In-situ Laser Microprocessing at the Quantum Level

One of the biggest challenges of nanotechnology is the fabrication of nano-objects with perfectly controlled properties. Here we employ a focused laser beam both to characterize and to in-situ modify single semiconductor structures by heating them from cryogenic to high temperatures. The heat treatment allows us to blue-shift, in a broad range and with resolution-limited accuracy, the quantized energy levels of light and charge carriers confined in optical microcavities and self-assembled quantum dots (QDs). We demonstrate the approach by tuning an optical mode into resonance with the emission of a single QD and by bringing different QDs in mutual resonance. This processing method may open the way to a full control of nanostructures at the quantum level. In material science lasers are widely employed both for characterization and for processing/machining. In the field of semiconductors, the local heat produced by a laser source has been used, e.g., to anneal defects created by implantation [1], to locally crystallize amorphous semiconductors [1, 2, 3], to fabricate lateral transistors by local interdiffusion of doping atoms [4], to locally modify the wall structure of rolled-up nanotubes [5], to produce nanostructures by local intermixing of quantum wells (QWs) with the surrounding material [6, 7, 8], and to selectively blue-shift the emission of quantum dot (QD) arrays [9, 10]. Spatial resolutions much beyond the optical diffraction limit can be achieved [6, 11]. These examples give a flavour of the wide range of applications accessible by laser processing. In most of the studies presented so far the characterization of the fabricated/processed structures was accomplished ex-situ, with a setup independent from that used for the processing. Here we use the same focused laser beam both for characterization (at low power) and for post-fabrication processing (at high power) of single microand nano-structures, which are