1/f Flux noise in Josephson phase qubits

Area of Science:

• Quantum Computing
• Condensed Matter Physics
• Metrology

Background:

• Josephson quantum bits (qubits) are fundamental to quantum computing.
• Understanding low-frequency noise (1/f noise) is crucial for qubit coherence.
• Existing methods struggle to accurately characterize noise below 1 Hz.

Purpose of the Study:

• To introduce a novel technique for measuring 1/f noise in Josephson qubits at frequencies below 1 Hz.
• To identify the dominant noise source in phase qubits.
• To compare experimental flux noise levels with theoretical predictions.

Main Methods:

• Development of a new measurement protocol for low-frequency noise spectra.
• Differential noise measurements on a phase qubit at positive and negative bias.
• Theoretical modeling of noise contributions from two-level state defects.

Main Results:

• The new method successfully measured low-frequency spectra below 1 Hz.
• Flux noise was identified as the dominant source, exceeding junction critical-current noise.
• Measured flux noise levels are inconsistent with the standard model of two-level state defect noise.

Conclusions:

• The developed method provides a new tool for characterizing qubit noise.
• Flux noise is a significant limiting factor in qubit performance.
• The standard model for surface oxide noise may require revision for superconducting qubits.