Coherent electron transport in silicon quantum dots

With silicon being the go-to material for spin qubits, and motivated by the demand of a scalable quantum computer architecture for fast and reliable quantum information transfer on-chip, we study coherent electron transport in a silicon double quantum dot. We first examine the valley-orbital dynamics in a silicon double dot, and discuss how to properly measure the tunnel couplings as well as the valley phase difference between two quantum dots. We then focus on possible phase and spin flip errors during spin transport across a silicon double dot. In particular, we clarify correction on the effective $g$-factor for the electron spin from the double dot confinement potential, and quantify the resulting phase error. We then study spin fidelity loss due to spin-valley mixing, which is a unique feature of silicon quantum dots. We show that a small phase correction between valleys can cause a significant coherence loss. We also investigate spin flip errors caused by either an external inhomogeneous magnetic field or the intrinsic spin-orbit coupling. We show that the presence of valleys makes it possible to have much broader (in terms of interdot detuning) level anti-crossings compared to typical anti-crossings in, for example, a GaAs double dot, and such broad anti-crossings lead to amplification of spin flip errors. Lastly, we design a pulse sequence to suppress various possible spin flip errors by taking advantage of the multiple level anti-crossings in a silicon double dot and employing Landau-Zener transitions.