Bounds on Atomistic Disorder for Scalable Electron Shuttling

Electron shuttling, the gate-controlled, coherent transport of electrons between qubit registers, increases qubit connectivity and enables novel and efficient error-correction schemes. It is thus emerging as a key enabler of scalable silicon spin-qubit quantum computing. As an electron travels over microns, it samples angstrom-scale disorder (notably random alloying and interface roughness), causing fluctuations in its confinement potential, valley splitting, and valley phase. These lead to leakage into the valley-excited state and limit high-fidelity shuttling speeds. Reliable predictions of shuttling fidelities thus require multiscale simulations linking atomistic and mesoscopic physics.

We develop a QTCAD^®-based workflow to quantify these effects in the Si/SiGe quantum bus (QuBus) conveyor-belt architecture by combining finite-element electrostatics, atomistic tight-binding, and time-dependent Schrödinger simulations. We find that shuttling fidelities are strongly suppressed by interface roughness, with a sharp anomaly near the atomic-layer scale, thereby setting quantitative guidelines to realize scalable shuttling.