Institute for Space Sciences, Bucharest-Măgurele, R 077125 Romania.
Fakultät für Mathematik und Naturwissenschaften, Bergische Universität Wuppertal, 42097 Wuppertal, Germany.
Phys Rev Lett. 2018 Jun 15;120(24):243402. doi: 10.1103/PhysRevLett.120.243402.
We investigate the universal thermodynamics of the two-component one-dimensional Bose gas with contact interactions in the vicinity of the quantum critical point separating the vacuum and the ferromagnetic liquid regime. We find that the quantum critical region belongs to the universality class of the spin-degenerate impenetrable particle gas which, surprisingly, is very different from the single-component case and identify its boundaries with the peaks of the specific heat. In addition, we show that the compressibility Wilson ratio, which quantifies the relative strength of thermal and quantum fluctuations, serves as a good discriminator of the quantum regimes near the quantum critical point. Remarkably, in the Tonks-Girardeau regime, the universal contact develops a pronounced minimum, reflected in a counterintuitive narrowing of the momentum distribution as we increase the temperature. This momentum reconstruction, also present at low and intermediate momenta, signals the transition from the ferromagnetic to the spin-incoherent Luttinger liquid phase and can be detected in current experiments with ultracold atomic gases in optical lattices.
我们研究了在真空和铁磁液态之间的量子临界点附近具有接触相互作用的二维玻色气体的普遍热力学性质。我们发现，量子临界点区域属于自旋简并不可穿透粒子气体的普遍类，这令人惊讶地与单一组分情况不同，并确定了其与比热峰的边界。此外，我们还表明，压缩系数威尔逊比（衡量热和量子涨落相对强度的指标）是量子临界点附近量子态的良好鉴别器。值得注意的是，在 Tonks-Girardeau 区域，普遍接触出现了明显的最小值，这反映在随着温度升高，动量分布的反直觉变窄。这种动量重构在低动量和中间动量下也存在，标志着从铁磁态到自旋非相干 Luttinger 液体相的转变，并且可以在当前使用光学晶格中的超冷原子气体进行的实验中检测到。
