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Two-level system hyperpolarization using a quantum Szilard engine

Nature Physics volume 19, pages 1320–1325 (2023)Cite this article

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Abstract

The innate complexity of solid-state physics exposes superconducting quantum circuits to interactions with uncontrolled degrees of freedom degrading their coherence. By implementing a quantum Szilard engine with an active feedback control loop, we show that a superconducting fluxonium qubit is coupled to a two-level system (TLS) environment of unknown origin, with a relatively long intrinsic energy relaxation time exceeding 50 ms. The TLSs can be cooled down, resulting in a four times lower qubit population, or they can be heated to manifest themselves as a negative-temperature environment corresponding to a qubit population of ~80%. We show that the TLSs and qubit are the dominant loss mechanism for each other and that qubit relaxation is independent of the TLS populations. Understanding and mitigating TLS environments is, therefore, not only crucial to improve the qubit lifetimes but also to avoid non-Markovian qubit dynamics.

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Fig. 1: Superconducting qubit, its environment and working principle of the Szilard engine.
Fig. 2: Szilard engine in action.
Fig. 3: Qubit evolution after running the Szilard engine.
Fig. 4: Measured population inversion and constant relaxation rate—signatures of the TLS environment.

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Data availability

Raw and processed data are publicly available via Zenodo at https://doi.org/10.5281/zenodo.7817552. Additional data are available from the corresponding authors upon reasonable request.

Code availability

The analysis script used to generate the data in the figures is publicly available via Zenodo at https://doi.org/10.5281/zenodo.7817552.

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Acknowledgements

We are grateful to J. Lisenfeld and W. Wulfhekel for insightful discussions as well as A. Lukashenko and L. Radtke for technical assistance. Funding was provided by the Alexander von Humboldt Foundation in the framework of a Sofja Kovalevskaja award endowed by the German Federal Ministry of Education and Research, and by the European Union’s Horizon 2020 programme under no. 899561 (AVaQus). M.S. and G.C. acknowledge support from the German Ministry of Education and Research (BMBF) within the project GEQCOS (FKZ: 13N15683 and 13N15685). P.P. acknowledges support from the German Ministry of Education and Research (BMBF) within the QUANTERA project SiUCs (FKZ: 13N15209). D.R., S.G. and W.W. acknowledge support from the European Research Council advanced grant MoQuOS (no. 741276). Facilities use was supported by the KIT Nanostructure Service Laboratory. We acknowledge qKit for providing a convenient measurement software framework.

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Authors and Affiliations

  1. PHI, Karlsruhe Institute of Technology, Karlsruhe, Germany

    Martin Spiecker, Patrick Paluch, Daria Gusenkova, Simon Günzler, Dennis Rieger, Ivan Takmakov, Patrick Winkel, Alexey V. Ustinov, Wolfgang Wernsdorfer & Ioan M. Pop

  2. IQMT, Karlsruhe Institute of Technology, Eggenstein-Leopoldshafen, Germany

    Martin Spiecker, Patrick Paluch, Nicolas Gosling, Daria Gusenkova, Simon Günzler, Dennis Rieger, Ivan Takmakov, Francesco Valenti, Patrick Winkel, Alexander Shnirman, Alexey V. Ustinov, Wolfgang Wernsdorfer & Ioan M. Pop

  3. Quantum Machines, Tel Aviv-Yafo, Israel

    Niv Drucker & Yonatan Cohen

  4. TKM, Karlsruhe Institute of Technology, Karlsruhe, Germany

    Shlomi Matityahu & Alexander Shnirman

  5. IPE, Karlsruhe Institute of Technology, Eggenstein-Leopoldshafen, Germany

    Richard Gebauer & Oliver Sander

  6. JARA Institute for Quantum Information (PGI-11), Forschungszentrum Jülich, Jülich, Germany

    Gianluigi Catelani

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Contributions

M.S. and I.M.P. conceived the experiment. N.D. and Y.C. installed and supervised the real-time microwave electronics. M.S. performed the experiment, analysed the data and developed the theoretical model. I.T. and P.W. designed and fabricated the parametric amplifier. R.G. and O.S. provided the real-time microwave electronics for preliminary experiments. P.P. and N.G. carried out additional measurements for the revised manuscript. M.S. and I.M.P. wrote the manuscript. A.S. and I.M.P. supervised the project. All authors discussed the results and contributed to the final manuscript.

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Correspondence to Martin Spiecker or Ioan M. Pop.

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Nature Physics thanks Tobias Lindström, Nathan Earnest-Noble and the other, anonymous, reviewer(s) for their contribution to the peer review of this work.

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Supplementary Sections A–M and Figs. 1–12.

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Spiecker, M., Paluch, P., Gosling, N. et al. Two-level system hyperpolarization using a quantum Szilard engine. Nat. Phys. 19, 1320–1325 (2023). https://doi.org/10.1038/s41567-023-02082-8

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