Die Separation for Mitigation of Phonon Bursts in Superconducting Circuits

TL;DR

This study demonstrates a die separation technique to block phonon propagation in superconducting circuits, reducing correlated errors caused by cosmic rays, with experimental validation using microwave detectors.

Contribution

We introduced a die separation method to mitigate phonon bursts in superconducting circuits and experimentally validated its effectiveness in blocking phonon propagation.

Findings

Successful detection of high-energy bursts with microwave detectors

Effective blocking of phonon propagation between dies

Observation of simultaneous events likely from cosmic particles

Abstract

Cosmic rays and background radioactive decay can deposit significant energy into superconducting quantum circuits on planar chips. This energy converts into pair-breaking phonons that travel across the substrate and generate quasiparticles, leading to correlated energy and phase errors in nearby qubits. To mitigate this, we fabricated two separate dies and placed them adjacently without a galvanic connection between them. This blocks phonon propagation from one die to the other. Using microwave kinetic inductance detectors on both dies, we successfully detected high-energy bursts and conclusively demonstrated the blocking effect. However, we also observed simultaneous events in both dies, likely from a single cosmic particle traversing both dies.