Recovery Dynamics of a Gap-Engineered Transmon after a Quasiparticle Burst.

Area of Science:

• Quantum computing
• Superconducting qubits
• Solid-state physics

Background:

• Ionizing radiation creates quasiparticle bursts in superconducting qubits.
• These bursts degrade qubit coherence, impacting quantum error correction.
• 3D gap-engineered transmon qubits are a promising platform for quantum computation.

Purpose of the Study:

• To experimentally investigate the impact of gap engineering on quasiparticle bursts in 3D transmon qubits.
• To understand the factors limiting the effectiveness of gap engineering.
• To identify strategies for mitigating quasiparticle-induced decoherence.

Main Methods:

• Continuous monitoring of qubit transitions to detect quasiparticle bursts.
• Utilizing 3D gap-engineered transmon qubits.
• Comparing burst detection rates in gap-engineered versus non-engineered qubits.
• Analyzing quasiparticle thermalization dynamics.

Main Results:

• Gap engineering reduced the quasiparticle burst detection rate by a factor of 5.
• The observed reduction was significantly less than theoretically expected.
• This discrepancy was attributed to slow phonon thermalization in the chip.
• Phonon thermalization times were found to be orders of magnitude longer than expected.

Conclusions:

• Gap engineering offers partial mitigation of quasiparticle bursts in superconducting qubits.
• Slow phonon thermalization is a critical bottleneck limiting the effectiveness of gap engineering.
• Addressing phonon dynamics is crucial for improving qubit coherence and quantum error correction.