Phonon engineering of atomic-scale defects in superconducting quantum circuits

Area of Science:

• Solid-state physics
• Quantum computing
• Materials science

Background:

• Noise in low-temperature solid-state systems often originates from material defects.
• Tunneling two-level systems (TLS) model describes defects in amorphous materials.
• TLS are a primary limitation to coherence in superconducting quantum circuits.

Purpose of the Study:

• To directly modify the properties of TLS to mitigate their impact on quantum devices.
• To investigate the effect of suppressing microwave-frequency phonons on TLS coherence.
• To enhance the relaxation time of transmon qubits.

Main Methods:

• Fabrication of a system with an acoustic bandgap to suppress phonons at specific frequencies.
• Coupling TLS to a transmon qubit within the acoustic bandgap.
• Measurement of qubit relaxation time (T1) before and after bandgap creation.

Main Results:

• A pronounced increase in qubit relaxation time by two orders of magnitude was observed.
• The longest measured T1 time exceeded 5 milliseconds.
• Suppression of microwave-frequency phonons effectively altered TLS properties.

Conclusions:

• Creating an acoustic bandgap is a viable method for mitigating TLS noise in solid-state quantum systems.
• This approach allows for the study of highly coherent TLS.
• The findings offer new strategies for improving noise resilience in quantum computing hardware.