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

Area of Science:

• Quantum computing
• Solid-state physics
• Nanotechnology

Background:

• Scalable quantum processors require millions of qubits, favoring nanoscale devices like silicon quantum dots.
• Atomic-level disorder in nanoscale devices degrades quantum dot uniformity and performance.
• Spin qubits in silicon quantum dots are promising candidates for quantum information processing.

Purpose of the Study:

• To investigate the use of multielectron spin qubits in silicon double quantum dots to mitigate disorder effects.
• To demonstrate a universal gate set for high-fidelity quantum operations on these qubits.
• To achieve high-fidelity entanglement between multielectron qubits.

Main Methods:

• Utilizing silicon double quantum dots with high electron occupancy (5 or 13 electrons) to form spin qubits.
• Employing a micromagnet for electrically driven single-qubit gates via magnetic field gradients.
• Implementing two-qubit gates through pulsed exchange coupling controlled by an inter-dot barrier.
• Performing two-qubit state tomography using spin parity measurements for fidelity confirmation.

Main Results:

• Demonstrated robust spin qubits in silicon double quantum dots with screened disorder effects due to high electron occupancy.
• Implemented a universal gate set for single and two-qubit operations.
• Achieved a Bell state preparation fidelity of 90.3% between multielectron qubits.
• Confirmed fidelity through spin parity measurements and two-qubit state tomography.

Conclusions:

• Multielectron silicon quantum dot spin qubits effectively screen atomic-level disorder, enhancing uniformity.
• The demonstrated universal gate set and high-fidelity entanglement are critical steps towards scalable quantum processors.
• This approach offers a viable pathway for building robust and scalable silicon-based quantum computers.