Observation of exceptional points and skin effect in a 2D non-Hermitian topological band

The open quantum system, which can be effectively described by a non-Hermitian Hamiltonian, often shows a spectral singularity known as exceptional points. Recently, the concept of non-Hermitian has also been generalized to the lattice system in which the exceptional points are created in the band structure in momentum space and many intriguing phenomena have been theoretically explored. In this talk, we report the realization of a 2D non-Hermitian topological band in an optical Raman lattice with tunable dissipation for ultracold fermions. Within this platform, we observe the emergence and shift of the exceptional points in our 2D topological band when the spin-dependent dissipation increases. With momentum-dependent Rabi spectroscopy, the band gap information can be reconstructed from the time evolution of spin texture. The reconstructed spectral topology in the complex energy plane further indicates the existence of skin effect in our optical Raman lattice system. It is expected that this platform would allow us to further expand the possibilities to explore the unique phenomena in non-Hermitian lattice systems.