrature, we enhance the spectral scan rate by a factor of 2.12±0.08. This enhancement is in excellent quantitative agreement with a theoretical model accounting for both imperfect squeezing and measurement.
@article{arxiv.1809.06470,
title = {Squeezed vacuum used to accelerate the search for a weak classical signal},
author = {M. Malnou and D. A. Palken and B. M. Brubaker and Leila R. Vale and Gene C. Hilton and K. W. Lehnert},
journal= {arXiv preprint arXiv:1809.06470},
year = {2020}
}