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-½ valence electron in its p- or d-orbital, respectively . These higher electron occupancies screen atomic-level disorder [3–5]. 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 .
|Publication status||Published - 2020 Aug 10|
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