Lifetime and coherence of two-level defects in a Josephson junction

Area of Science:

• Quantum computing
• Solid-state physics
• Superconductivity

Background:

• Josephson phase qubits are a leading platform for quantum computation.
• Understanding decoherence mechanisms in qubits is crucial for improving quantum computer performance.
• Two-level defect states (TLSs) in qubit barriers can cause significant noise.

Purpose of the Study:

• To measure the lifetime (T₁) and coherence (T₂) of TLSs in Josephson phase qubit barriers.
• To investigate the relationship between TLS properties and their interaction strength with the qubit.
• To explain the observed T₁ and T₂ behaviors using a theoretical model.

Main Methods:

• Experimental measurement of T₁ and T₂ for TLSs in Josephson phase qubit barriers.
• Systematic variation of interaction strengths between TLSs and qubit systems.
• Theoretical modeling based on the standard TLS model, incorporating phonon-mediated dipole radiation and environmental fluctuations.

Main Results:

• Average decay times (T₁) exhibit a power-law dependence on interaction strengths.
• Average coherence times (T₂) show an optimal performance at intermediate coupling strengths.
• The standard TLS model successfully explains both T₁ and T₂ behaviors.

Conclusions:

• The interaction strength significantly influences qubit decoherence via TLSs.
• Coherence times are maximized at specific, intermediate coupling regimes.
• The standard TLS model provides a robust framework for understanding and mitigating decoherence in Josephson qubits.