Nonlinear topological laser on the non-Hermitian Haldane model with higher-order corner states.

The non-Hermitian skin effect (NHSE) on the non-Hermitian Haldane model with gain and loss on the honeycomb lattice with the outline of a triangle is discussed. The NHSE only occurs on the edge of the lattice, transforming the edge modes into the higher-order corner modes. The NHSE can also occur on a lattice with only loss, which can be treated as a lattice with gain and loss as well as a global loss added to it. When the saturated gain is added to the three corner sites of the dissipative lattice, a single-mode laser system is obtained. When any one site is stimulated initially, the system will reach a saturated state depending on the distribution of the corner modes, and the stable laser light is emitted by sites at the corners.

Influence of a topological artificial atom chain on the transmission properties of a cavity.

We explore the influence of the artificial atomic chain on the input-output relation of the cavity. Specifically, we extend the atom chain to the one-dimensional Su-Schrieffer-Heeger (SSH) chain to check the role of atomic topological non-trivial edge state on the transmission characteristics of the cavity. The superconducting circuits can realize the artificial atomic chain. Our results show that the atom chain is not equivalent to atom gas, and the transmission properties of the cavity containing the atom chain are entirely different from that of the cavity containing atom gas. When the atom chain is arranged in the form of topological non-trivial SSH model, the atom chain can be equivalent to the three-level atom, in which the edge state contributes to the second level and is resonant with the cavity, while the high-energy bulk state contributes to form the third level and is greatly detuned with the cavity. Therefore, the transmission spectrum shows no more than three peaks. This allows us to infer the topological phase of the atomic chain and the coupling strength between the atom and the cavity only from the profile of the transmission spectrum. Our work is helping to understand the role of topology in quantum optics.

Topological laser with higher-order corner states in the 2-dimensional Su-Schrieffer-Heeger model.

A nonlinear non-Hermitian topological laser system based on the higher-order corner states of the 2-dimensional (2D) Su-Schrieffer-Heeger (SSH) model is investigated. The topological property of this nonlinear non-Hermitian system described by the quench dynamics is in accordance with that of a normal 2D SSH model. In the topological phase, all sites belonging to the topological corner states begin to emit stable laser light when a pulse is given to any one site of the lattice, while no laser light is emitted when the lattice is in the trivial phase. Furthermore, the next-nearest-neighbor (NNN) couplings are introduced into the strong-coupling unit cells of the 2D SSH model, which open a band gap in the continuous band structure. In the topological phase, similar to the case of 2D SSH model without NNN couplings, the corner sites can emit stable laser light due to the robustness of the higher-order corner states when the NNN couplings are regarded as the perturbation. However, amplitude of the stimulated site does not decay to zero in the trivial phase, because the existence of the NNN couplings in the strong-coupling unit cells make the lattice like one in the tetramer limit, and a weaker laser light is emitted by each corner.

Nonclassical correlations of photonic qubits carrying orbital angular momentum through non-Kolmogorov atmospheric turbulence.

We consider the non-horizontal distributions of orbital angular momentum biphotons through free-space atmospheric channels, in which case the non-Kolmogorov turbulent effects shall be considered. By considering the case of initial non-perfect resource, i.e., the orbital angular momentum biphotons are initially prepared in an extended Werner-like state, we investigate the non-Kolmogorov effects on the propagations of nonclassical correlations, including quantum entanglement and quantum discord. It is found that universal decay laws of entanglement and discord also exist for non-Kolmogorov turbulence but with their decay curves different from that of entanglement for Kolmogorov turbulence reported by Leonhard et al. [Phys. Rev. A91, 012345 (2015)PLRAAN1050-294710.1103/PhysRevA.91.012345]. We show that the universal decay laws are dependent on the power-law exponent of the non-Kolmogorov spectrum and compare the differences of decay properties between entanglement and discord caused by non-Kolmogorov turbulence.