Strategies for enhancing spin-shuttling fidelities in Si/SiGe quantum wells with random-alloy disorder

TL;DR

This paper investigates the challenges of spin shuttling in Si/SiGe quantum wells caused by alloy disorder and valley splitting, proposing strategies to significantly improve fidelity for scalable quantum computing.

Contribution

It identifies the impact of alloy disorder on valley splitting and demonstrates multiple mitigation strategies to enhance spin shuttling fidelity in Si/SiGe heterostructures.

Findings

Alloy disorder causes pockets of low valley splitting affecting shuttling.

Modifying heterostructure composition and electric fields can mitigate dephasing.

Combined strategies can reduce shuttling infidelity by several orders of magnitude.

Abstract

Coherent coupling between distant qubits is needed for any scalable quantum computing scheme. In quantum dot systems, one proposal for long-distance coupling is to coherently transfer electron spins across a chip in a moving potential. Here, we use simulations to study challenges for spin shuttling in Si/SiGe heterostructures caused by the valley degree of freedom. We show that for devices with valley splitting dominated by alloy disorder, one can expect to encounter pockets of low valley splitting, given a long-enough shuttling path. At such locations, inter-valley tunneling leads to dephasing of the spin wavefunction, substantially reducing the shuttling fidelity. We show how to mitigate this problem by modifying the heterostructure composition, or by varying the vertical electric field, the shuttling velocity, the shape and size of the dot, or the shuttling path. We further show that combinations of these strategies can reduce the shuttling infidelity by several orders of magnitude, putting shuttling fidelities sufficient for error correction within reach.