An error-corrected quantum processor will require millions of qubits, accentuating the advantage of nanoscale devices with small footprints, such as silicon quantum dots. However, as for every device with nanoscale dimensions, disorder at the atomic level is detrimental to qubit uniformity. Here we investigate two spin qubits confined in a silicon double-quantum-dot artificial molecule. Each quantum dot has a robust shell structure and, when operated at an occupancy of 5 or 13 electrons, has single spin-21 valence electron in its p- or d-orbital, respectively. These higher electron occupancies screen atomic-level disorder. The larger multielectron wavefunctions also enable significant overlap between neighbouring qubit electrons, while making space for an interstitial exchange-gate electrode. We implement a universal gate set using the magnetic field gradient of a micromagnet for electrically-driven single qubit gates, and a gate-voltage-controlled inter-dot barrier to perform two-qubit gates by pulsed exchange coupling. We use this gate set to demonstrate a Bell state preparation between multielectron qubits with fidelity 90.3%, confirmed by two-qubit state tomography using spin parity measurements.
@article{arxiv.2008.03968,
title = {Bell-state tomography in a silicon many-electron artificial molecule},
author = {Ross C. C. Leon and Chih Hwan Yang and Jason C. C. Hwang and Julien Camirand Lemyre and Tuomo Tanttu and Wei Huang and Jonathan Y. Huang and Fay E. Hudson and Kohei M. Itoh and Arne Laucht and Michel Pioro-Ladrière and Andre Saraiva and Andrew S. Dzurak},
journal= {arXiv preprint arXiv:2008.03968},
year = {2021}
}