Imaging and controlling electron transport inside a quantum ring

Traditionally, the understanding of quantum transport, coherent and ballistic(1), relies on the measurement of macroscopic properties such as the conductance. Although powerful when coupled to statistical theories, this approach cannot provide a detailed image of 'how electrons behave down there'. Ideally, understanding transport at the nanoscale would require tracking each electron inside the nanodevice. Significant progress towards this goal was obtained by combining scanning probe microscopy with transport measurements(2-7). Some studies even showed signatures of quantum transport in the surroundings of nanostructures(4-6). Here, scanning probe microscopy is used to probe electron propagation inside an open quantum ring exhibiting the archetype of electron-wave interference phenomena: the Aharonov - Bohm effect(8). Conductance maps recorded while scanning the biased tip of a cryogenic atomic force microscope above the quantum ring show that the propagation of electrons, both coherent and ballistic, can be investigated in situ, and can even be controlled by tuning the potential felt by electrons at the nanoscale.