A study of low-lying eigenstates in a two-electron silicon quantum dot

Electron spin qubits in silicon quantum dots are promising building blocks for universal quantum computing because of their long coherence times and high-fidelity qubit manipulation. Here we present a comprehensive study of low-lying singlet and triplet states in a two-electron Si quantum dot in the context of spin measurement in the spin blockade regime. Specifically, we examine the contributions coming from the excited orbital states in the absence of interface roughness. In the presence of interface roughness, on the other hand, we show that valley-orbit coupling could allow transitions between different valleys for ground and excited orbital states, thus lifting any possible valley blockade. We compute the energy levels and the composition of the low-lying states, and explore their dependence on dot size and interface roughness. Our results provide new insight on the controllability and detectability of silicon-based spin qubit for its use in quantum information processing.