Ozawa Hideki, Taie Shintaro, Ichinose Tomohiro, Takahashi Yoshiro
Department of Physics, Graduate School of Science, Kyoto University, Kyoto 606-8502, Japan.
Phys Rev Lett. 2017 Apr 28;118(17):175301. doi: 10.1103/PhysRevLett.118.175301. Epub 2017 Apr 25.
We report the momentum-resolved measurement of Bloch bands in an optical Lieb lattice for a Bose-Einstein condensate (BEC). A BEC in the lattice is transported to a desired quasimomentum by applying a constant force. The energy dispersion of the lowest band is obtained by integrating measured group velocities. We also measure the gap from the lowest band to the higher bands with the same quasimomentum, which can be extracted from the oscillation of the sublattice populations after preparing a superposition of the band eigenstates. We show that the experimental results agree with a band calculation based on the Bogoliubov approximation. It is revealed that the second band, which should be flat in a single-particle description, is shifted and, in particular, distorted around the Brillouin zone edge as the interaction strength increases.
我们报告了针对玻色 - 爱因斯坦凝聚体（BEC）在光学利布晶格中进行的布洛赫能带的动量分辨测量。通过施加恒定力，晶格中的BEC被传输到期望的准动量。最低能带的能量色散通过对测量的群速度进行积分得到。我们还测量了具有相同准动量时从最低能带到更高能带的能隙，该能隙可在制备能带本征态叠加后从亚晶格布居的振荡中提取。我们表明实验结果与基于博戈留波夫近似的能带计算相符。结果显示，在单粒子描述中应是平坦的第二能带，随着相互作用强度增加，在布里渊区边缘附近发生了移动，特别是出现了畸变。
