Nanoscale probing with single quantum dots

The ability to position nanoscopic objects at precise locations on a surface is essential for a broad range of applications. One such application is the positioning of quantum dots (QDs) in nanophotonic structures such as cavities or waveguides for single-photon generation, quantum dot lasers, and nonlinear optical devices. Another example is the nanoscale positioning of metallic and dielectric particles on prepared metamaterial surfaces to engineer nanoscale opto-electronic circuits. In addition, manipulation of QDs serving as biological tags could enable in situ characterization of biological molecules and controlled investigation of biological processes. The majority of these applications exploit optically resonant interactions that require the nanoscopic particles to have the correct spectral properties. These applications require particle manipulation techniques that can pre-select nanoparticles with the correct spectral properties and place them at the correct locations on a surface.

In this talk I will describe a method for manipulating particles with nanometer accuracy by controlling the flow of the surrounding liquid. This technique uses electroosmotic flow to achieve particle actuation, while imaging and feedback are used to continuously correct the particles position and move it towards the intended target. In contrast to optical tweezers whose accuracy scales inversely particle volume, the accuracy of this approach scales inversely with particle diameter making it advantageous for manipulation of nanoscopic objects. I will present our recent experimental work on the capture, quantum optical characterization, and manipulation of pre-selected single quantum dots with up to 45 nm precision using this flow control technique. I will then discuss how these approaches can be applied to probing nanoscale photonic structures. As a demonstration, we use this technique to map the local density of states of a silver nanowire. By tracking the particle along two polarizations, we are also able to directly observe interference between an emitter and its image dipole. We show that this effect can be significant for particle tracking and sensing applications, and demonstrate a method to correct for it by using polarization-resolved tracking.