Squeezed vacuum used to accelerate the search for a weak classical signal

TL;DR

This paper demonstrates that using squeezed vacuum states in a microwave cavity can surpass quantum noise limits, significantly accelerating the search for weak classical signals like axionic dark matter.

Contribution

The study experimentally shows that squeezed states can improve spectral scan rates in cavity-based detectors, overcoming quantum noise limitations.

Findings

Spectral scan rate increased by a factor of approximately 2.12.

Experimental results agree with theoretical models including imperfections.

Squeezed states enable enhanced sensitivity in quantum-limited measurements.

Abstract

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 $2.12 \pm 0.08$. This enhancement is in excellent quantitative agreement with a theoretical model accounting for both imperfect squeezing and measurement.