Magnons at low excitations: observation of incoherent coupling to a bath of two-level systems

Pfirrmann, M., Boventer, I., Schneider, A., Wolz, T., Kläui, M., Ustinov, A. V. and Weides, M. (2019) Magnons at low excitations: observation of incoherent coupling to a bath of two-level systems. Physical Review Research, 1(3), 032023(R). (doi: 10.1103/PhysRevResearch.1.032023)

Abstract

Collective magnetic excitation modes, magnons, can be coherently coupled to microwave photons in the single excitation limit. This allows for access to quantum properties of magnons and opens up a range of applications in quantum information processing, with the intrinsic magnon linewidth representing the coherence time of a quantum resonator. Our measurement system consists of a yttrium iron garnet sphere and a three-dimensional microwave cavity at temperatures and excitation powers typical for superconducting quantum circuit experiments. We perform spectroscopic measurements to determine the limiting factor of magnon coherence at these experimental conditions. Using the input-output formalism, we extract the magnon linewidth κm. We attribute the limitations of the coherence time at lowest temperatures and excitation powers to incoherent losses into a bath of near-resonance two-level systems (TLSs), a generic loss mechanism known from superconducting circuits under these experimental conditions. We find that the TLSs saturate when increasing the excitation power from quantum excitation to multiphoton excitation and their contribution to the linewidth vanishes. At higher temperatures, the TLSs saturate thermally and the magnon linewidth decreases as well.

• Item Type: Articles
• Additional Information: This work was supported by the European Research Council (ERC) under the Grant Agreement No. 648011 and the Deutsche Forschungsgemeinschaft (DFG) within Project INST No. 121384/138-1 FUGG and SFB TRR 173. We acknowledge financial support by the Helmholtz International Research School for Teratronics (M.P. and T.W.) and the Carl-Zeiss-Foundation (A.S.). A.V.U. acknowledges partial support from the Ministry of Education and Science of Russian Federation in the framework of the Increase Competitiveness Program of the National University of Science and Technology MISIS (Grant No. K2-2017-081).
• Status: Published
• Refereed: Yes
• Glasgow Author(s) Enlighten ID: Weides, Professor Martin
• Authors: Pfirrmann, M., Boventer, I., Schneider, A., Wolz, T., Kläui, M., Ustinov, A. V., and Weides, M.
• College/School: College of Science and Engineering > School of Engineering > Electronics and Nanoscale Engineering
• Journal Name: Physical Review Research
• Publisher: American Physical Society
• ISSN: 2643-1564
• ISSN (Online): 2643-1564
• Published Online: 21 November 2019
• Copyright Holders: Copyright © 2019 American Physical Society
• First Published: First published in Physical Review Research 1(3):032023(R)
• Publisher Policy: Reproduced under a Creative Commons License