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Optical interferometric readout of a magnetically levitated superconducting microsphere

Jannek J. Hansen1,2,*, Stefan Minniberger2, Dominik Ilk1, Peter Asenbaum2, Gerard Higgins2,3, Rhys G. Povey2, Philip Schmidt2, Joachim Hofer2, Rémi Claessen1,2 et al.

Markus Aspelmeyer1,2 and Michael Trupke2,†

  • 1University of Vienna, Faculty of Physics, Vienna Center for Quantum Science and Technology, 1090 Vienna, Austria
  • 2Institute for Quantum Optics and Quantum Information (IQOQI) Vienna, Austrian Academy of Sciences, Boltzmanngasse 3, 1090 Vienna, Austria
  • 3Marietta Blau Institute for Particle Physics, Austrian Academy of Sciences, 1010 Vienna, Austria

  • *Contact author: jannek.hansen@univie.ac.at
  • †Contact author: michael.trupke@oeaw.ac.at
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Phys. Rev. Applied 25, 044080 – Published 28 April, 2026

DOI: https://doi.org/10.1103/ljxp-3f66

Abstract

We probe the motion of a 6-μg magnetically levitated superconducting microsphere using optical interferometry at 3K, achieving a resolution of the order of 1nm/Hz, and use the measured signal to feedback-cool its motion. The resolution exceeds the shot-noise limit of 11pm/Hz primarily due to technical noise arising from the roughness of the particle, in combination with its free rotation. These measurements demonstrate that the combination of interferometric optical readout and superconducting magnetic levitation, together with established techniques of cavity optomechanics, provides all the ingredients required for quantum physics experiments with microgram masses.

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Phys. Rev. Applied 25, 044080– Published 28 April, 2026
  • Received 8 August 2025
  • Revised 13 March 2026
  • Accepted 27 March 2026
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