Proposal for a Bell Test with Entangled Atoms of Different Mass

X. T. Yan; S. Kannan; Y. S. Athreya; A. G. Truscott; S. S. Hodgman

doi:10.22331/q-2025-12-11-1939

Proposal for a Bell Test with Entangled Atoms of Different Mass

X. T. Yan, S. Kannan, Y. S. Athreya, A. G. Truscott, and S. S. Hodgman

Research School of Physics, Australian National University, Canberra 2601, Australia

Published:	2025-12-11, volume 9, page 1939
Editor:	Mark Mitchison
Eprint:	arXiv:2411.08356v4
Doi:	https://doi.org/10.22331/q-2025-12-11-1939
Citation:	Quantum 9, 1939 (2025).

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Abstract

We propose a Bell test experiment using momentum-entangled atom pairs of different masses, specifically metastable helium isotopes ${}^{3}He^{*}$ and ${}^{4}He^{*}$, though the method extends to other atom species. Entanglement is generated via collisions, after which the quantum states are manipulated using two independent atom interferometers, enabling precise phase control over each species. Numerical simulations predict a significant violation of Bell's inequality under realistic conditions. This proposal opens a new paradigm to study the intersection of quantum mechanics and gravity.

Featured image: Schematic of our proposed experiment to test Bell inequality violations between atoms of different masses. (a) Clouds of helium-3 (red) and helium-4 (blue) atoms are prepared, with a laser putting the helium-4c atoms into a superposition of up and down momentum states. (b) Collisions between the clouds generate expanding “halos” of entangled atom pairs, creating quantum correlation between the momenta of the two isotopes. (c) Additional laser pulses act as atomic matter-wave mirrors and beam-splitters to mix the atomic paths. (d) The final momentum distribution allows us to measure correlations that would violate Bell’s inequality, direct evidence of non-local quantum behaviour in massive particles.

Popular summary

Quantum entanglement reveals surprising correlations between particles that defy classical explanations. An experimental technique called a Bell test is designed to distinguish these quantum correlations. However, such tests have so far predominantly been performed with photons or the internal states of atoms. Our work introduces a new method to conduct a Bell test using atoms of different masses, specifically two isotopes of helium, thereby pushing quantum mechanics into new regimes of massive particles.

We generate pairs of entangled momenta by inducing controlled collisions between ultracold helium-3 and helium-4 atoms. Because the entangled pairs involve 2 different mass atoms, this process creates a “mass-entangled” state – a unique quantum superposition where different masses traversing different paths. Following this, we use laser pulses tuned to each isotope's specific transition frequency to control the momentum and phase of each type of atom independently. This independent manipulation allows us to set up a Bell test in a way that was not possible with atoms of the same isotope. Our theoretical modelling and numerical simulations indicate a significant violation of Bell’s inequality under realistic experimental conditions should be possible.

This work opens exciting possibilities for exploring the intersections between quantum mechanics and gravity. Entangling atoms of different masses introduces intriguing questions regarding how these quantum states influence gravity from the perspective of general relativity. Upcoming experiments could investigate these effects, offering insights into the unification of quantum mechanics and gravity, and providing new constraints on models in which gravity or spacetime fluctuations gradually destroy quantum coherence.

► BibTeX data

@article{Yan2025proposalbelltest,
  doi = {10.22331/q-2025-12-11-1939},
  url = {https://doi.org/10.22331/q-2025-12-11-1939},
  title = {Proposal for a {B}ell {T}est with {E}ntangled {A}toms of {D}ifferent {M}ass},
  author = {Yan, X. T. and Kannan, S. and Athreya, Y. S. and Truscott, A. G. and Hodgman, S. S.},
  journal = {{Quantum}},
  issn = {2521-327X},
  publisher = {{Verein zur F{\"{o}}rderung des Open Access Publizierens in den Quantenwissenschaften}},
  volume = {9},
  pages = {1939},
  month = dec,
  year = {2025}
}

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Cited by

[1] Y. S. Athreya, S. Kannan, X. T. Yan, R. J. Lewis-Swan, K. V. Kheruntsyan, A. G. Truscott, and S. S. Hodgman, "Bell correlations between momentum-entangled pairs of 4He* atoms", Nature Communications 17 1, 2357 (2026).

[2] S. Kannan, Y. S. Athreya, A. H. Abbas, X. T. Yan, S. S. Hodgman, and A. G. Truscott, "Measurement of the <inline-formula><mml:math><mml:mi>s</mml:mi></mml:math></inline-formula>-wave scattering length between metastable helium isotopes", Physical Review A 110 6, 063324 (2024).

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