Robust and localised control of a 10-spin qubit array in germanium.

Area of Science:

• Quantum Computing
• Solid-State Physics
• Materials Science

Background:

• Quantum computers rely on high-fidelity qubit operations.
• Germanium-based qubits utilizing hole spins offer fast, electric-field-controlled gates via spin-orbit interaction.
• Challenges include g-tensor anisotropy and sensitivity, hindering scalability.

Purpose of the Study:

• Investigate a 10-spin qubit array in germanium for scalable quantum computing.
• Optimize qubit control and reduce crosstalk in large qubit arrays.
• Understand the mechanisms behind qubit uniformity and control.

Main Methods:

• Fabrication and characterization of a two-dimensional 10-spin qubit array.
• Measurement of single-qubit gate fidelities.
• Tuning of hole occupation to control spin susceptibility.
• Rabi frequency measurements for plunger gate driving.
• Probing electric dipole spin resonance locality and crosstalk.

Main Results:

• Achieved single-qubit gate fidelities exceeding 99% with uniform qubit properties.
• Demonstrated control over spin susceptibility by tuning hole occupation.
• Obtained high Rabi frequencies (>1.45 MHz/(mV·T)) for plunger gate driving.
• Reduced crosstalk by a factor of 2.5 using three-hole occupancy compared to single-hole occupancy.
• Theoretical modeling identified p-orbital anisotropy and Coulomb interactions as key mechanisms.

Conclusions:

• High-fidelity and uniform qubit properties are achievable in germanium hole spin systems.
• Quantum dot plunger gate configurations can significantly reduce crosstalk, enhancing scalability.
• Understanding orbital anisotropy and Coulomb interactions is crucial for reproducible control of large qubit arrays.