Bell-state tomography in a silicon many-electron artificial molecule

TL;DR

This paper demonstrates high-fidelity Bell state preparation in silicon double quantum dots with multielectron qubits, leveraging their robustness against atomic disorder and implementing universal gates for quantum computing.

Contribution

It introduces a method for Bell-state tomography in silicon many-electron artificial molecules, showing high-fidelity entanglement using a novel multielectron qubit approach.

Findings

Achieved 90.3% Bell state fidelity.

Implemented universal single and two-qubit gates.

Multielectron qubits screen atomic disorder effectively.

Abstract

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-$\frac{1}{2}$ 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.