In a study published in Nature Communications, a team led by Prof. GUO Guangcan, Prof. SHI Baosen and Prof. DING Dongsheng from the University of Science and Technology of China (USTC) of the Chinese Academy of Sciences observed multi-body interaction-induced exceptional points (EPs) and hysteresis trajectories in cold Rydberg atomic gases, and revealed the phenomenon of charge-conjugation parity (CP) symmetry breaking in non-Hermitian multi-body physics.

The CP-symmetry is a discrete symmetry in particle physics. When certain physical processes exhibit asymmetry under CP transformation, it is referred to as the breaking of CP-symmetry. Studying charge-parity symmetry breaking is beneficial for understanding the mechanism of matter-antimatter asymmetry in nature, as well as discovering sources of charge-parity breaking beyond what is predicted by the Standard Model.

Rydberg atoms provide an ideal platform for simulating and studying symmetry breaking phenomena in quantum many-body systems. Notably, the long-range interactions between Rydberg atoms can induce additional quantum dissipation channels, which makes it possible to build controllable multi-body non-Hermitian quantum systems experimentally, opening a new path for studying EPs and the related non-equilibrium dynamical behaviors.

In this study, researchers constructed a non-Hermitian model using multi-body interactions in the cold Rydberg atomic system. They observed second-order EPs induced by multi-body interactions between Rydberg atoms by experimentally measuring the atomic response under different probe light intensities. Theoretical analysis indicated that the Hamiltonian of the system possesses CP-symmetry, and this symmetry was broken at the EPs.

In addition, researchers revealed the existence of the third-order EPs in the system which showed important application prospects in the field of precision measurement. In such a system, the state of the Rydberg atoms was not only affected by the external input, but also restricted by their former state. 

Thus, the dynamical evolution of the system was completely different for scanning directions with laser power being either increased or decreased, and a hysteresis loop was created. The effect of scanning time on hysteresis for different atomic densities was studied, and the non-Hermitian response characteristics at different time scales were revealed.

This work builds a bridge between non-Hermitian multi-quantum physics and the CP problem in particle physics, providing new insights into the origin of cosmic matter, the limitations of the Standard Model, and the exploration of new physics.