Quasiparticle Dynamics in Superconducting Quantum-Classical Hybrid Circuits

TL;DR

This paper investigates how quasiparticles generated by SFQ circuits affect qubit coherence in superconducting hybrid systems, revealing phonon-mediated propagation as a key factor in QP dynamics and offering insights to mitigate QP poisoning.

Contribution

It provides the first detailed analysis of quasiparticle behavior in superconducting quantum-classical hybrid circuits involving SFQ and qubits, highlighting phonon-mediated QP propagation.

Findings

QP density peaks after several microseconds of SFQ operation

Phonon-mediated propagation dominates QP spreading

Insights for suppressing QP poisoning in hybrid systems

Abstract

Single flux quantum (SFQ) circuitry is a promising candidate for a scalable and integratable cryogenic quantum control system. However, the operation of SFQ circuits introduces non-equilibrium quasiparticles (QPs), which are a significant source of qubit decoherence. In this study, we investigate QP behavior in a superconducting quantum-classical hybrid chip that comprises an SFQ circuit and a qubit circuit. By monitoring qubit relaxation time, we explore the dynamics of SFQ-circuit-induced QPs. Our findings reveal that the QP density near the qubit reaches its peak after several microseconds of SFQ circuit operation, which corresponds to the phonon-mediated propagation time of QPs in the hybrid circuits. This suggests that phonon-mediated propagation dominates the spreading of QPs in the hybrid circuits. Our results lay the foundation to suppress QP poisoning in quantum-classical hybrid systems.