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Quantum Geometry and Flat Band Bose-Einstein Condensation
Aleksi Julku1,2, Georg M Bruun2,3, Päivi Törmä1
1Department of Applied Physics, Aalto University, P.O. Box 15100, 00076 Aalto, Finland.
Abstract:
We study the properties of a weakly interacting Bose-Einstein condensate (BEC) in a flat band lattice system by using the multiband Bogoliubov theory and discover fundamental connections to the underlying quantum geometry. In a flat band, the speed of sound and the quantum depletion of the condensate are dictated by the quantum geometry, and a finite quantum distance between the condensed and other states guarantees stability of the BEC. Our results reveal that a suitable quantum geometry allows one to reach the strong quantum correlation regime even with weak interactions.
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