We report temperature measurements using a transmon qubit by detecting the population of its first three energy levels, after applying a sequence of π-pulses and performing projective dispersive readout. We measure the effective temperature of the qubit and characterize its relaxation and coherence times τ1,2 for three devices in the temperature range of 20−300 mK. We analyze the process of qubit thermalization to its effective environment consisting of multiple heat baths and support it with experimental data. Signal-to-noise (SNR) ratio of the temperature measurement depends strongly on τ1, which drops at higher temperatures due to quasiparticle excitations, adversely affecting the measurements and setting an upper bound of the dynamic temperature range of the thermometer. The measurement relies on coherent dynamics of the qubit during the π-pulses. The effective qubit temperature follows closely that of the cryostat in the range of 100−250 mK. We present a numerical model of the qubit population distribution and compare it favorably with the experimental results. Finally, we compare our technique with previous works on qubit thermometry and discuss its application prospects.
@article{arxiv.2409.02784,
title = {Thermometry Based on a Superconducting Qubit},
author = {Dmitrii S. Lvov and Sergei A. Lemziakov and Elias Ankerhold and Joonas T. Peltonen and Jukka P. Pekola},
journal= {arXiv preprint arXiv:2409.02784},
year = {2025}
}