, , Yan Li, Chengjie Zhu
The Feynman relation 1, a much celebrated condensed matter physics gemstone for more than 70 years, predicts that the density excitation spectrum and structure factor of a condensed Bosonic system in the phonon regime drops linear and continuously to zero 2. Until now, this widely accepted monotonic excitation energy drop as the function of reduced quasi-momentum has never been challenged. We show rigorously that in a light-matter wave mixing process 3 in a Bosonic quantum gas 4, an optical-dipole potential arising from the internally-generated field can profoundly alter the Feynman relation and result in a new dynamic relation that exhibits an astonishing non-Feynman-like onset and cut-off in the excitation spectrum of the ground state energy. This is the first time that a nonlinear optical process is shown to actively and significantly alter the density excitation response of a quantum gas. Indeed, this dynamic relation with a non-Feynman onset and cut-off has no correspondence in either nonlinear optics of a normal gas or a phonon-based condensed matter Bogoliubov theory.
Nature - Scientific Reports
Bose condensate, condensed matter, Feynman relation