Quantum fluctuations play a central role in the properties of quantum matter. In non-interacting ensembles, they manifest as fluctuations of non-commuting observables, quantified by Heisenberg inequalities1. In the presence of interactions, additional quantum fluctuations appear, from which many-body correlations and entanglement arise2. Weak interactions are predicted to deplete Bose–Einstein condensates by the formation of correlated pairs of bosons with opposite momenta3,4. Here we report the observation of these atom pairs in the depletion of an equilibrium interacting Bose gas5. Our measurements of atom–atom correlations, both at opposite and close-by momenta6,7, allow us to characterize the equilibrium many-body state. We also show that the atom pairs share the properties of two-mode squeezed states8,9, including relative number squeezing10,11,12. Our results illustrate how interacting systems acquire non-trivial quantum correlations as a result of the interplay between quantum fluctuations and interactions13.
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We thank A. Aspect, A. Browaeys, I. Carusotto, H. Cayla and T. Roscilde for their valuable comments on the manuscript, and acknowledge fruitful discussions with the members of the Quantum Gas group at Institut d’Optique. We acknowledge financial support from the LabEx PALM (grant number ANR-10-LABX-0039), the Région Ile-de-France in the framework of the DIM SIRTEQ, the ‘Fondation d’entreprise iXcore pour la Recherche’ and the Agence Nationale pour la Recherche (grant number ANR-17-CE30-0020-01). D.C. acknowledges support from the Institut Universitaire de France.
The authors declare no competing interests.
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Tenart, A., Hercé, G., Bureik, JP. et al. Observation of pairs of atoms at opposite momenta in an equilibrium interacting Bose gas. Nat. Phys. 17, 1364–1368 (2021). https://doi.org/10.1038/s41567-021-01381-2
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