Theory of quasiparticle generation by microwave drives in superconducting qubits

TL;DR

This paper develops a theoretical framework to analyze how strong microwave drives in superconducting qubits can generate quasiparticles through multiphoton processes, potentially impacting qubit performance.

Contribution

It introduces a new theoretical model for calculating multiphoton-assisted quasiparticle generation rates in superconducting circuits under microwave drives.

Findings

Photon-assisted quasiparticle generation can occur at high drive powers.

Such quasiparticles may affect high-frequency readout and Floquet-engineered circuits.

Strong drives can induce pair-breaking processes previously assumed negligible.

Abstract

Microwave drives play a central role in the control of superconducting quantum circuits, enabling qubit gates, readout, and parametric interactions. As the drive frequencies are typically an order of magnitude smaller than (twice) the superconducting gap, it is generally assumed that such drives do not disturb the BCS ground state. However, sufficiently strong drives can activate multiphoton pair-breaking processes that generate quasiparticles (QPs) and result in qubit errors. In this work, we present a theoretical framework for calculating the rates of multiphoton-assisted pair-breaking transitions induced by charge- or flux-coupled microwave drives. Through illustrative examples, we show that photon-assisted QP generation may affect novel high-frequency dispersive readout architectures, as well as Floquet-engineered superconducting circuits operating under strong driving.