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

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.

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Cited by in corpus (18)

• Two-qubit silicon quantum processor with operation fidelity exceeding 99%
• Review of performance metrics of spin qubits in gated semiconducting nanostructures
• On-demand electrical control of spin qubits
• Fast Bayesian tomography of a two-qubit gate set in silicon
• Entanglement based observables for quantum impurities
• Non-reciprocal Pauli Spin Blockade in a Silicon Double Quantum Dot
• Single-tone pulse sequences and robust two-tone shaped pulses for three silicon spin qubits with always-on exchange
• Violating Bell's inequality in gate-defined quantum dots
• Designing globally optimal entangling gates using geometric space curves
• Path integral simulation of exchange interactions in CMOS spin qubits
• Robust entangling gate for capacitively coupled few-electron singlet-triplet qubits
• Quantum Computation by Spin Parity Measurements with Encoded Spin Qubits
• Theory on electron-phonon spin dehphasing in GaAs multi-electron double quantum dots
• Wavelet correlation noise analysis for qubit operation variable time series
• A diverse set of two-qubit gates for spin qubits in semiconductor quantum dots
• A SWAP Gate for Spin Qubits in Silicon
• Mapping Spin Interactions from Conductance Peak Splitting in Coulomb Blockade
• Exploring Entanglement Spectrum and Phase Diagram in multi-electron Quantum Dot Chains