Speaker – Ross Leon, UNSW Sydney:
Once the periodic properties of atoms were unveiled, chemical bonds could be understood in terms of the valence of atoms. Ideally, this rationale would extend to quantum dots,and quantum computation would be performed by merely controlling electrons in the outer shell. Imperfections in the semiconductor material, even at the atomic scale, disrupt this analogy between atoms and quantum dots, so that real devices seldom display such intelligible many-electron arrangement. We demonstrate here an electrostatic quantum dot that overcomes the hardships of disorder and reveals a well defined shell structure. We observe four shells (31 electrons) with multiplicities given by spin and valley degrees of freedom. We explore various fillings consisting of a single valence electron — namely 1, 5, 13 and 25 electrons — as potential qubits. An integrated micromagnet allows us to perform electrically driven spin resonance (EDSR). Higher shell states are shown to be more susceptible to the driving field, leading to faster Rabi rotations of the qubit. We investigate the impact of orbital excitations of the p and d-shell electrons on single qubits as a function of the dot deformation. This allows us to tune the dot excitation spectrum and exploit it for faster qubit control. Furthermore, hotspots arising from this tunable energy level structure provide a pathway towards fast spin initialisation.