Dimensionality plays an essential role in determining the nature of quantum gases. Fruitful physics may appear at the low and crossover dimensions. In the current generation of cold atom experiments, the dimensionality of the system can be controlled by optical lattices. In this talk, I will firstly present our results about ultracold bosons in shallow low-dimensional quasiperiodic potentials [1,2]. We study the critical localization properties and fractality in the non-interacting case [1]. Based on these results, we move to the interacting cases and find Bose glass surrounded by superfluid and Mott phases [2]. At finite temperature, we show that the melting of the Mott lobes is characteristic of a fractal structure and find that the Bose glass is robust against thermal fluctuations up to temperatures accessible in experiments. Recently, we also carry out experimental measurement of the Mott transition and find the delocalization effect induced by disorder[3]. In the second part, I will report our recent study of strongly-interacting bosons at 2D-1D dimensional crossover [4,5]. We find the single-particle correlation function of the system evolves from a Berezinskii-Kosterlitz-Thouless (BKT) form to a Tomonaga-Luttinger liquid (TLL) type [5]. Also, we perform thermometry on the low dimensional bosons with 1 nK sensitivity and observe an anomalous cooling effect at the dimensional reduction [6], which we interpret using the entropy picture. Finally, I will discuss potential outlooks based on these studies.

References

[1]. H. Yao et al, Phys. Rev. Lett. 123(7), 070405 (2019)
[2]. H. Yao et al, Phys. Rev. Lett. 125(6), 060401 (2020)
[3]. H. Yao et al, Phys. Rev. Lett. 133(12), 123401 (2024)
[4]. H. Yao et al, SciPost Phys. 15, 050 (2023)
[5]. Y. Guo et al, Nature Physics 20, 934–938 (2024)
[6]. Y. Guo et al, Science Advances, 10(7), eadk6870 (2024)

 

Biosketch

Hepeng Yao is a postdoc researcher in the group of Prof. Thierry Giamarchi from the University of Geneva. He did his bachelor in Peking University (China). In 2020, he received his PhD from Ecole Polytechnique (France) under the supervision of Prof. Laurent Sanchez-Palencia. He received “CSC Award for outstanding self-financed students abroad” in 2020, and French DIM-SIRTEQ PhD grant in 2017. His main research interest is the theory of ultracold atom and quantum simulation, as well as their connection with experiments. Specifically, he mainly works on the properties of low dimensional quantum gas, which includes localization in quasiperiodic systems, dimensional crossover and etc. He is mainly working with advanced numerical techniques such as quantum Monte Carlo. He is an author of 6 theoretical paper in “Physical Review Letter”, where he is the first author for 3 of them. Also, he is a Referee for the “Physical Reviews” journals.

Please contact phweb@ust.hk should you have questions about the talk.