Thermometry based on a superconducting qubit

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School of Science | Doctoral thesis (article-based) | Defence date: 2026-01-20
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Authors

Date

2026

Department

Teknillisen fysiikan laitos
Department of Applied Physics

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Mcode

Degree programme

Language

en

Pages

150 + app. 80

Series

Aalto University publication series Doctoral Theses, 28/2026

Abstract

In this thesis, we demonstrate the operation of a thermometer based on a superconducting transmon qubit. We experimentally show that by measuring the qubit’s population distribution and its respective effective temperature, it is possible to measure temperature of an object with which the qubit is thermalized. However, due to the qubit’s quantum nature, it is very sensitive to any other source of excitation present in the system, which can be treated as a separate noise source or a heat bath. Consideration of a qubit coupled to several uncorrelated noise sources constitutes an important part of the thesis. We investigate the applicability range of the qubit thermometer in terms of dynamic range, operation speed and precision. While the upper bound on the dynamic temperature range is mainly defined by the material properties of the superconductor used in the qubit fabrication, namely, by the superconducting gap, the lower temperature is set by coupling to parasitic excitation sources. The population measurements of a transmon qubit are based on an algorithm which uses π-pulses for swapping the populations of the three lowest energy levels of the transmon. The largest impact on the precision of the measurement is defined by the signal-to-noise ratio and the quality of the qubit control pulses. The precision limit is ultimately defined by the quantum Cramér-Rao bound, highlighting the statistical origin of this thermometry method. Finally, we utilize the transmon qubit for thermometry of a mesoscopic heat bath located on the same chip. The heat bath is a normal metal resistor, whose temperature was controlled with normal metal/insulator/superconductor (NIS) junctions. By coupling the transmon to the resistor capacitively and performing the population measurements, we could observe linear dependence between the qubit effective temperature and the temperature of the resistor. Moreover, while the designed mechanism of the qubit-resistor coupling was photonic, we managed to observe another channel of interaction. At large bias voltages applied to the NIS-junction, which sets the temperature of the resistor, the junction starts to emit nonequilibrium phonons that can break Cooper pairs in the superconducting qubit. This is a nonlocal effect, in which nonequilibrium quasiparticles lead both to change of the qubit population distribution and significant suppression of the relaxation time.

Description

Supervising professor

Pekola, Jukka P., Prof., Aalto University, Department of Applied Physics, Finland

Thesis advisor

Peltonen, Joonas T., Dr., Aalto University, Finland

Keywords

quantum sensing, quantum thermometry, quantum thermodynamics, quantum electrodynamics, superconducting qubits

Other note

Parts

  • [Publication 1]: Azat Gubaydullin, George Thomas, Dmitry S. Golubev, Dmitrii Lvov, Joonas T. Peltonen and Jukka P. Pekola. Photonic heat transport in three terminal superconducting circuit. Nature Communications, 13:1552, 10 pages, March 2022.
    Full text in Acris/Aaltodoc: https://urn.fi/URN:NBN:fi:aalto-202204282962
    DOI: 10.1038/s41467-022-29078-x View at publisher
  • [Publication 2]: S. A. Lemziakov, B. Karimi, S. Nakamura, D. S. Lvov, R. Upadhyay, C. D. Satrya, Z.-Y. Chen, D. Subero, Y.-C. Chang, L. B. Wang, J. P. Pekola. Applications of Superconductor–Normal Metal Interfaces. Journal ofLow Temperature Physics, 20 pages, 217:54-81, 28 pages, May 2024.
    Full text in Acris/Aaltodoc: https://urn.fi/URN:NBN:fi:aalto-202410306982
    DOI: 10.1007/s10909-024-03144-8 View at publisher
  • [Publication 3]: Steve Campbell, Irene D’Amico, Mario A. Ciampini, Janet Anders, Natalia Ares, Simone Artini, Alexia Auffeves, Lindsay Bassman Oftelie, Laetitia P. Bettmann, Marcus V. S. Bonanca, Thomas Busch, MicheleCampisi, Moallison F. Cavalcante, Luis A. Correa, Eloisa Cuestas, Ceren B. Dag, Salambo Dago, Sebastian Deffner, Adolfo Del Campo, Andreas Deutschmann-Olek, Sandro Donadi, Emery Doucet, Cyril Elouard, Klaus Ensslin, Paul Erker, Nicole Fabbri, Federico Fedele, Guilherme Fiusa, Thomas Fogarty, Joshua Folk, Giacomo Guarnieri, Abhaya S. Hegde, Santiago Hernandez-Gomez, Chang-Kang Hu, Fernando Iemini, Bayan Karimi, Nikolai Kiesel, Gabriel T. Landi, Aleksander Lasek, Sergei Lemziakov, Gabriele Lo Monaco, Eric Lutz, Dmitrii Lvov, Olivier Maillet, Mohammad Mehboudi, Taysa M. Mendonca, Harry J. D. Miller, Andrew K. Mitchell, Mark T. Mitchison, Victor Mukherjee, Mauro Paternostro, Jukka Pekola, Marti Perarnau-Llobet, Ulrich Poschinger, Alberto Rolandi, Dario Rosa, Rafael Sanchez, Alan C. Santos, Roberto S. Sarthour, Eran Sela, Andrea Solfanelli, Alexandre M. Souza, Janine Splettstoesser, Dian Tan, Ludovico Tesser, Tan Van Vu, Artur Widera, Nicole Yunger Halpern, Krissia Zawadzki. Roadmap on Quantum Thermodynamics. Accepted for publication in Quantum Science and Technology, 64 pages, November 2025.
    DOI: 10.1088/2058-9565/ae1e27 View at publisher
  • [Publication 4]: Dmitrii S. Lvov, Sergei A. Lemziakov, Elias Ankerhold, Joonas T. Peltonen, and Jukka P. Pekola. Thermometry Based on a Superconducting Qubit. Physical Review Applied, 23(5), 054079, May 2025.
    Full text in Acris/Aaltodoc: https://urn.fi/URN:NBN:fi:aalto-202506114496
    DOI: 10.1103/PhysRevApplied.23.054079 View at publisher

Citation

Permanent link to this item

https://urn.fi/URN:ISBN:978-952-64-2959-5

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[diss] Perustieteiden korkeakoulu / SCI