Quantum control and process tomography of a semiconductor quantum dot hybrid qubit

Area of Science:

• Quantum Computing
• Semiconductor Physics
• Quantum Information Science

Background:

• Semiconductor quantum dots are promising platforms for quantum bits (qubits) due to similarities with microelectronic transistors.
• Existing quantum dot spin qubits offer long coherence but suffer from slow manipulation speeds, hindering applications like factoring.
• Simpler qubit designs are desirable for enhanced scalability and manufacturability in quantum computing.

Purpose of the Study:

• To demonstrate a novel hybrid spin-charge qubit in semiconductor quantum dots.
• To achieve faster qubit manipulation speeds compared to existing double-dot qubits.
• To develop a simple, scalable qubit requiring minimal external components like micromagnets or nuclear-spin preparation.

Main Methods:

• Fabrication of a hybrid spin-charge qubit utilizing semiconductor quantum dots.
• Electrical control of the qubit for manipulation and state readout.
• Characterization of qubit performance using full process tomography.

Main Results:

• Demonstration of a hybrid qubit enabling fast rotations about two Bloch sphere axes.
• Achieved π-rotation times below 100 picoseconds, over an order of magnitude faster than previous double-dot qubits.
• High fidelities obtained: 85% for X rotations and 94% for Z rotations.

Conclusions:

• The hybrid spin-charge qubit offers a significant speed enhancement for quantum information processing.
• The qubit's design combines charge-like speed with spin-like coherence, operating effectively over a broad gate voltage range.
• This advancement represents a crucial step towards practical and scalable quantum computers.