【报告题目】：Ultradilute Quantum Droplets

【报告人】：胡辉教授，斯威本科技大学量子技术理论中心

【报告时间】：2025年05月09日14:30

【报告地点】:腾讯会议：627-849-849

【报告摘要】：Over the past few years, a newly discovered phase of ultracold, dilute quantum droplets has attracted increasingly attention in different fields of physics. In sharp contrast to other gas-like phases in containers, quantum droplets are self-bound, liquid-like clusters of ten to hundred thousand of atoms in free space, formed by the delicate balance between the attractive mean-field force and repulsive force from quantum fluctuations.

I will report our theoretical progress on quantum droplets in two-component Bose-Bose mixtures. We revisit the Bogoliubov theory of quantum droplets proposed by Petrov [1], where the mean-field collapse is stabilized by the Lee-Huang-Yang quantum fluctuations. We show that a loophole in Petrov's theory, i.e., the ignorance of the softening complex Bogoliubov spectrum, can be naturally removed by the introduction of bosonic pairing [2]. The pairing leads to weaker mean-field attractions, and stronger Lee-Huang-Yang term in the case of unequal intraspecies interactions. As a result, the equilibrium density for the formation of self-bound droplets significantly decreases in the deep droplet regime, in agreement with a recent observation from diffusion Monte Carlo simulations. Our construction of a consistent pairing theory of ultradilute quantum droplet may also be relevant to understand the supersolid in dipolar gases. Furthermore, by considering both attractive two-body interaction and repulsive three-body interaction, we determine a rich phase diagram for three-body interacting droplets [3]. Most recently, we also find that the single-mode description necessarily breaks down in the deep droplet regime. This finding might provide a plausible microscopic explanation of the puzzling low critical particle number of quantum droplets, as experimentally observed [4].

References：

[1] D. S. Petrov, Phys. Rev. Lett. 115, 155302 (2015).

[2] H. Hu and X. -J. Liu, Phys. Rev. Lett. 125, 195302 (2020).

[3] H. Hu, Z. -Q. Yu, J. Wang, and X. -J. Liu, Phys. Rev. A 104, 043301 (2021).

[4] H. Hu, J. Wang, H. Pu, and X.-J. Liu, Phys. Rev. A 111, 023309 (2025).

【报告人简介】：胡辉1991年就读于清华大学，1996和2001年分别获得学士和博士学位。2001年到2004年先后在意大利国际理论物理中心，比萨高师和昆士兰大学从事博士后研究和学术访问。2006年到2008年任中国人民大学教授。2009年起在澳大利亚斯威本科技大学任教，先后获得澳大利亚基金委ARC QEII Fellowship（2009-2013），ARC Future Fellowship （2014-2017）和其他三项ARC Discovery Project项目资助，总额约250万澳元。2016年被选为美国物理学会会士。科研兴趣主要集中在量子流体理论和多体理论。现在胡辉是斯威本科技大学量子技术理论中心副教授，常务中心主任。