Emergent Transport Phenomena in Low-dimensional superconductor and semiconductor towards quantum computing


     The exploration of new states of matter for quantum computation has been at the forefront of condensed matter physics research. The realization of quantum computing is theoretically proposed in various systems, and significant experimental progress has been made on superconductor, semiconductor and Majorana fermion based devices. For superconducting quantum bit (qubit), it is key to understand the emergent, particularly, transport quantum phenomenon resulting from restricted dimensionality and electronic interactions. In this talk, transport measurements on low dimensional superconductors were carried out in a customized dilution refrigerator which hosts an assortment of in situ capabilities. It enabled a systematic study of the superconductor-insulator transitions in low dimensional superconducting systems, and led to the discovery of giant enhancement of superconductivity by a parallel magnetic field in ultrathin Pb films. For semiconductor spin qubit, the study of spin coherence and relaxation is of crucial importance. Here, I will present measurements of spin relaxation rate in a gate defined single-electron GaAs quantum dot. The spin relaxation rate W exhibits strong anisotropy: a sinusoidal dependence on the B-field angle f with a period of 180o. The periodicity is attributed to the interplay of Rashba and Dresselhaus spin orbit interactions. The results have tremendous impact on optimizing spin qubit operation.