# Spectral Evidence of Squeezing of a Weakly Damped Driven Nanomechanical Mode

## TL;DR

This paper demonstrates that spectral asymmetry in a driven nanomechanical resonator directly indicates squeezing of thermal fluctuations, providing a new method to detect quantum and thermal squeezing in underdamped systems.

## Contribution

It reveals the spectral signature of squeezing in driven nanomechanical modes, enabling detection without homodyne measurement, and extends the theory to quantum fluctuation squeezing.

## Key findings

- Spectral asymmetry characterizes squeezing in the studied resonator.
- Experimental and theoretical results show excellent agreement.
- Method allows squeezing detection in strongly underdamped resonators.

## Abstract

Because of the broken time-translation symmetry, in periodically driven vibrational systems fluctuations of different vibration components have different intensities. Fluctuations of one of the components are often squeezed, whereas fluctuations of the other component, which is shifted in phase by {\pi}/2, are increased. Squeezing is a multifaceted phenomenon; it attracts much attention from the perspective of high-precision measurements. Here we demonstrate a new and hitherto unappreciated side of squeezing: its direct manifestation in the spectra of driven vibrational systems. With a weakly damped nanomechanical resonator, we study the spectrum of thermal fluctuations of a resonantly driven nonlinear mode. In the attained sideband-resolved regime, we show that the asymmetry of the spectrum directly characterizes the squeezing. This opens a way to deduce squeezing of thermal fluctuations in strongly underdamped resonators, for which a direct determination by a standard homodyne measurement is impeded by frequency fluctuations. The experimental and theoretical results are in excellent agreement. We further extend the theory to also describe the spectral manifestation of squeezing of quantum fluctuations.