Engineering and understand atomic topological matter with non-Hermiticity

Non-Hermitian concept has generalized the notion of band topology with associated exceptional points (EPs), also known as the parity-time symmetry breaking points, leading to various counter-intuitive phenomena. Non-Hermitian skin effect, involving the accumulation of eigenstates at the boundary, is one such circumstance, but its realization in a high dimensional quantum system remains unexplored. In this talk, we report the realization of a two-dimensional (2D) non-Hermitian topological band with ultracold fermions by combining spin-orbit-coupled optical lattices with tunable dissipation. A pair of EPs are created in the band structure, connected to each other by an open-ended bulk Fermi arc, in contrast to the contours with closed loops in Hermitian systems. The associated EPs emerge and shift with increasing dissipation, leading to the formation of Fermi arc. In this platform, we measure non-trivial spectral topology in the complex energy plane indicating the existence of 2D skin effect. This new platform provides a wide range of opportunities to study how non-Hermitian physics interplay with topology, symmetry, and other degrees of freedom in the quantum regime.