Electromagnetically induced quantum memory

We discuss the problem of creating coherence in an optically driven quantum system in conditions where decoherence is caused by the laser field itself, due to coupling of the system to a rapidly decaying state or continuum. It is shown that by applying an additional laser field between this state and a bound state the relaxation channel can be suppressed as a result of a "dark state" formation, giving rise to long living Rabi oscillations in the system. It is found that the same mechanism of preserving coherence exists in systems with level splitting or degeneracy, where the driving field interacts with multiple resonant sublevels simultaneously. We also show that specific coherent propagation phenomena assisted by the interference suppression of decoherence can be observed under these conditions.     

Investigation of atomic coherence in multilevel systems with embedded tunable dark state superposition

The coherent superposition of two-atomic levels induced by coherent population trapping is employed in the two-level system, the standard three-level Λ type scheme and the four-level N-type systems and a weak probe pulse scans across the system. A theoretical analysis about the response of medium to the probe field is given. It is shown that under different initial conditions, the coherent superposition of the dark state exhibits abundant optical phenomena response to the probe field. It can change the absorption or gain and the dispersion relationship in the medium experienced by the probe. In the embedded three-level scheme, the probe experiences a crossover from absorption to transparent and then to amplification. Consequently the group velocity of the probe pulse can be controlled to propagate either as a subluminal, a standard, a superluminal or even a negative speed. In the embedded four-level N-type system, it can give an enhancement to the Giant Kerr effect and overcome the limitation of two-photon absorption, then make the nonlinear properties of the medium richer than the traditional N-type scheme.     

Formation of nonclassical states of light in media with a three-photon resonance

The process of simultaneous absorption of three photons in a medium subjected to a three-photon parametric perturbation is considered. It is shown that in such a medium one can observe the formation of the radiation field states, which are the quantum superposition of three coherent components. One-photon and twophoton absorption processes in the medium also destroy the interference between the components of the superposition state. The states being formed are investigated in both the temporal development (numerically) and the stationary limit (numerically and analytically); the Wigner functions, as well as the quantum entropy, are calculated for a whole series of initial states. It is shown that depending on the initial state of the radiation field, the interference between the three-component superposition states being formed can lead, for example, to the almost total localization of the system in a two-component state or to the destruction of the interference between different coherent components.     

半导体中光的相干传播理论(Ⅲ)

本文是半导体中光的相干传播理论的第三部分。在前面两篇文章的基础上,推导了光在半导体中相干传播的Maxwell-Bloch方程;利用这组方程,讨论了带间跃迁和激子跃迁两种情况的许多可能的相干传播效应。文中特别着重分析了自感透明现象,证明了对于上述两种跃迁自感透明现象都是可能发生的。 关键词：     

Propagation and coherence properties of higher order partially coherent dark hollow beams in turbulence

We formulate and evaluate in terms of graphical outputs, source and receiver plane expressions, the complex degree of coherence, beam size variation and power in bucket performance for higher order partially coherent dark hollow beams propagating in turbulent atmosphere. Our formulation is able to cover square, rectangular, circular, elliptical geometries for dark hollow and flat-topped beams in one single expression. From the graphical outputs of the receiver plane, it is observed that higher order partially coherent dark hollow beams will initially develop an outer ring around a central lobe, but will eventually evolve towards a Gaussian shape as the propagation distance is extended. It is further observed that stronger turbulence levels and greater partial coherence have similar effects on beam profile. During propagation, modulus of complex degree of coherence of partially coherent dark hollow beams appears to rise above that of the source plane values, reaching as high as near unity. Beam size analysis shows that, among the types examined, (nearly) flat-topped beam experiences the least beam expansion. Power in bucket analysis indicates that lowest order square fully coherent dark beam offers the best power capturing.     

Nonparaxial propagation of a partially coherent dark hollow beam

Based on the generalized Raleigh-Sommerfeld diffraction integral, an analytical nonparaxial propagation formula of a partially coherent dark hollow beam (DHB) in free space is derived. The paraxial approximation is dealt with as a special case of our general result. By using the derived formula, the nonparaxial propagation properties of DHBs are studied and are compared with the paraxial results. It is shown that the nonparaxiality properties of a partially coherent DHB are closely related to its initial beam parameters (i.e., beam waist size, wavelength, coherence length, dark size) and the propagation distance.     

Generation of pulses upon nonresonant acousto-electromagnetic interaction

New mechanisms of generation of acoustic and electromagnetic soliton-like pulses in an optoelastic medium upon nonlinear nonresonant interaction of the polarization components of an electromagnetic field with acoustic oscillations in the medium are considered. It is shown that the acousto-electromagnetic interaction in such a system may lead to the formation of coherent soliton excitations in a thin crystal plate. It is found that a modulation instability occurs in an extended medium, which is caused by the spatial effects and leads to the generation of transverse sound waves. The evolution of a light field in a one-dimensional extended periodic optoelastic medium is also considered. It is shown that acoustic and electromagnetic solitons can be generated due to the mixing of direct and backward optical waves and their nonresonant interaction with a sound wave.     

