Thermometry and laser cooling in erbium-doped nanophotonic silicon waveguides

• Applicants: Professor Dr. Andreas Reiserer; Dr. Kilian Sandholzer
• Subject Area: Experimental Condensed Matter Physics
• Term: since 2025
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 559594594

Understanding and exploring quantum effects in silicon nanostructures provide the basis for exploiting this platform for quantum technologies such as sensing, computing, or spin-photon interfaces. A crucial part of this effort is the thermal management of such nanostructures, currently done with cryocoolers. An intriguing alternative would be optical refrigeration, providing a local, non-contact, and vibration-free cooling method. In nanostructures, this may be aided by reducing bulky overheads and a simultaneous simplified isolation from the environment. However, optical cooling of silicon and other semiconductors is an open challenge, and cooling to cryogenic temperature has only been achieved using rare-earth ions doped to macroscopic large band gap host crystals. In this proposal, we aim to overcome this challenge by combining the precise engineering of light modes in nanophotonic devices with erbium dopants in silicon nanostructures to achieve direct optical cooling. The first step is to use optical precision spectroscopy of the erbium dopants to develop a local thermometer. Thermal isolation is achieved by attaching the nanostructures to tapered optical fibers, which at the same time ensures efficient optical coupling. With this, the thermalization dynamics via radiative and conductive processes will be determined for waveguides with sub-wavelength dimensions, and the material absorption will be quantified. Finally, the feasibility of optical cooling will be explored. If successful, our approach will open new possibilities for vibration-free cooling of silicon nanostructures, with possible applications in quantum optomechanical devices, low-noise photodetectors, and silicon-based sensors with improved sensitivity.

• DFG Programme: Research Grants