Quantum mechanics places noise limits and sensitivity restrictions on physical measurements. The balance between unwanted backaction and the precision of optical measurements imposes a standard quantum limit (SQL) on interferometric systems. In order to realize a sensitivity below the SQL, it is necessary to leverage a backaction evading measurement technique, reduce thermal noise to below the level of backaction, and exploit cancellations of any excess noise contributions at the detector. Many proof of principle experiments have been performed, but only recently has an experiment achieved sensitivity below the SQL. In this work, we extend that initial demonstration and realize sub-SQL sensitivity nearly two times better than previous measurements, and with an architecture applicable to interferometric gravitational wave detectors. In fact, this technique is directly applicable to Advanced LIGO, which could observe similar effects with a detuned signal recycling cavity. We measure a total sensitivity below the SQL by 2.8 dB, corresponding to a reduction in the noise power by $72\pm 5.1\%$ below the quantum limit. Through the use of a detuned cavity and the optical spring effect, this noise reduction is tunable, allowing us to choose the desired range of frequencies that fall below the SQL. This result demonstrates access to sensitivities well below the SQL at frequencies applicable to LIGO, with the potential to extend the reach of gravitational wave detectors further into the Universe.

中文翻译：

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使用光学弹簧超越标准量子极限


量子力学对物理测量设置了噪声限制和灵敏度限制。不需要的反作用和光学测量精度之间的平衡对干涉测量系统施加了标准量子限制 (SQL)。为了实现低于 SQL 的灵敏度，有必要利用反作用规避测量技术，将热噪声降低到反作用水平以下，并利用消除检测器上任何过量噪声贡献的方法。已经进行了许多原理证明实验，但直到最近才有一项实验达到了低于 SQL 的灵敏度。在这项工作中，我们扩展了最初的演示，并实现了比以前测量高出近两倍的 sub-SQL 灵敏度，并且具有适用于干涉引力波探测器的架构。事实上，这项技术直接适用于高级 LIGO，它可以通过失谐信号回收腔观察到类似的效应。我们测得总灵敏度低于 SQL 2.8 dB，对应于噪声功率降低 $72\pm 5.1\%$ 低于量子极限。通过使用失谐腔和光学弹簧效应，这种降噪是可调的，使我们能够选择低于 SQL 的所需频率范围。这一结果表明，在适用于 LIGO 的频率下可以获得远低于 SQL 的灵敏度，有可能将引力波探测器的覆盖范围进一步扩展到宇宙。