Optical monitoring of the position and alignment of objects with a precision of only a few nanometres is key in applications such as smart manufacturing and force sensing. Traditional optical nanometrology requires precise nanostructure fabrication, multibeam interference or complex postprocessing algorithms, sometimes hampering wider adoption of this technology. Here we show a simplified, yet robust, approach to achieve nanometric metrology down to 2 nm resolution that eliminates the need for any reference signal for interferometric measurements. We insert an erbium-doped quartz crystal absorber into a single Fabry–Pérot cavity with a length of 3 cm and then induce exceptional points by matching the optical loss with the intercavity coupling. We experimentally achieve a displacement response enhancement of 86 times compared with lossless methods, and theoretically argue that an enhancement of over 450 times, corresponding to subnanometre resolution, may be achievable. We also show a fivefold enhancement in the signal-to-noise ratio, thus demonstrating that non-Hermitian sensors can lead to improved performances over the Hermitian counterpart.

以仅几纳米的精度对物体的位置和对准进行光学监测是智能制造和力传感等应用的关键。传统的光学纳米计量学需要精确的纳米结构制造、多光束干涉或复杂的后处理算法，有时会阻碍这项技术的广泛采用。在这里，我们展示了一种简化但稳健的方法，可实现低至 2 nm 的纳米计量，无需任何参考信号即可进行干涉测量。我们将掺铒石英晶体吸收器插入长度为 3 cm 的单个 Fabry-Pérot 腔中，然后通过将光损耗与腔间耦合匹配来诱导特殊点。与无损方法相比，我们实验实现了 86 倍的位移响应增强，并从理论上认为可以实现超过 450 倍的增强，对应于亚纳米分辨率。我们还展示了信噪比的五倍增强，从而证明非厄米特传感器可以比埃尔米特传感器提高性能。