Heralded state preparation in a superconducting qubit.

Area of Science:

• Quantum computing
• Superconducting circuits
• Quantum information science

Background:

• Superconducting qubits are essential for quantum computation.
• High-fidelity readout is critical for scalable quantum computers.
• Initialization and reset protocols are key challenges in qubit operation.

Purpose of the Study:

• To demonstrate high-fidelity, single-shot readout of a superconducting flux qubit.
• To implement a heralding protocol for improved qubit initialization.
• To explore a fast qubit reset method.

Main Methods:

• Utilized continuous measurement in the weak excitation regime.
• Implemented a heralding procedure to ensure initialization to the ground state.
• Analyzed pointer state distributions for fidelity assessment.

Main Results:

• Achieved single-shot readout fidelity below one part in 1000 resolution.
• Boosted readout fidelity to 93.9% using the heralding protocol.
• Suppressed errors caused by spurious thermal population.
• Demonstrated potential for a simple, fast qubit reset protocol.

Conclusions:

• High-fidelity readout and initialization are achievable with continuous measurement and heralding.
• The demonstrated techniques significantly improve superconducting qubit performance.
• This work contributes to the development of scalable quantum computing architectures.