Probing non-Hermitian physics with flying atoms

Jianming Wen, Yanhong Xiao, Peng Peng +4 more

J. F. Chen

The flying photons are stored into an atomic cloud as “magnons”, i.e., the ground-state atomic excitation. A tunable magnon-photon beam-splitter, which induces interference from Hermitian to non-Hermitian, is demonstrated through a cold atomic cloud.

Masahito Ueda

Ygor Pará, Giandomenico Palumbo, Tommaso Macrì

Non-Hermitian Hamiltonians are relevant to describe the features of a broad class of physical phenomena, ranging from photonics and atomic and molecular systems to nuclear physics and mesoscopic electronic systems. An important question relies on the understanding of the influence of a curved background on the static and dynamical properties of non-Hermitian systems. In this work, we study the interplay of geometry and non-Hermitian dynamics by unveiling the existence of curvature-dependent non-Hermitian phase transitions. We investigate a prototypical model of Dirac fermions on a sphere with an imaginary mass term. This exactly solvable model admits an infinite set of curvature-dependent pseudo-Landau levels. We characterize these phases by computing an order parameter given by the pseudomagnetization and, independently, the non-Hermitian fidelity susceptibility. Finally, we probe the non-Hermitian phase transitions by computing the (generalized) Loschmidt echo and the dynamical fidelity after a quantum quench of the imaginary mass and find singularities corresponding to exceptional radii of the sphere.

Xingchang Wang, Jianmin Wang, Georgios A. Siviloglou +1 more

We report an atom-light beamsplitter-type interface, in which flying photons and stored atomic coherence can be transformed reversibly. The degree of Hermiticity of this interface can alter the atom-photon quantum interference from bosonic to fermion-like.

Yuntao Xiao, Yuchen Guo, Xiaojian Huang +6 more

Non-Hermitian systems host phenomena absent in Hermitian physics, but realizing Hamiltonians with intrinsic non-Hermitian properties remains challenging. The theoretical method of non-Hermitian parent Hamiltonian (NH-PH) enables the construction of a non-Hermitian system from a pair of matrix product states (MPSs) with tailored properties. Here, we report the first experimental generation of NH-PHs. This generation starts from MPSs that represent asymmetric Affleck--Kennedy--Lieb--Tasaki (AKLT) states. The construction is validated with single photons via imaginary-time evolution of the generated NH-PH to obtain its left and right ground states. We then characterize the properties of the system by measuring four different order parameters that probe non-reciprocal correlations, chiral imbalance, and conventional antiferromagnetic correlations. Furthermore, extending the framework to a larger system with a different model, we observe an intrinsic non-Hermitian phase transition, manifested by abrupt jumps of an order parameter when the designated zero-energy modes cease to be the globally lowest-energy states. Our work provides the first experimental realization and characterization of non-Hermitian Hamiltonians with controllable and customizable properties, opening new avenues for exploring intrinsic non-Hermitian phenomena across diverse physical platforms.