Lopes Raphael, Eigen Christoph, Barker Adam, Viebahn Konrad G H, Robert-de-Saint-Vincent Martin, Navon Nir, Hadzibabic Zoran, Smith Robert P
Cavendish Laboratory, University of Cambridge, J. J. Thomson Avenue, Cambridge CB3 0HE, United Kingdom.
Phys Rev Lett. 2017 May 26;118(21):210401. doi: 10.1103/PhysRevLett.118.210401. Epub 2017 May 23.
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.
利用双光子布拉格光谱，我们研究了强相互作用均匀玻色 - 爱因斯坦凝聚体中类粒子激发的能量，并观察到与博戈留波夫理论的显著偏差。特别是，在大散射长度(a)时，激发共振相对于自由粒子能量的偏移从正号变为负号。对于波数为(q)的激发，这种符号变化发生在(a≈4/(πq))处，这与费曼能量关系以及用两体接触表示的静态结构因子一致。对于(a≳3/q)，我们还看到该理论的失效，并且与基于威尔逊算符乘积展开的计算结果更相符。两种理论都无法解释我们在所有相互作用区域的观测结果，这促使进一步开展理论研究。
