  In practical sensing tasks, noise is usually regarded as an obstruction to
better performance and will degrade the sensitivity. Fortunately,
\textit{stochastic resonance} (SR), a counterintuitive concept, can utilize
noise to greatly enhance the detected signal amplitude. Although fundamentally
important as a mechanism of weak signal amplification, and has been continually
explored in geological, biological, and physical science, both theoretically
and experimentally, SR has yet to be demonstrated in realistic sensing tasks.
Here we develop a novel SR-based nonlinear sensor using a thermal ensemble of
interacting Rydberg atoms. With the assistance of stochastic noise (either
inherently in the system or added externally) and strong nonlinearity in the
Rydberg ensembles, the signal encoded in a weak MW field is greatly enhanced
(over 25 dB). Moreover, we show that the SR-based atomic sensor can achieve a
better sensitivity in our system, which is over 6.6 dB compared to a heterodye
atomic sensor. Our results show potential advantage of SR-based MW sensors in
commercial or defense-related applications.
