Source: China University of Science and Technology News

The team of Academician Guo Guangcan of our University has made important experimental progress in quantum simulation based on artificial synthetic dimensions. In this team, Li Chuanfeng, Xu Jinshi, Han Yongjian and others bound photons with different orbital angular momenta (also known as vortex photons) in a degenerate optical resonator, and artificially synthesized a one-dimensional topological lattice by introducing spin orbit coupling of photons, creating a new method for topological quantum simulation. The research results were published in the internationally renowned academic journal Nature Communications on April 19.

Dimension is an important physical quantity that determines the properties of matter in the universe. However, in scientific research, due to the limitations of the three-dimensional physical world, it is often difficult to study the properties and evolutionary characteristics of physical systems above three dimensions. In order to solve this problem, the researchers proposed that it can be solved by artificial synthesis of dimensions. For example, by introducing two synthetic dimensions into a three-dimensional system, it is possible to study the physical properties of five dimensions on that system.

Schematic diagram of experimental setup and theoretical model: a. Degenerate optical resonator b. Synthetic photonic orbital angular momentum lattice

The amount of orbital angular momentum carried by vortex photons can be infinite in principle, which is an ideal carrier for constructing synthetic dimensions. As early as 2015, Professor Zhou Zhengwei's research team of the Key Laboratory of Quantum Information of the Chinese Academy of Sciences first theoretically proposed a quantum simulation scheme based on the orbital angular momentum dimension of artificially synthesized photons. Li Chuanfeng, Xu Jinshi et al. have carried out long-term experimental exploration in this direction, and built degenerate optical cavities based on plane, spherical and elliptic mirrors [Opt.Lett. 42, 2042 (2017); Appl. Phys. Lett. 112, 201104 (2018); Opt.Lett. 44, 5254 (2019)], to achieve resonance of orbital angular momentum modes of more than 46 orders in the cavity. On this basis, the research team creatively introduced an anisotropic liquid crystal phase plate (as shown in Figure a) into the standing wave degenericity cavity to realize the coupling of the orbital angular momentum of the vortex photon and the photon spin (i.e., polarization) in the cavity. The orbital angular momentum carried by the photon in the cavity is integer discrete, corresponding to the one-dimensional discrete lattice. Therefore, photons carrying different orbital angular momenta can be equivalent to quasticles located on different lattice points, and photons with different orbital angular momenta are coupled through spin degrees of freedom, so as to simulate the back and forth transition of particles between different lattice points (as shown in Figure b). The state density and band structure of the spin-orbit coupled system were directly described by using resonance energy spectrum detection. Using the excellent tunable performance of the experimental device, the team clearly demonstrated the evolution of the band opening and closing of the periodic drive system. The research group further introduced different evolutionary time series, systematically studied the characteristics of different topological structures and detected the topological winding number.

This result verifies the feasibility of using the intrinsic spin and orbital angular momentum of vortex photons as synthetic dimensions, and provides a highly compact experimental platform for the study of rich topological physical systems.

The co-first authors of the paper are Yang Mu, a doctoral candidate at the Key Laboratory of Quantum Information of the Chinese Academy of Sciences, and Haoqing Zhang and Yuwei Liao, master's candidates. This research was supported by the Ministry of Science and Technology, the National Foundation Commission, the Chinese Academy of Sciences, and Anhui Province.

The thesis links: https://www.nature.com/articles/s41467-022-29779-3



(Key Laboratory of Quantum Information, Academy of Quantum Information and Quantum Technology Innovation, Scientific Research Department, Chinese Academy of Sciences)