Enhancement of Kerr nonlinearity with vanishing absorption in a tripod scheme

The giant enhancement of Kerr nonlinearity in a four-level tripod type system is investigated theoretically. By tuning the value of the Rabi frequency of the coherent control field, owing to the double dark resonances, the giant-enhanced Kerr nonlinearity can be achieved within the right transparency window. The influence of Doppler broadening is also discussed.     

利用暗态共振之间的相互作用提高Kerr非线性

分析了利用双暗态共振之间的相互作用提高Kerr 非线性的方案,采用微扰理论和密度矩阵方法导出三阶极化率实部随外加相干驱动场失谐量变化的关系.结果表明,随着相干驱动场失谐量的增加,双暗态共振之间干涉使得Kerr非线性的最大值也随之变大且逐渐进入电磁感应透明窗口,并使用缀饰态理论对其产生的机制给予相应的解释.证明了在具有双暗态共振的四能级原子系统中获得无吸收巨Kerr非线性实现的可行性.     

Enhancement of Kerr nonlinearity and its application to entangled state discrimination

In this paper, the recent research on the enhanced Kerr nonlinearity and its application in entangled state discrimination is reported. Two kinds of dynamics, including interacting double dark resonances and spontaneously generated coherence, are presented to enhance the Kerr nonlinearity. The application of Kerr nonlinearity in quantum state discrimination is also discussed. An arbitrary Greenberger-Horne-Zeilinger state can be discriminated using two-photon polarization parity detection which resorts to cross-Kerr nonlinearity between a single-photon qubit and probe field. In addition, a scheme for Greenberger-Horne-Zeilinger state discrimination of matter qubits is also proposed using the dipole induced transparency in a cavity-dipole system.      

Coherent control of Kerr nonlinearity via double dark resonances

A theoretical scheme for enhanced Kerr nonlinearity is proposed in a four-level ladder-type atomic system based on double dark resonances (DDRs). We solve the relevant density matrix equations in steady state and utilize the perturbation theory to obtain the analytical expressions for the third order susceptibility of the atomic system. The influence of system parameters on behavior of the first and third order susceptibilities is then discussed. In particular, it is found that an enhanced Kerr nonlinearity with reduced linear and nonlinear absorption is obtained around zero probe detuning under the slow light condition through proper adjusting the laser field intensity and frequency detuning of driving fields. The dressed state analysis is employed to explain the physical origin of the obtained result. The obtained results may be important for all-optical signal processing and quantum information technology.     

Giant Enhancement and Sign Inversion of Optical Kerr Nonlinearity in Random High Index Nanocomposites near Mie Resonances

High-index dielectric nanoantennas excited at Mie-type resonances have exhibited enormous enhancement of optical nonlinearity. Such nanostructures have been actively studied by researchers in recent years. Here, a numerical analysis study of the optical Kerr effect of nanocomposites consisting of high refractive index (GaP) spheres at the wavelength of 532 nm is presented. This is done by means of 3D finite-difference time-domain simulations. The effective nonlinear refractive index of 0.8 µm thick nanocomposites and metasurfaces is evaluated. It is shown that the optical Kerr nonlinearity of the nanocomposites rises by orders in proximity to Mie resonances and may exceed the second-order refractive index of the bulk material. It is revealed that the sign of the effective optical Kerr coefficient is inverted near the Mie resonances. This effect may be of interest in developing nonlinear optical metadevices.     

Controllable Kerr nonlinearity with vanishing absorption in a four-level inverted-Y atomic system

The giant enhancement of Kerr nonlinearity in a four-level inverted-Y atomic system is investigated theoretically. Compared with that generated in a generic three-level system, the Kerr nonlinearity can be enhanced by several orders of magnitude with vanishing linear absorption. The physical mechanism leading to the giant enhancement of Kerr nonlinearity is also discussed.     

