Quantum Optical Control of Donor-bound Electron Spins in GaAs

Abstract

This thesis presents experimental research on coherent manipulation by laser light of the quantum state of an ensemble of electron spins in a solid. The medium is formed by donor-bound electron spins in GaAs. The coherent manipulation is achieved with a technique that was till now mostly explored with atomic vapors. Applying this to a donor-bound electron ensemble is possible at low temperature and low donor concentration, where neighboring electrons do not interact. Under these conditions, the electron ensembles and atomic vapors have similar properties. However, the solid-state medium has the advantage of easy integration with existing semiconductor technologies, and is thereby a more suitable system for quantum information technologies. Moreover, the rich interactions between the spins and their environment in GaAs make it an interesting system for exploring new physics. In order to control the electron spins with lasers at low temperature we built a dedicated experimental setup, which allows mechanical positioning of the sample in a helium cryostat with sub-micrometer precision. The laser light is delivered to the sample by an optical fiber. In a high magnetic field, we observed and controlled quantum phenomena that result in optical transparency for transitions that are addressed with a resonant laser. This gives access to a robust technique for controlling strong interactions between quantum optical signal fields and quantum states of spins. Our results thereby provide all the experimental techniques that are needed for future experiments on demonstrating the preparation of nonlocal quantum entanglement between spin excitations in two different ensembles.