There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality.

Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

I and i

Optical vortices exhibit a corkscrew-like shape as they travel. The study of this phenomenon, known as singular optics, is now extended to the high-power regime where high-harmonic processes become evident. This type of radiation could help illuminate novel attosecond phenomena in atoms and molecules.

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Strong-field physics with singular light beams

Beams of ``squeezed'' light have important applications in quantum metrology and gravitational-wave detection. The authors generate twin beams of correlated photons using parametrically amplified four- and six-wave mixing in a nonlinear optical crystal. This medium offers several advantages, such as better on-chip integration than atomic vapors, plus a longer coherence time than traditional optical materials. These achievements can also find potential application in all-optical communication and quantum storage of light in photonic circuits.

Controlled Correlation and Squeezing in Pr 3 + : Y 2 SiO 5 to Yield Correlated Light Beams

The self-Kerr-nonlinearity of a four-level N-type atomic system is studied both experimentally and theoretically. The self-Kerr-nonlinear coefficient n{sub 2} of the probe beam is greatly enhanced near atomic resonance, and can be dramatically modified by changing the switching laser power. With an increasing switching laser power, the slope of the Kerr nonlinear coefficient n{sub 2} around the atomic resonance changes from negative to positive, and the value of n{sub 2} varies from {approx}-4 x 10{sup -6} to 4 x 10{sup -6} cm{sup 2}/W at certain near-resonant probe frequency detunings. Such controllable Kerr nonlinearity can find applications in optoelectronic devices, such as all-optical switching and logic gates.

Modified self-Kerr-nonlinearity in a four-level N-type atomic system

We propose that a coherently prepared four-level atomic medium can provide a versatile platform for realizing parity-time ($\mathcal{PT}$) symmetric optical potentials. Different types of $\mathcal{PT}$-symmetric potentials are proposed by appropriately tuning the exciting optical fields and the pertinent atomic parameters. Such reconfigurable and controllable systems may open up new avenues in observing $\mathcal{PT}$-related phenomena with appreciable gain-loss contrast in coherent atomic media.

PT-symmetric optical potentials in a coherent atomic medium

We demonstrate a novel type of stable multicomponent vector solitons consisting of two perpendicular four-wave mixing (FWM) dipole components induced by electromagnetically induced gratings. We analyze the formation and steering of the steady dipole solitons and their dynamical (energy transfer) effects. The dipole-mode solitons of two FWM processes have horizontal and vertical orientations, respectively. Omnidirectional Bragg reflections are also investigated.

Four-Wave Mixing Dipole Soliton in Laser-Induced Atomic Gratings

We study three (nested, parallel, and sequential cascade) types of schemes for doubly dressed four-wave-mixing processes in an open five-level atomic system. The interaction between two dressing fields of the nested-cascade scheme is strongest and weakest for the parallel-cascade scheme, with the sequential scheme intermediate between them. Mutual-dressing processes and constructive or destructive interference between two coexisting dressed multiwave mixing channels in such a system are also considered. Investigations of these multidressing mechanisms and interactions are very useful to understand and control the generated high-order nonlinear optical signals.

Interacting multiwave mixing in a five-level atomic system

We demonstrate Autler–Townes (AT) splitting of four-wave mixing in an electromagnetically induced transparency window, which results from the destructive interference between a three-photon process and a five-photon process. The primary and secondary AT splittings are achieved via induced atomic coherence in a four-level Y-type atomic system. Theoretical calculations fit well with the experimentally measured results. Such controlled multichannel splitting of nonlinear optical signals can have potential applications in optical communication and quantum information processing.

Evidence of Autler–Townes splitting in high-order nonlinear processes

We theoretically investigate the dually dressed electromagnetically induced transparency, and the multidressed four-wave mixing (FWM) and six-wave mixing (SWM) processes in an inverted-$Y$-type atomic system with Zeeman sublevels. The results show that the Zeeman degeneracy of the dark states can be lifted by the dressing field as its intensity is increased. Moreover, the derived analytical expressions indicate that one can, for example, selectively create secondary dark states on the multi-Zeeman-sublevel dark states (by tuning the coupling field), distinguish two different types of dark states generated in two FWM processes (by properly controlling the coupling field intensity), and selectively enhance multi-FWM signals coming from various paths consisting of split Zeeman sublevels (by tuning the dressing field). The SWM signals can be either enhanced or suppressed by controlling the dressing field.

Controlling four-wave mixing and six-wave mixing in a multi-Zeeman-sublevel atomic system with electromagnetically induced transparency

We report our observations of enhancement and suppression between two competing four-wave mixing (FWM) processes. The results show the evolution of the dressed effects (from pure enhancement into pure suppression) in the degenerate FWM processes. Moreover, due to induced atomic coherence in the system, there exist different interplays between these two FWM processes via different detuning parameters. In addition, the power dependences of enhancement and suppression are studied. Theoretical calculations are carried out, which are in good agreement with the experimental observations.

Zhiqiang Nie

Papers

Four-Wave Mixing Dipole Soliton in Laser-Induced Atomic Gratings

Interacting multiwave mixing in a five-level atomic system

Evidence of Autler–Townes splitting in high-order nonlinear processes

Controlling four-wave mixing and six-wave mixing in a multi-Zeeman-sublevel atomic system with electromagnetically induced transparency

Observation of enhancement and suppression in four-wave mixing processes