Spin-Valley Qubit Dynamics In Exchange Coupled Silicon Quantum Dots

TL;DR

This paper analyzes how valley states in silicon quantum dots influence spin qubit dynamics, revealing conditions under which spin-valley entanglement occurs and its impact on multiqubit gate fidelity.

Contribution

It provides a perturbative analytical framework to understand spin-valley entanglement effects in exchange-coupled silicon quantum dots, highlighting implications for quantum computing fidelity.

Findings

Spin-valley entanglement arises when valley splitting is large and electrons are not initialized to valley eigenstates.

Small valley splitting leads to spin-valley entanglement that does not affect two-qubit measurement probabilities.

Multiqubit systems are affected by valley degrees of freedom, potentially reducing gate fidelities.

Abstract

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 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 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.