Abstract
Probing the possibility of entanglement generation through gravity offers a path to tackle the question of whether gravitational fields possess a quantum mechanical nature. A potential realization necessitates systems with low-frequency dynamics at an optimal mass scale, for which the microgram-to-milligram range is a strong contender. Here, after refining a figure-of-merit for the problem, we present a 1-milligram torsional pendulum operating at 18 Hz. We demonstrate laser cooling its motion from room temperature to 240 microkelvins, surpassing by over 20-fold the coldest motions attained for oscillators ranging from micrograms to kilograms. We quantify and contrast the utility of the current approach with other platforms. The achieved performance and large improvement potential highlight milligram-scale torsional pendulums as a powerful platform for precision measurements relevant to future studies at the quantum-gravity interface.
Data availability
The numerical source data, as well as datasets generated during and/or analyzed during this study, are available in ISTA Research Explorer https://research-explorer.ista.ac.at/record/20842.
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Acknowledgements
We thank Gerard Higgins, Andrei Militaru, Nikolai Kiesel, and Markus Aspelmeyer for useful discussions on the topic of the figure-of-merit. We thank Teodor Strömberg for helping with the additional characterizations of the optical lever noise. We thank Johannes Fink and Scott Waitukaitis for their helpful feedback on the manuscript. This work was supported by Institute of Science and Technology Austria and the European Research Council under Grant No. 101087907 (ERC CoG QuHAMP).
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O.H. conceived the experiment and supervised the project. M.M. manufactured the pendulum. S.A. and P.R. built the experimental setup. S.A. and O.H. performed the reported experiments, analyzed the data, and wrote the article.
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Agafonova, S., Rosselló, P., Mekonnen, M. et al. One-milligram torsional pendulum toward experiments at the quantum-gravity interface. Commun Phys (2026). https://doi.org/10.1038/s42005-026-02514-w
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DOI: https://doi.org/10.1038/s42005-026-02514-w
