Quantum multicritical behavior is an elementary and central concept in the quantum phase transition. At quantum multicritical points, a number of phase transitions of different properties will become indistinguishable and at the same time, there will be distinct multicritical behaviors. Through many researches on this phenomenon, scientists have found many particular multicritical phenomena and novel quantum universality classes, which have advanced the understanding of quantum phase transition to a considerable extent. Although multicritical behavior is of great peculiarity and importance, scientists have encountered great difficulties in its experiments and observation. As for the universal behaviors near multicritical points, even greater difficulties are faced by the experimental research. In order to observe the universal behavior of multicritical phenomena, the system needs to be expanded to a sufficient size, while maintaining good maneuverability and reliability under noisy conditions, which, however, are difficult and even unfeasible in the experiment. Due to these difficulties, it is still experimentally impossible to observe universality classes and related critical behaviors, which are the core of multicritical behaviors.

Recently, under the guidance of Prof. Zhang Guofeng, doctoral student Zhu Hanjie from the School of Physics collaborated with researcher Liu Wuming from the Institute of Physics of Chinese Academy of Sciences to extend the multicritical phenomenon to the system of finite components and study how to detect the universal behavior at multicritical points in the noisy environment. Through introducing a staggered atomic bias structure, the multicritical behavior of a finite system can appear in the Dicke Model and the multicritical points can be described by a series of multicritical universality classes. Furthermore, an ion trap-based experimental scheme was proposed, which can enable the multicritical phenomenon with the finite size and multicritical phenomena to appear within the allowable range of experimental parameters. With the consideration of environmental noise, the results showed the possibility of revealing universality classes at the multicritical points and provided new clues for the research on multicritical behaviors. The work was published in Physical Review Letters on July 28. Doctoral student Zhu Hanjie is the first author and Prof. Zhang Guofeng is the corresponding author.

This work was supported by the General Program of National Natural Science Foundation of China, National Major Scientific, Funds for Instrument Development Project, Innovative Research Group Project, the Key R&D Program of The Ministry of Science and Technology, Pilot Project of the Chinese Academy of Sciences, etc.

Fig.1 Qubit-bosonic field system which can produce multicritical phenomena of finite components

Fig.2 Phase diagram of the system (a, c) and corresponding order parameters (b, d)

Fig. 3 Observation of multicritical universal behavior in the noisy environment (numerical simulation results)

More information is available at:

https://journals.aps.org/prl/pdf/10.1103/PhysRevLett.125.050402

Reported by Cai Hongyan

Reviewed by Li Guangchao

Edited by Sun Yecheng

Translated by Feng Yueyue