Experimental Study Of Charge State Tunnel-Coupling And Decoherence In Etched Graphene Quantum Dots

Qubit is the building block of quantum information. In general, any quantum mechanical two-state system can be the candidate of qubit. However, practically, a promising candidate must balance between two contradicting requirement: accessibility and robustness against environmental fluctuation. The former one calls for a system which is well-coupled to the environment while the latter one requires the opposite. Thus, various proposals have been put forward to build quantum computer, namely, solid state system, cold atom system and optical system. Those ones each has its merits and flaws.Solid state quantum dot is one branch of solid state qubit realization which largely based on the technologies developed by semiconductor industry. In such field, scientists are always looking for new materials that best balance between the two requirements. Etched graphene quantum dot is the topic we explore in this thesis.1. In the first chapter we introduce the nanofabrication techniques we developed including new gating scheme and the application of low temperature development. These techniques improve the reproducibility and the quality of our sample2. In the third chapter we measure the interdot tunnel coupling of an etched graphene double quantum dots. The results show a sufficient tunability for further implementation, which unpredicted conventionally.3. In the first experiment in the fourth chapter, we take advantage of the hybrid device consisting of a reflection-line-resonator and a double quantum dot, and extract the decoherence time in this material. This parameter is measured for the first time.4. In the second experiment in the fourth chapter, we coupled two double quantum dots to a reflection-line-resonator. Results suggest that the electron states are distantly coupled by the microwave photon in the superconducting resonator. Furthermore, the correlation in DC transport is also studied.