Project outline

The purpose of the project is to enhance the research activities of the three participating groups, aimed at the complete theoretical description and experimental characterization of the physical processes that underlie the simultaneous coherent interaction of optical and mechanical (strain) fields with quantum emitters in solids. In this project conceptual theoretical work will be complemented by the experimental implementation of the proposed schemes.

On the general level, the proposed work is motivated by the rapid development of quantum technolo-gies, which revealed the problem of combining all the required functionalities of a quantum computing and communication system (e.g. a quantum network) on a single technological platform. For instance, super-conducting systems, operating on sub-meV transitions, have seen tremendous progress as quantum processors, while the only viable channel for large-scale, long-haul quantum communication are optical fiber systems interfaced with quantum emitters (QEs) like semiconductor quan-tum dots (QDs) or NV defect centers in diamond.

At this point, the idea of a hybrid quantum system emerges, which combines complementary strengths of dissimilar physical systems, while at the same time avoiding their individual shortcomings. Implementing this idea requires developing different concepts for transmission, manipulation and storage, as well as developing transduction schemes for quantum information transfer between systems of different physical nature. Mechanical vibrations of a crystal, in particular acoustic waves, are considered an important resource for these applications, offering efficient coupling to all solid state systems and nanoscale integration possibilities due to their many orders of magnitude lower wavelengths as compared to light of the same frequency.

This general concept is challenged by a range of theoretical and experimental problems that we propose to address in this project. One needs to develop a full theoretical framework including quantum mechanical treatment of the interaction between phonons, electronic excitations and light, including the environmental impact on the quantum dynamics. In the experiment, we plan to study the optical properties of mechanically modulated systems as well as the interaction with confined phonon modes in the low-temperature quantum regime of cavity quantum acoustooptics, thus immediately implementing part of the theoretical findings and providing immediate feedback for further modeling. The three collaborating groups have already started to jointly develop experimental and theoretical capabilities to study hybrid quantum acousto-optical systems based on an optically active QD interacting with surface acoustic waves (SAWs) (Weiß 2021, Wigger 2021). The current challenge is to go down to the quantum limit of confined phonon modes and to demonstrate reciprocal quantum information transfer between acoustic waves and optical signals.