Charge-parity symmetry breaking revealed in Rydberg atom multibody systems

A research team has observed multibody interaction-induced EPs and hysteresis trajectories in cold Rydberg atomic gases. They revealed the phenomenon of charge-conjugation parity (CP) symmetry breaking in non-Hermitian multibody physics.

The team was 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, and their study was published in Nature Communications.

CP-symmetry is an important discrete symmetry in particle physics. When certain physical processes exhibit asymmetry under CP transformation, it is referred to as the breaking of CP-symmetry, such as in the decay of neutral K mesons (K⁰) and B meson decay.

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, with their large electric dipole moments and excellent quantum coherence properties, 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 multibody non-Hermitian quantum systems experimentally, opening a new path for studying exceptional points (EPs) and related non-equilibrium dynamical behaviors.

Researchers constructed a non-Hermitian model using multibody interactions in the cold Rydberg atomic system, discovered the phenomenon of CP-symmetry breaking, and observed the hysteresis trajectories caused by non-Hermitianity.

Researchers have successfully observed second-order EPs induced by multibody 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, the theoretical analysis revealed the existence of the third-order EPs in the system. These higher-order EPs 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 work also studied the effect of scanning time on hysteresis for different atomic densities, revealing the non-Hermitian response characteristics at different time scales.

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.