Effect of spontaneously generated coherence on Kerr nonlinearity in a four-level atomic system

We propose a scheme for giant enhancement of the Kerr nonlinearity in a four-level atomic system in which spontaneously generated coherence is present. The physics mechanism of the enhancement of Kerr nonlinearity is mainly based on the presence of an extra atomic coherence induced by the spontaneously generated coherence. Numerical values obtained by solving the density matrix equations agree well with these exact analytical values.     

Controllable Kerr Nonlinearity with Perfect Transparency in the Existence of Spontaneously Generated Coherence

We investigate the Kerr nonlinearity of a V-type three-level atomic system where the upper two states decay outside to another state and hence spontaneous generated coherence may exist. It is shown that dark state and hence perfect transparency present under certain conditions. Meanwhile, the Kerr nonlinearity can be controlled by manipulation of the decay rates and the splitting of the two excited states. Therefore, enhanced Kerr nonlinearity without absorption can be obtained under proper parameters.     

Giant Kerr nonlinearity induced by interacting quantum coherences from decays and incoherent pumping

A scheme for generating the giant enhancement of the Kerr nonlinearity in a four-level system with the quantum coherences from the decays and the incoherent pumping is proposed.Compared with that generated in a general fourlevel system,the Kerr nonlinearity can be enhanced by several orders of magnitude with vanishing linear absorption.By using the numerical results,we show that the remarkable enhancement should be attributed to the interaction of the quantum coherences from the decays and the incoherent pumping.     

Enhancement of Kerr nonlinearity via spontaneously generated coherence in a four-level N-type atomic system

A theoretical investigation is carried out into the effect of spontaneously generated coherence (SGC) on Kerr nonlinearity of a four-level N-type system. It’s found that the Kerr nonlinearity can be obviously enhanced with SGC present. We attribute the enhancement of Kerr nonlinearity mainly to the generation of extra coherences induced by the superposition of the two SGC channels, and when the superposition is controlled by the interference between two SGC channels properly, the maximal Kerr nonlinearity does not only enter the electromagnetically induced transparency window as the spontaneous generated coherences intensify, but also gets enhanced about 10 times with very large SGC coefficients than that with no SGC effect.     

Giant Kerr nonlinearity in an n-doped semiconductor quantum well

A scheme for enhancement of Kerr nonlinearity with vanishing linear and nonlinear absorption in a three-level ladder-configuration n-doped semiconductor quantum well is proposed. It is shown that the Kerr nonlinearity can be controlled and even enhance by the intensity of coupling fields. Also, phase control of Kerr nonlinearity is then discussed.     

Enhancement of Kerr nonlinearity at long wavelength in a quantum dot nanostructure

The giant Kerr nonlinearity with reduced linear and nonlinear absorption in a four-level quantum dot by employing the tunnel coupling is investigated. It is shown that by enhancement of tunnel coupling value the Kerr nonlinearity increases and at the same time linear and nonlinear absorption reduces at the long wavelength which is very important for communicational applications. Enhanced of Kerr nonlinearity in a double quantum dots is investigated. It is found that the electron tunneling has an essential role to reducing the linear absorption and increasing the Kerr nonlinearity at long wavelength.     

Enhancing Kerr nonlinearity via quantum interference from incoherent pumping

The effect of quantum interference from incoherent pump field on the Kerr nonlinearity of V- and Lambda-type three-level systems is investigated. It is found that enhanced Kerr nonlinearity can be obtained via quantum interference of incoherent pump field. It is also demonstrated that the enhanced Kerr nonlinearity is located in the reduced-absorption region. The enhancement of Kerr nonlinearity is attributed mainly to the presence of extra atomic coherence induced by quantum interference from incoherent pump field.     

