Multiphotonen-Experimente mit Halbleiterquantenpunkten

Quantum physics has led us to a deeper understanding of the microscopic world and provided us with tools to quantitatively describe its mysterious phenomena. These tools have been used to create electronic devices or entire networks that have brought about radical changes in modern society - often referred to as a "quantum revolution". Based on the new ideas of quantum information processing, we are now on the verge of a "second quantum revolution": previously unused quantum phenomena could find applications in "quantum computers", with the help of which hitherto unsolvable problems could be solved, and which could also lead to the development of quantum communication systems that guarantee the highest possible security. Among the possible building blocks for this, photons - the quanta of light - are the natural choice for quantum communication and are also suitable for applications in the field of quantum computing. One of the hurdles on the way to these revolutionary applications has always been the lack of light sources capable of emitting single and multiple photons "on command". The solution to this problem could be structures of semiconductor materials in the nanometre range, which already form the basis of classical computing and communication architectures.
In the current project, we aim to establish a world-leading photonic platform based on a novel type of semiconductor photon source in combination with innovative photonic circuits, and to use it to demonstrate multiphoton quantum protocols. To achieve this goal, we combine the complementary expertise of the participating researchers at the Universities of Innsbruck, Linz and Vienna.
We focus on semiconductor quantum dots made of gallium arsenide, which show very advantageous properties, such as the ability to generate single and entangled photons with emission rates in the gigahertz range. At the same time, the colour of their light matches the range in which silicon detectors are very sensitive. However, considerable efforts will still be needed to increase the brightness of the light sources and the quality of the photons. In particular, when several such sources are used in combination, the emitted photons must be completely identical. We will address these challenges by: (i) integrating the quantum dots into microstructures that allow efficient injection of the emitted light into the photon circuits; (ii) fine-tuning the colour of the emitted photons using a patented technology; and (iii) exploring different methods of excitation for the quantum dots to increase the "purity" of the emitted photons. In parallel to improving the photon sources, we will realise increasingly complex applications and integrate them into high-performance photonic devices. Among other things, one goal is to generate "cluster states" of some photons for secure quantum computers. Suitable tests will be developed to verify the emergence of such states in experiments and to characterise the performance of the system.
The combination of the quantum light from the novel quantum dots with integrated photonic circuits on the other hand, make this research project unique. In the long run, we expect that the approach outlined here will allow us to approach the ultimate frontiers of photonic quantum information processing.