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.

中文翻译：

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弱阻尼驱动的纳米力学模式的压缩效应的光谱证据

由于打破了时间平移对称性，在周期性驱动的振动系统中，不同振动分量的波动具有不同的强度。通常会压缩一种成分的波动，而另一种成分的波动会相移$\pi /2$，增加。挤压是一个多方面的现象。从高精度测量的角度来看，它引起了很多关注。在这里，我们展示了压缩的一个新的，迄今尚未得到认识的方面：它直接出现在驱动振动系统的光谱中。使用弱阻尼的纳米机械谐振器，我们研究了谐振驱动的非线性模式的热波动谱。在获得的边带分辨机制中，我们表明频谱的不对称性直接表征了压缩。这开辟了一种方法来推导在阻尼不足的谐振器中热波动的压缩，为此，频率波动阻碍了通过标准零差测量的直接确定。实验和理论结果吻合得很好。