Hui-jun Li

PT symmetry via electromagnetically induced transparency

We propose a scheme to realize parity-time (PT) symmetry via electromagnetically induced transparency (EIT). The system we consider is an ensemble of cold four-level atoms with an EIT core. We show that the cross-phase modulation contributed by an assisted field, the optical lattice potential provided by a far-detuned laser field, and the optical gain resulted from an incoherent pumping can be used to construct a PT-symmetric complex optical potential for probe field propagation in a controllable way. Comparing with previous study, the present scheme uses only a single atomic species and hence is easy for the physical realization of PT-symmetric Hamiltonian via atomic coherence.

Surface solitons in nonlinear lattices

We investigate the existence of spatial optical solitons supported by an interface between two nonlinear lattices with different saturation parameters. Dipole, quadrupole, and vortex solitons are found in the nonlinear surface lattices. The slight different saturation degree between two sides of the interface leads to a remarkable asymmetry of solitons with higher power. We reveal that multipole and vortex solitons are stable when their power exceeds a threshold value, and stable localized surface nonlinear modes with very high peaks are possible.

Storage and retrieval of (3 + 1)-dimensional weak-light bullets and vortices in a coherent atomic gas

A robust light storage and retrieval (LSR) in high dimensions is highly desirable for light and quantum information processing. However, most schemes on LSR realized up to now encounter problems due to not only dissipation, but also dispersion and diffraction, which make LSR with a very low fidelity. Here we propose a scheme to achieve a robust storage and retrieval of weak nonlinear high-dimensional light pulses in a coherent atomic gas via electromagnetically induced transparency. We show that it is available to produce stable (3 + 1)-dimensional light bullets and vortices, which have very attractive physical property and are suitable to obtain a robust LSR in high dimensions.

Stable weak-light ultraslow spatiotemporal solitons via atomic coherence

We propose a scheme to generate stable ultraslow three-dimensional spatiotemporal optical solitons, or ultraslow optical bullets, at very low light levels via atomic coherence. The system we consider is an ensemble of resonant, lifetime-broadened N-type four-level atoms, working in a regime of electromagnetically induced transparency. Due to the quantum interference effect induced by a control field, the absorption of a probe field is largely suppressed. Moreover, the Kerr nonlinearity is greatly enhanced, and the dispersion property of the probe field is drastically changed. Using a method of multiple scales, we derive two coupled nonlinear envelope equations controlling the evolution of the envelopes of the probe field and an assisted field. We show that under certainconditionstheenvelopeoftheprobefieldsatisfiesathree-dimensionalnonlinearSchr¨ odingerequationand the envelope of the assisted field obeys a linear Helmholtz equation. We obtain various optical bullet solutions for the probe-field envelope and demonstrate that such optical bullets have many novel features, including very slow propagating velocity and very low generation power. In addition, they can be actively controlled and manipulated by adjusting system parameters. The stabilization of the optical bullets obtained can be easily realized by the trapping potential contributed by the assisted field, which is also investigated in detail.

Depletion of control field during the propagation of ultraslow optical solitons

We study nonlinear excitations in a lifetime-broadened Λ-type three-level atomic system with a configuration of electromagnetically induced transparency. Different from previous works, we show that a significant depletion of the control field may occur during the formation and propagation of ultraslow optical solitons for the probe field. We demonstrate that ultraslow optical solitons predicted in previous works correspond to the limits of weak dispersion and weak nonlinearity, adiabatons correspond to the limits of stronger dispersion and stronger nonlinearity, and simultons correspond to the limits of strong dispersion and strong nonlinearity. Between these different limits the system also yields solitonlike nonlinear excitations with different levels of depletion of the control field. The results provided here are useful not only for a deep understanding of the interrelation between ultraslow optical solitons, adiabatons, and simultons, but also for potential applications in optical information processing and transmission.