Centre for Quantum and Optical Sciences, ARC Centre of Excellence in Future Low-Energy Electronics Technologies, Swinburne University of Technology, Melbourne 3122, Australia.
Phys Rev Lett. 2018 Sep 21;121(12):120402. doi: 10.1103/PhysRevLett.121.120402.
We present an experimental investigation of collective oscillations in harmonically trapped Fermi gases through the crossover from two to three dimensions. Specifically, we measure the frequency of the radial monopole oscillation or breathing mode in highly oblate gases with tunable interactions. The breathing mode frequency is set by the adiabatic compressibility and probes the thermodynamic equation of state. In 2D, a dynamical scaling symmetry for atoms interacting via a δ potential predicts the breathing mode to occur at exactly twice the harmonic confinement frequency. However, a renormalized quantum treatment introduces a new length scale which breaks this classical scale invariance resulting in a so-called quantum anomaly. Our measurements deep in the 2D regime lie above the scale-invariant prediction for a range of interaction strengths providing evidence for the quantum anomaly and signifying the breakdown of an elementary δ-potential model of atomic interactions. By varying the atom number we can tune the chemical potential and see the breathing mode frequency evolve smoothly between the 2D to 3D thermodynamic limits.
我们通过从二维到三维的转变，对谐波囚禁费米气体中的集体振荡进行了实验研究。具体来说，我们通过可调相互作用测量了具有高扁度的气体的径向单极振荡或呼吸模式的频率。呼吸模式的频率由绝热压缩性确定，并探测热力学状态方程。在 2D 中，通过 δ 势相互作用的原子的动力学标度对称性预测呼吸模式恰好发生在谐波限制频率的两倍处。然而，重整化量子处理引入了一个新的长度标度，破坏了这种经典标度不变性，导致所谓的量子异常。我们在 2D 区域深处的测量结果高于相互作用强度范围内的标度不变预测，为量子异常提供了证据，并表明原子相互作用的基本 δ 势模型的失效。通过改变原子数，我们可以调节化学势，并看到呼吸模式频率在 2D 到 3D 热力学极限之间平滑演变。
