Abstract

A vacuum is the gauge field state with the lowest energy and thus zero field strength. It is crucial to our understanding of some amazing features of particle structures and quantum fields. A familiar vacuum is the zero point fluctuation of the electromagnetic field, which leads to physical effects such as the Lamb shift and Casmir force. Notably, the vacuum of Abelian gauge field like electromagnetic field has been widely studied in various platforms and attracted a lot of interests. In sharp contrast, as firstly predicted in year 1975, vacua of the non-Abelian Yang-Mills field are a family of degenerate ground states with zero field strength but non-trivial topological structures. However, they have not been synthetized with any systems and are hard to be explored since they are typically nonperturbative solutions of a nonlinear quantum field equation. In this talk, the speaker would like to discuss the first theoretical proposal and experimental realization of a synthetic topological vacua with a cloud of atomic Bose-Einstein condensates. The vacuum of topological number n =1 and 2 are realized. Those different topology can be easily observed from their distinctive spin textures and Hopf links. The speaker and his research group expect their first trial would open a way to explore richer physics of non-Abelian gauge fields such as the behavior of instantons.

About the Speaker

Prof. ZHANG Shanchao obtained his PhD at the Hong Kong University of Science and Technology (HKUST) in 2013 and continued his research as a Postdoctoral Researcher at HKUST until 2017. He then joined South China Normal University (SCNU) and is currently an Associate Professor in the School of Physics and Telecommunication Engineering.

Prof. Zhang’s research focuses on the experimental studies of AMO physics like electromagnetically induced transparency (EIT), quantum memory, emergent topological gauge field physics and so on using ultracold atomic quantum gas of rubidium (Rb) and ytterbium (Yb) atoms. In his lab at SCNU, dilute atomic gas is laser cooled down with magneto-optical trap (MOT) and then further evaporatively cooled down to ~100 nano-Kelvin (nK) when the quantum wave-particle duality becomes significant. Techniques of coherently manipulating atomic quantum state with high quality are realized and a few interesting progress have been made in recent years, such as developing the most efficient quantum memory of single photon, demonstrating delta-quench measurement of quantum wave function and exploring the topology of non-Abelian vacua. He has received multiple research awards such as the 2013 Young Scientist Award of Hong Kong. 

For Attendees' Attention

This talk will be held online via Zoom. To attend, please join the Zoom meeting at https://hkust.zoom.us/j/95122774126 (Meeting ID: 951 2277 4126 / Passcode: 496108).

About the Center

For more information, please refer to the center website at https://iascqt.hkust.edu.hk/.