Master thesis defense by Laurits Piehorsch

Color centers in silicon nanostructures at mK cryogenics

Photonic quantum computing with solid state spin registers presents a promising path to utility scale quantum computing. Compared to more mature quantum computing platforms, the investigation of optical spin-photon interfaces in the telecommunications band only started in the last decade. Color centers in silicon can be such interfaces. The T-center in particular emerged as a promising candidate due to its photon emis[1]sion in the original telecommunication band and long spin coherence times. Initial characterizations were done at cryogenic temperatures as low as 1.2 K, including pho[1]toluminescence spectra at magnetic fields and coherence times. Even the entanglement of two separated T-centers has been demonstrated. To estimate resource requirements for a utility scale quantum computer based on color centers, it is crucial to compare the relevant noise processes in various temperature regimes. This work covers the establishment of a dilution refrigerator with optical access, and measurements that probe and control solid state emitters at temperatures < 50 mK. First measurements on ensembles of T-centers demonstrate the successful set-up by probing the instantaneous homogeneous linewidth and an orientation-averaged hole gyromagnetic factor. Additionally, a series of measurements at temperatures from 100 mK to 10 K reveals a phonon-mediated process, governing the effective decay rate. To motivate the pursuit of this platform as well as hardware choices, the thesis includes a brief review of current plans for how such a quantum computer could be constructed.