A Spin-Based Pathway to Testing the Quantum Nature of Gravity

• URL: http://arxiv.org/abs/2509.01586v1
• Date: Mon, 01 Sep 2025 16:18:46 GMT
• Title: A Spin-Based Pathway to Testing the Quantum Nature of Gravity
• Authors: Sougato Bose, Anupam Mazumdar, Roger Penrose, Ivette Fuentes, Marko Toroš, Ron Folman, Gerard J. Milburn, Myungshik Kim, Adrian Kent, A. T. M. Anishur Rahman, Cyril Laplane, Aaron Markowitz, Debarshi Das, Ethan Campos-Méndez, Eva Kilian, David Groswasser, Menachem Givon, Or Dobkowski, Peter Skakunenko, Maria Muretova, Yonathan Japha, Naor Levi, Omer Feldman, Damián Pitalúa-García, Jonathan M. H. Gosling, Ka-Di Zhu, Marco Genovese, Kia Romero-Hojjati, Ryan J. Marshman, Markus Rademacher, Martine Schut, Melanie Bautista-Cruz, Qian Xiang, Stuart M. Graham, James E. March, William J. Fairbairn, Karishma S. Gokani, Joseph Aziz, Richard Howl, Run Zhou, Ryan Rizaldy, Thiago Guerreiro, Tian Zhou, Jason Twamley, Chiara Marletto, Vlatko Vedral, Jonathan Oppenheim, Mauro Paternostro, Hendrik Ulbricht, Peter F. Barker, Thomas P. Purdy, M. V. Gurudev Dutt, Andrew A. Geraci, David C. Moore, Gavin W. Morley,
• Abstract summary: We propose an experiment to test the quantum nature of gravity by checking whether gravity can entangle two micron-sized crystals.<n>A pathway to this is to create macroscopic quantum superpositions of each crystal first using embedded spins and Stern-Gerlach forces.<n>This is based on extensive theoretical feasibility studies and experimental progress in quantum technology.
• Score: 2.052869256905295
• License: http://creativecommons.org/licenses/by-nc-nd/4.0/
• Abstract: A key open problem in physics is the correct way to combine gravity (described by general relativity) with everything else (described by quantum mechanics). This problem suggests that general relativity and possibly also quantum mechanics need fundamental corrections. Most physicists expect that gravity should be quantum in character, but gravity is fundamentally different to the other forces because it alone is described by spacetime geometry. Experiments are needed to test whether gravity, and hence space-time, is quantum or classical. We propose an experiment to test the quantum nature of gravity by checking whether gravity can entangle two micron-sized crystals. A pathway to this is to create macroscopic quantum superpositions of each crystal first using embedded spins and Stern-Gerlach forces. These crystals could be nanodiamonds containing nitrogen-vacancy (NV) centres. The spins can subsequently be measured to witness the gravitationally generated entanglement. This is based on extensive theoretical feasibility studies and experimental progress in quantum technology. The eventual experiment will require a medium-sized consortium with excellent suppression of decoherence including vibrations and gravitational noise. In this white paper, we review the progress and plans towards realizing this. While implementing these plans, we will further explore the most macroscopic superpositions that are possible, which will test theories that predict a limit to this.

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