2012/03/31 by R. Mottl, F. Brennecke, K. Baumann +3 · 1 citation
Physics and Astronomy · #cond-mat.quant-gas #quant-ph
paper · pdf · doi:10.1126/science.1220314
published as Science 336, 1570 (2012) · 10 pages, 5 figures, supplementary materials
arxiv created 2012/09/28 · arxiv updated 2012/10/01
Long-range interactions in quantum gases are predicted to give rise to an excitation spectrum of roton character, similar to that observed in superfluid helium. We investigate the excitation spectrum of a Bose-Einstein condensate with cavity-mediated long-range interactions, which couple all particles to each other. Increasing the strength of the interaction leads to a softening of an excitation mode at a finite momentum, preceding a superfluid to supersolid phase transition. We study the mode softening spectroscopically across the phase transition using a variant of Bragg spectroscopy. The measured spectrum is in very good agreement with ab initio calculations and, at the phase transition, a diverging susceptibility is observed. The work paves the way towards quantum simulation of long-range interacting many-body systems.