  The quality of quantum bits (qubits) in silicon is highly vulnerable to
charge noise that is omni-present in semiconductor devices and is in principle
hard to be suppressed. For a realistically sized quantum dot system based on a
silicon-germanium heterostructure whose confinement is manipulated with
electrical biases imposed on top electrodes, we computationally explore the
noise-robustness of 2-qubit entangling operations with a focus on the
controlled-X (CNOT) logic that is essential for designs of gate-based universal
quantum logic circuits. With device simulations based on the physics of bulk
semiconductors augmented with electronic structure calculations, we not only
quantify the degradation in fidelity of single-step CNOT operations with
respect to the strength of charge noise, but also discuss a strategy of device
engineering that can significantly enhance noise-robustness of CNOT operations
with almost no sacrifice of speed compared to the single-step case. Details of
device designs and controls that this work presents can establish a rare but
practical guideline for potential efforts to secure silicon-based quantum
processors using an electrode-driven quantum dot platform.