Control of Group Velocity via Spontaneous Generated Coherence and Kerr Nonlinearity

A four-level N-type atomic medium is considered to study the effect of spontaneous generated coherence(SGC) and Kerr nonlinearity on light pulse propagation. A light pulse is propagating inside the medium where each atom follows four-level N-type atom-field configuration of rubidium(85Rb) atom. The atom-field interaction leads to electromagnetically induced transparency(EIT) process. The atom-field interaction is accompanied by normal dispersion and in the presence of SGC and Kerr nonlinearity the dispersion property of the proposed atomic medium is modified,which leads to enhancement of positive group index of the medium. The enhancement of positive group index then leads to slow group velocity inside the medium. A more slow group velocity is also investigated by incorporated the collective effect of SGC and Kerr nonlinearity. The control of group velocity inside a four-level N-type atomic medium via collective effect of SGC and Kerr nonlinearity is the major part of this work.     

Control of Group Velocity via Spontaneous Generated Coherence and Kerr Nonlinearity

A four-level N-type atomic medium is considered to study the effect of spontaneous generated coherence (SGC) and Kerr nonlinearity on light pulse propagation. A light pulse is propagating inside the medium where each atom follows four-level N-type atom-field configuration of rubidium (⁸⁵Rb) atom. The atom-field interaction leads to electromagnetically induced transparency (EIT) process. The atom-field interaction is accompanied by normal dispersion and in the presence of SGC and Kerr nonlinearity the dispersion property of the proposed atomic medium is modified, which leads to enhancement of positive group index of the medium. The enhancement of positive group index then leads to slow group velocity inside the medium. A more slow group velocity is also investigated by incorporated the collective effect of SGC and Kerr nonlinearity. The control of group velocity inside a four-level N-type atomic medium via collective effect of SGC and Kerr nonlinearity is the major part of this work.     

Enhancement of nonlinear susceptibilities near plasmonic metamaterials

It is shown that the Kerr nonlinearity of a two-level atom placed in the vicinity of a two-dimensional array of metal-coated silica nanoparticles can be greatly enhanced due to quenching of both radiative and non-radiative spontaneous-emission paths for frequencies near the surface plasmon resonances. The spontaneous emission rate is calculated by rigorous electrodynamic calculations of the electric-field Green’s tensor. The Kerr susceptibility can be enhanced by two orders of magnitude even for large detunings heralding, this way, the observation of nonlinear phenomena for moderate radiation intensities.     

Thirring optical solitons with Kerr law nonlinearity

The dynamics of Thirring solitons in birefringent fibers with Kerr law nonlinearity is addressed in this paper. An exact 1-soliton solution is obtained. Bright, dark and singular soliton solutions are described.     

Kerr nonlinearity and EIT in a double Lambda type atomic system

The giant Kerr nonlinearity in a four-level double Lambda type atomic system is theoretically predicted. We find that an enhanced Kerr nonlinearity can be achieved just by the intensity of coupling filed that lies within the transparency window. It is also shown that the giant Kerr nonlinearity with reduced absorption can be achieved by the quantum interference mechanisms.     

Observation of large Kerr nonlinearity at low light intensities

We report an experimental observation of large Kerr nonlinearity with vanishing linear susceptibilities in coherently prepared four-level rubidium atoms. Quantum coherence and interference manifested by electromagnetically induced transparency suppress the linear susceptibilities and greatly enhance the nonlinear susceptibilities at low light intensities. The measured Kerr nonlinearity is comparable in magnitude to the linear dispersion in a simple two-level system and is several orders of magnitude greater than the Kerr nonlinearity of a conventional three-level scheme under similar conditions.     

All optical switch based on Fano resonance in metal nanocomposite photonic crystals

We investigate the potential of plasmonic resonance in metal nanocomposite materials for the design of photonic crystal all optical switches by numerical methods. We study the absorption effect of the plasmonic resonance on the Fano resonances of one dimensional photonic crystal slabs covered by a metal nanocomposite layer. It is shown that the absorption reduces the contrast of the Fano resonances. However, for adequate metal nanoparticle concentrations it is possible to achieve both sufficiently sharp Fano resonance and strong Kerr nonlinearity, which provides a suitable condition for the design of high contrast and low threshold switches.