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Spin-Valley Qubit Dynamics in Exchange-Coupled Silicon Quantum Dots

TitleSpin-Valley Qubit Dynamics in Exchange-Coupled Silicon Quantum Dots
Publication TypeJournal Article
Year of Publication2021
AuthorsD. Buterakos, and S. Das Sarma
JournalPRX Quantum
Date PublishedDEC 23
Type of ArticleArticle

The presence of valley states is a significant obstacle to realizing quantum information technologies in silicon quantum dots, as leakage into alternate valley states can introduce errors into the computation. We use a perturbative analytical approach to study the dynamics of exchange-coupled quantum dots with valley degrees of freedom. We show that if the valley splitting is large and electrons are not properly initialized to valley eigenstates, then the time evolution of the system will lead to spin-valley entanglement. Spin-valley entanglement will also occur if the valley splitting is small and electrons are not initialized to the same valley state. Additionally, we show that for small valley splitting, spin-valley entanglement does not affect the measurement probabilities of two-qubit systems; however, systems with more qubits will be affected. This means that two-qubit gate fidelities measured in two-qubit systems may miss the effects of valley degrees of freedom. Our work shows how the existence of valleys may adversely affect multiqubit fidelities even when the system temperature is very low. Although this is not an immediate problem in Si qubits, because the current focus is on controlling individual qubits, our work points to a possible future issue in many-qubit Si circuits.