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# Present status and future challenges of non-interferometric tests of collapse models

## Abstract

The superposition principle is the cornerstone of quantum mechanics, leading to a variety of genuinely quantum effects. Whether the principle applies also to macroscopic systems or, instead, there is a progressive breakdown when moving to larger scales is a fundamental and still open question. Spontaneous wavefunction collapse models predict the latter option, thus questioning the universality of quantum mechanics. Technological advances allow to increasingly challenge collapse models and the quantum superposition principle, with a variety of different experiments. Among them, non-interferometric experiments proved to be the most effective in testing these models. We provide an overview of such experiments, including cold atoms, optomechanical systems, X-ray detection, bulk heating and comparisons with cosmological observations. We also discuss avenues for future dedicated experiments, which aim at further testing collapse models and the validity of quantum mechanics.

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## Acknowledgements

We acknowledge fruitful discussions with R. Penrose and A. Vinante on various aspects of the models and related experiments. M.C. and M.P. are supported by UK EPSRC (grant no. EP/T028106/1). S.D. and A.B. acknowledge financial support from INFN. L.F., M.P., H.U. and A.B. acknowledge financial support from the H2020 FET Project TEQ (grant no. 766900). M.P. acknowledges the SFI-DfE Investigators Programme (grant no. 15/IA/2864), the Leverhulme Trust Research Project Grant UltraQute (grant no. RGP-2018-266), the Royal Society Wolfson Research Fellowship scheme (grant no. RSWF\R3\183013) and International Mobility Programme. H.U. acknowledges financial support from the Leverhulme Trust (grant no. RPG-2016-04) and EPSRC (grant no. EP/V000624/1). A.B. acknowledges the Foundational Questions Institute and Fetzer Franklin Fund, a donor advised fund of Silicon Valley Community Foundation (grant no. FQXi-RFP-CPW-2002), and the University of Trieste.

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Correspondence to Angelo Bassi.

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Carlesso, M., Donadi, S., Ferialdi, L. et al. Present status and future challenges of non-interferometric tests of collapse models. Nat. Phys. 18, 243–250 (2022). https://doi.org/10.1038/s41567-021-01489-5

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• DOI: https://doi.org/10.1038/s41567-021-01489-5

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