Single-quasiparticle trapping in aluminum nanobridge Josephson junctions

Area of Science:

• Quantum computing and solid-state physics.
• Superconducting circuits and quantum information science.

Background:

• High quality factor superconducting resonators are crucial for quantum technologies.
• Trapped quasiparticles (QPs) are a significant source of decoherence in superconducting qubits.
• Understanding QP dynamics is essential for improving qubit performance and coherence times.

Purpose of the Study:

• To present microwave measurements of a superconducting resonator with Josephson junctions.
• To probe trapped quasiparticle number, energy distribution, and lifetimes.
• To validate models of quasiparticle transport and mitigation strategies.

Main Methods:

• Fabrication of a superconducting resonator with two aluminum nanobridge Josephson junctions in a loop, shunted by an on-chip capacitor.
• Utilizing microwave measurements to detect frequency shifts caused by trapped quasiparticles.
• Analyzing resonant frequency shifts to determine QP number, energy distribution, and lifetimes.
• Comparing experimental results with the Andreev bound state model.

Main Results:

• Trapped quasiparticle population was found to obey a Gibbs distribution above 75 mK.
• Non-Poissonian trapping statistics were observed.
• Experimental findings quantitatively agreed with the Andreev bound state model of transport.
• Demonstrated a practical method for quantifying on-chip QP populations in a cryogenic environment.

Conclusions:

• The study provides a practical method to quantify on-chip quasiparticle populations.
• Results validate the Andreev bound state model for quasiparticle transport.
• The findings offer insights into QP dynamics and inform strategies for mitigating decoherence in superconducting quantum devices.
• Demonstrated a method to validate QP mitigation strategies in cryogenic environments.