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International Journal of Theoretical Physics

Design and Modelling of Silicon Quantum Dot Based Single Qubit Spin Quantum Gates

Hilal Ahmad Bhat, Gul Faroz A. Malik, Farooq Ahmad Khanday

Published Nov 4, 2022• 4 citations
Publisher
DOI
10.1007/s10773-022-05239-y

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With recent experimental advancements demonstrating high-fidelity universal logic gates and basic programmability, silicon-based spin quantum bits (qubits) have emerged as promising candidates for scalable quantum computing. However, implementation of more complex quantum information protocols with many qubits still remains a critical challenge for realization of practical programmability in silicon devices. In this study, we present a computational investigation of entanglement-based quantum information applications implemented on an electrically defined quantum dot structure in silicon. Using in-house multi-scale simulations based on tight-binding calculations augmented with classical physics with bulk properties, we model a five quantum dot system that can create up to five electron spin qubits, and discuss details of control engineering needed to implement single-qubit rotations and two-qubit logic operations in a programmable manner. Using these elementary operations, we design a five-qubit quantum teleportation protocol and computationally verify its end-to-end operation including a simple but clear analysis on how the designed circuit can be affected by charge noise. With engineering details that are not well uncovered by experiments, our results demonstrate the advanced programmability of silicon quantum dot systems, delivering the practical guidelines for potential designs of quantum information processes based on electrically defined silicon quantum dot structures.
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Spin qubits in silicon quantum dots are one of the most promising building blocks for large scale quantum computers thanks to their high qubit density and compatibility with the existing semiconductor technologies. High fidelity single-qubit gates exceeding the threshold of error correction codes like the surface code have been demonstrated, while two-qubit gates have reached 98% fidelity and are improving rapidly. However, there are other types of error --- such as charge leakage and propagation --- that may occur in quantum dot arrays and which cannot be corrected by quantum error correction codes, making them potentially damaging even when their probability is small. We propose a surface code architecture for silicon quantum dot spin qubits that is robust against leakage errors by incorporating multi-electron mediator dots. Charge leakage in the qubit dots is transferred to the mediator dots via charge relaxation processes and then removed using charge reservoirs attached to the mediators. A stabiliser-check cycle, optimised for our hardware, then removes the correlations between the residual physical errors. Through simulations we obtain the surface code threshold for the charge leakage errors and show that in our architecture the damage due to charge leakage errors is reduced to a similar level to that of the usual depolarising gate noise. Spin leakage errors in our architecture are constrained to only ancilla qubits and can be removed during quantum error correction via reinitialisations of ancillae, which ensure the robustness of our architecture against spin leakage as well. Our use of an elongated mediator dots creates spaces throughout the quantum dot array for charge reservoirs, measuring devices and control gates, providing the scalability in the design.