Chiral switching of many-body steady states in a dissipative Rydberg gas.

Dissipative Rydberg gases are an outstanding platform for the investigation of many-body open systems. Despite the wealth of existing studies, the non-equilibrium dynamics of dissipative Rydberg gases has rarely been examined or harnessed through the lens of non-Hermitian physics, which is intrinsic to open systems. Here we report the experimental observation of chiral switching between many-body steady states in a dissipative thermal Rydberg vapor, which is underlain by an exceptional structure in the Liouvillian eigenspectrum of the system. Similar to typical chiral state transfer in non-Hermitian systems, as the parameters are adiabatically varied around a closed contour, depending on the chirality of the parameter modulation, the Rydberg vapor can change between two collective steady states with distinct Rydberg excitations and optical transmissions. Adopting a mean-field description, we reveal that both the existence of the bistable steady states and chiral dynamics derive from the Liouvillian exceptional structure, where two exceptional lines merge at a higher-order exceptional point. Such a non-Hermitian perspective of the dissipative Rydberg gas not only provides a new paradigm for chiral mode switching through many-body parameters, as we demonstrate experimentally, but also paves the way for devising novel applications based on the unique features of non-Hermitian physics.