Physics Colloquium: “Spin Qubits in Si: Coherence and Control”

Xuedong Hu

University at Buffalo, Department of Physics

Abstract: Electron spin qubits in Si are promising candidates as building blocks toward future scalable quantum computers. Tremendous progress has been made in the past decade in demonstrating the exceptional coherence properties of spins confined in quantum dots and donors.  However, studies of high-fidelity manipulation of spin qubits have encountered numerous problems as well: for donors, the small Bohr radius makes donor electrons hard to locate and control; for quantum dots, especially ones in Si/SiGe heterostructures, small valley splitting makes spin detection based on spin blockade difficult to realize. In this talk I discuss our recent work on spin manipulation and decoherence in Si quantum dots.  I will first show that the complex valley-orbit coupling in a Si quantum dot can be significantly impacted by the atomistic scale features of an interface.  The different valley mixing angles across a double dot would remove all valley selection rules in electron tunneling, and cause significant modification to the two-electron exchange coupling.   On the decoherence front, I will discuss our recent study of spin relaxation in a Si quantum dot under the influence of a micromagnet that allows electrical control of single spins in Si.  We show that the field gradient generated by a micromagnet amounts to an artificial spin-orbit interaction.  However, unlike intrinsic spin-orbit coupling, which causes only spin relaxation, a micromagnet would cause both spin relaxation and pure dephasing, and generate a longitudinal effective field that could potentially be used for spin manipulation.

We thank support by US ARO.

All lectures are via Zoom: https://mines.zoom.us/j/98686472990?pwd=REFBbFBJZk9MbXhldGRzemNaczlTZz09

Short Bio: Xuedong Hu is a physics professor at the University at Buffalo, the State University of New York.  He received his PhD degree in condensed matter theory from University of Michigan in 1996, supervised by Franco Nori.  He was introduced to the field of solid state quantum information processing in 1998 as a postdoc in Sankar Das Sarma’s group at the University of Maryland. His recent research focus is on spin qubits in silicon.