A dressed singlet-triplet qubit in germanium.

Area of Science:

• Quantum Computing
• Semiconductor Physics
• Spintronics

Background:

• Semiconductor hole spin qubits offer long coherence times at low magnetic fields but suffer from slow gate speeds.
• Singlet-triplet (ST) qubits maintain high gate speeds via exchange interaction (J) but are sensitive to charge noise at large J.
• Operating ST qubits at low magnetic fields and low exchange interactions presents a challenge for balancing coherence and control.

Purpose of the Study:

• To demonstrate a highly coherent ST hole spin qubit in germanium operating at low magnetic fields and low exchange interactions.
• To achieve high-fidelity quantum gate operations and extend qubit coherence times.
• To explore methods for robust quantum control in semiconductor qubits.

Main Methods:

• Fabrication and characterization of a germanium ST hole spin qubit.
• Modulation of the exchange interaction (J) for resonant driving of the ST qubit.
• Implementation of frequency modulation for universal quantum control.
• Realization of a dressed ST qubit by continuous resonant drive.

Main Results:

• Achieved an average gate fidelity of 99.68% and a coherence time (T*₂) of 1.9 μs at low magnetic field and low exchange interaction.
• Demonstrated a tenfold increase in coherence time (T*_2ρ) to 20.3 μs for the dressed ST qubit.
• Attained an average gate fidelity of 99.63% using frequency modulation for universal control.

Conclusions:

• Germanium ST qubits can achieve high coherence times and high-fidelity control simultaneously, even at low magnetic fields and exchange interactions.
• Resonant driving and dressing techniques significantly enhance qubit coherence.
• The demonstrated control methods pave the way for efficient semiconductor-based quantum processors.