All-optical self-referenced transverse position sensing with sub-nanometer precision

The emergence of technologies operating at the nanometer scale for applications as varied as nano-fabrication and super-resolution microscopy has driven the need for ever more accurate spatial localization. In this context, nano-structures 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 sub-wavelength nano-structure. For a particular choice of structures, gold nano-particles, we demonstrate a sub-nanometer lateral precision of 0.55 nm. The versatility of the method also allows for the use of different structures, offering a promising opportunity for sub-nanometer positioning accuracy for a wide variety of systems.