Among the known resources of quantum metrology, one of the most practical and efficient is squeezing. Squeezed states of atoms and light improve the sensing of the phase, magnetic field, polarization, mechanical displacement. They promise to considerably increase signal-to-noise ratio in imaging and spectroscopy, and are already used in real-life gravitational-wave detectors. But despite being more robust than other states, they are still very fragile, which narrows the scope of their application. In particular, squeezed states are useless in measurements where the detection is inefficient or the noise is high. Here, we experimentally demonstrate a remedy against loss and noise: strong noiseless amplification before detection. This way, we achieve loss-tolerant operation of an interferometer fed with squeezed and coherent light. With only 50% detection efficiency and with noise exceeding the level of squeezed light more than 50 times, we overcome the shot-noise limit by 6 dB. Sub-shot-noise phase sensitivity survives up to 87% loss. Application of this technique to other types of optical sensing and imaging promises a full use of quantum resources in these fields.

在已知的量子计量资源中，最实用，最有效的方法之一就是进行压缩。原子和光的压缩状态改善了对相位，磁场，极化，机械位移的感应。它们有望显着提高成像和光谱学中的信噪比，并且已经在现实生活中的重力波探测器中使用。但是，尽管它们比其他国家更强大，但它们仍然非常脆弱，从而缩小了其适用范围。特别地，在检测效率低或噪声高的测量中，压缩状态是无用的。在这里，我们通过实验证明了一种针对损耗和噪声的补救措施：在检测之前进行强大的无噪声放大。这样，我们实现了干涉仪的压缩和相干光的容错操作。凭借仅50％的检测效率，并且噪声超过了被压缩的光的水平超过50倍，我们克服了6 dB的散粒噪声限制。亚散粒噪声相位灵敏度可承受高达87％的损失。将该技术应用于其他类型的光学传感和成像技术有望在这些领域中充分利用量子资源。