The effects of alloy disorder on strongly-driven flopping mode qubits in Si/SiGe

TL;DR

This paper investigates how alloy disorder affects the performance of flopping mode spin qubits in Si/SiGe quantum dots, focusing on optimizing fidelity under charge noise and valley configuration variations.

Contribution

It provides an analysis of qubit performance considering alloy disorder and charge noise, proposing strategies to optimize fidelity across different valley configurations.

Findings

High fidelity qubits are achievable with fine-tuned pulses in weak charge noise regimes.

Large valley splittings and small valley phase differences improve fidelity in strong noise regimes.

Strong driving pulses are less sensitive to detuning but more sensitive to valley parameter shifts.

Abstract

In Si quantum dot systems, large magnetic field gradients are needed to implement spin rotations via electric dipole spin resonance (EDSR). By increasing the effective electron dipole, flopping mode qubits can provide faster gates with smaller field gradients. Moreover, operating in the strong-driving limit can reduce their sensitivity to charge noise. However, alloy disorder in Si/SiGe heterostructures randomizes the valley energy splitting and the valley phase difference between dots, enhancing the probably of valley excitations while tunneling between the dots, and opening a leakage channel. In this work, we analyze the performance of flopping mode spin qubits in the presence of charge noise and alloy disorder, and we optimize these qubits for a variety of valley configurations, in both weak and strong charge-noise regimes. When the charge noise is weak, high fidelity qubits can be implemented across a wide range of valley parameters, provided the electronic pulse is fine-tuned for a given valley configuration. When the charge noise is strong, high-fidelity pulses can still be engineered, provided the valley splittings in each dot are relatively large and the valley phase difference is relatively small. We analyze how charge noise-induced fluctuations of the inter-dot detuning, as well as small shifts in other qubit parameters, impact qubit fidelities. We find that strongly driven pulses are less sensitive to detuning fluctuations but more sensitive to small shifts in the valley parameters, which can actually dominate the qubit infidelities in some regimes. Finally, we discuss schemes to tune devices away from poor-performing configurations, enhancing the scalability of flopping-mode-based qubit architectures.