Article

Quasiparticle Energy in a Strongly Interacting Homogeneous Bose-Einstein Condensate

Raphael LopesCavendish Laboratory, University of Cambridge, J. J. Thomson Avenue, Cambridge CB3 0HE, United KingdomChristoph EigenCavendish Laboratory, University of Cambridge, J. J. Thomson Avenue, Cambridge CB3 0HE, United KingdomAdam BarkerCavendish Laboratory, University of Cambridge, J. J. Thomson Avenue, Cambridge CB3 0HE, United KingdomKonrad ViebahnCavendish Laboratory, University of Cambridge, J. J. Thomson Avenue, Cambridge CB3 0HE, United KingdomMartin Robert-De-Saint-VincentCavendish Laboratory, University of Cambridge, J. J. Thomson Avenue, Cambridge CB3 0HE, United KingdomNir NavonCavendish Laboratory, University of Cambridge, J. J. Thomson Avenue, Cambridge CB3 0HE, United KingdomZoran HadzibabicCavendish Laboratory, University of Cambridge, J. J. Thomson Avenue, Cambridge CB3 0HE, United KingdomRobert P. SmithCavendish Laboratory, University of Cambridge, J. J. Thomson Avenue, Cambridge CB3 0HE, United Kingdom

2017en

ABI

Abstract

Using two-photon Bragg spectroscopy, we study the energy of particlelike excitations in a strongly interacting homogeneous Bose-Einstein condensate, and observe dramatic deviations from Bogoliubov theory. In particular, at large scattering length a the shift of the excitation resonance from the free-particle energy changes sign from positive to negative. For an excitation with wave number q, this sign change occurs at a≈4/(πq), in agreement with the Feynman energy relation and the static structure factor expressed in terms of the two-body contact. For a≳3/q we also see a breakdown of this theory, and better agreement with calculations based on the Wilson operator product expansion. Neither theory explains our observations across all interaction regimes, inviting further theoretical efforts.

Identifiers

DOI: 10.1103/physrevlett.118.210401

Citations and references

Cited by 20 references

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