Gravitational-wave detectors, such as the Laser Interferometer Gravitational-Wave Observatory (LIGO), are sensitive to very small changes in the displacement of spacetime. In a recent work, Wenxuan Jia and colleagues have shown that a reduction in the noise level of a LIGO detector three decibels below the standard quantum limit (SQL) can be achieved for a certain frequency range by using frequency-independent squeezed vacuum states and a filter cavity.

The authors used the combination of quantum squeezed states with a detuned and overcoupled Fabry–Pérot cavity, which converts the frequency-independent states from a squeezer to the frequency-dependent states, such that the noise can be reduced for a broader frequency range. These squeezed states (or non-classical light states) represent quantum states of light with correlation between photon pairs. In these states it is possible to reduce one form of noise (imprecision noise) at the expense of the other (quantum back action noise) to a limit allowed by the Heisenberg uncertainty principle. The two noise types are conjugate variables such that uncertainty in one noise increases while the other noise is measured precisely. The filter cavity used by the authors rotates the squeezed states depending on their frequency and reduces the noise. They have subtracted the measurements with unsqueezed states from the squeezed ones in their analysis and the results clearly show that the squeezed quantum noise surpasses the SQL between 35 and 75 Hz by a maximum of 3 dB.

引力波探测器，如激光干涉仪引力波天文台 （LIGO），对时空位移的非常小的变化很敏感。在最近的一项工作中，Wenxuan Jia 及其同事表明，通过使用与频率无关的压缩真空态和滤光片腔，可以在一定频率范围内将 LIGO 探测器的噪声水平降低到低于标准量子极限 （SQL） 三分贝的位置。

作者将量子压缩态与失谐和过耦合的法布里-佩罗腔相结合，将频率无关态从压缩器转换为频率相关态，从而可以在更宽的频率范围内降低噪声。这些压缩态（或非经典光态）表示光的量子态，光子对之间具有相关性。在这些状态下，可以以牺牲另一种形式的噪声（量子反作用噪声）为代价将一种形式的噪声（不精确噪声）降低到海森堡不确定性原理允许的极限。这两种噪声类型是共轭变量，因此一种噪声的不确定性增加，而另一种噪声的测量精度更高。作者使用的滤波器腔根据其频率旋转压缩态并降低噪声。他们在分析中从压缩状态中减去了未压缩状态的测量值，结果清楚地表明，压缩的量子噪声在 35 到 75 Hz 之间比 SQL 高出 3 dB。