Publications by Robert Smith


Quasiparticle Energy in a Strongly Interacting Homogeneous Bose-Einstein Condensate.

Phys Rev Lett 118 (2017) 210401-

R Lopes, C Eigen, A Barker, KGH Viebahn, M Robert-de-Saint-Vincent, N Navon, Z Hadzibabic, RP Smith

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.


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