All-Optical Self-Referenced Transverse Position Sensing with Subnanometer Precision

The emergence of technologies operating at the nanometer scale for applications as varied as nanofabrication and super-resolution microscopy has driven the need for ever more accurate spatial localization. In this context, nanostructures have been used as probes in order to provide a reference to track lateral drifts in the system. Yet nanometer precision remains challenging and usually involves complicated measurement apparatus. In this work we report a simple method based on symmetry considerations to measure the position of a subwavelength nanostructure. For a particular choice of structures, gold nanoparticles, we demonstrate a subnanometer lateral precision of 0.55 nm. The versatility of the method also allows for the use of different structures, offering a promising opportunity for subnanometer positioning accuracy for a wide variety of systems.