Readout-induced degradation of transmon lifetimes: interplay of TLSs and qubit spectral reshaping

TL;DR

This paper investigates how measurement backaction degrades transmon qubit lifetimes during dispersive readout, revealing the roles of TLS interactions and spectral reshaping, and offers practical guidelines for optimizing readout protocols.

Contribution

It combines theoretical modeling and experimental validation to understand readout-induced qubit lifetime degradation caused by TLSs and spectral effects, providing practical optimization strategies.

Findings

Driving at the resonator frequency minimizes lifetime degradation.

Qubit emission spectrum becomes non-Lorentzian with readout drive.

Theoretical predictions match experimental measurements quantitatively.

Abstract

Measurement backaction degrades dispersive readout of superconducting qubits even at modest drive strengths, often via the reduction of qubit lifetimes during readout. In this work, we theoretically and experimentally study this degradation and show how it can result from the interplay between detuned two-level systems (TLSs) and a drive-renormalized qubit spectrum. For modest to strong readout, the qubit emission spectrum becomes non-Lorentzian and depends sensitively on the readout drive frequency (even when measurement rate is fixed). We combine the readout-modified qubit emission spectrum with time-dependent perturbation theory to predict qubit lifetimes in the presence of a TLS bath. Master equation simulations and experimental measurements on a frequency-tunable transmon confirm these predictions quantitatively. In particular, we find that driving at the resonator frequency associated with the qubit ground state yields the narrowest qubit emission spectrum and the least lifetime degradation for a fixed measurement rate, providing a practical guideline for optimizing readout protocols in future quantum processors.