Excitation of superconducting qubits from hot non-equilibrium quasiparticles

TL;DR

This paper investigates how hot non-equilibrium quasiparticles, with energies above the superconducting gap, influence superconducting qubits, revealing their potential as probes for dynamic quasiparticle energy distributions and their impact on qubit decoherence.

Contribution

The study introduces a model for hot quasiparticle effects on qubits and experimentally demonstrates their influence, challenging the assumption of thermal quasiparticle distributions.

Findings

Hot quasiparticles increase qubit excited state probability.

Experimental results agree with the non-thermal quasiparticle model.

Hot quasiparticles can be used to probe quasiparticle energy distributions.

Abstract

Superconducting qubits probe environmental defects such as non-equilibrium quasiparticles, an important source of decoherence. We show that "hot" non-equilibrium quasiparticles, with energies above the superconducting gap, affect qubits differently from quasiparticles at the gap, implying qubits can probe the dynamic quasiparticle energy distribution. For hot quasiparticles, we predict a non-neligable increase in the qubit excited state probability P_e. By injecting hot quasiparticles into a qubit, we experimentally measure an increase of P_e in semi-quantitative agreement with the model and rule out the typically assumed thermal distribution.