原子相干对里德伯原子稳定性的影响

研究了含级联双光子过程的多束缚态激光场诱导原子连续态结构系统中原子的相干捕获,给出了产生相干捕获的条件及暗态的表达式,讨论了原子初态和激光强度对原子相干捕获及粒子布居值在束缚态上分布的影响,揭示了原子相干对稳定里德伯原子的重要作用。     

Optimal beams for propagation through random media

The problem of maximizing the intensity that is transferred from a transmitter aperture to a receiver aperture is considered in which the propagation medium is random. Two optimization criteria are considered: maximal expected intensity transfer and minimal scintillation index. The beam that maximizes the expected intensity is shown to be fully coherent. Its coherent mode is determined as the principal eigenfunction for a kernel that is determined through the second-order moments of the propagation Green's function. The beam that minimizes the scintillation index is shown to be partially coherent in general, with its coherent modes determined by minimizing a quadratic form that has nonlinear dependence on the coherent-mode fields, and on the second- and fourth-order moments of the propagation Green's function.     

Subwavelength Hyperlens Resolution With Perfect Contrast Function

Recently it has been shown that plasmonic effects in hyperbolic metamaterials may facilitate overcoming the diffraction limit and enhance the contrast function of an image by filtering background radiation. Unfortunately, the contrast function of such a dark‐field hyperlens degrades in the deep‐subwavelength regime. We push forward the concept of the contrast function revival in the subwavelength imaging by introduction of the proper phase difference between coherent sources. To study this effect we develop a simplified theory of the wave propagation through a hyperbolic metamaterial and show that, in principle, two sources standing apart at any subwavelength distance can be distinguished. We suggest two feasible designs, the first of which employs the obliquely incident light, while the second one is based on a properly designed metasurface. The concept can be used in high‐contrast subwavelength microscopy.     

Quantum polarization fluctuations of partially coherent dark hollow beams in non-Kolmogorov turbulence atmosphere

Non-classical polarization properties of dark hollow beams propagating through non-Kolmogorov turbulence are studied. The analytic equation for the polarization degree of the quantization partially coherent dark hollow beams is obtained.It is found that the polarization fluctuations of the quantization partially coherent dark hollow beams are dependent on the turbulence factors and beam parameters with the detection photon numbers. Furthermore, an investigation of the changes in the on-axis propagation point and off-axis propagation point shows that the polarization degree of the quantization partially coherent dark hollow beams presents oscillation for a short propagation distance and gradually returns to zero for a sufficiently long distance.     

Kinetics of photoinduced optical anisotropy in oxide glass

Long-lived optical anisotropy generated in glasses by bichromatic mutually coherent radiation is associated with the accumulation of a built-in electric field. The kinetics of photoinduced anisotropy was studied within the framework of a phenomenological model taking into account the polarization-and current-induced mechanisms of field formation and the medium conductivity. The combination of the current and polarization mechanisms gives rise to new effects. The accumulation of anisotropy and its dark relaxation have a nonmonotonic character. For a sufficiently high and rapidly relaxing photoconductivity, “hidden writing” is possible, for which the anisotropy is absent during the course of bichromatic illumination, but it appears after switching off the light and relaxes slowly due to dark conduction.     

Coherent forward four-wave mixing of ultrashort radiation pulses in a resonant medium

Forward four-wave mixing (FFWM) of ultrashort light pulses is considered theoretically under their coherent propagation in a resonant-absorbing medium. Nonlinear equations describing FFWM are obtained and studied and it is shown that the energy exchange between pulses of exact resonance may lead to the enhancement of weak radiation. The influence of input radiation parameters and interaction geometry on the FFWM characteristics has been studied.     

Enhanced nonlinear generation in a three-level medium with spatially dependent coherence

We consider a method for efficient parametric generation of a laser pulse. A single laser field is injected into a three-level medium that has two lower states and one excited state. The lower states are initially prepared in a position-dependent coherent superposition state. It is shown that, by proper choice of the position dependence of the superposition along the direction of propagation, the incoming field can be completely converted to a new field.     

Special Property of Group Velocity for Temporal Dark Soliton

We investigate the speed of temporal dark soliton based on an optical coherent medium. It is demonstrated that the temporal dark soliton is described by a nonlinear Schrodinger equation whose coefficients are decided by the coherent medium. It is found that the speed of temporal dark soliton not only relies on the linear responses including GV parameter, group velocity dispersion parameter as well as the amplitude of dark soliton, but also relies on the nonlinear response like self-phase modulation parameter. Additionally, the dark soliton in anomalous-dispersion regime propagates slower than bright soliton, while in normal-dispersion regime it inversely propagates faster than bright soliton. The complicated property of the speed for dark soliton is quite different from the bright soliton whose speed is commonly only related to the group velocity parameter. We attribute this feature to the modulation instability of the nonlinear system.     

Role of incoherent pumping field on absorption–dispersion properties of probe pulse in a graphene nanostructure under external magnetic field

The optical properties of weak probe light based on quantum coherence and interference in Landau-quantized graphene nanostructure driven by two coherent fields and incoherent pumping field is investigated. The linear dynamical properties of the graphene by means of density matrix method and perturbation theory are discussed. It is found that under certain condition and for appropriate choosing the parameters of the medium, the absorption, dispersion, group index of the weak probe light can be controlled. Moreover, it is shown that by means of incoherent pumping field the superluminal light propagation in the system is accompanied by amplification to make sure that the probe field is amplified as it passes through the system. Moreover, it is observed that the probe amplification can be obtained in the presence or absence of population inversion by properly choosing of system’s parameters. We hope that these results may have useful in the future quantum communicational system and networks.     

Storage of quantum optical information based on the intracavity polaritons under the Bose-Einstein condensation condition

The propagation of optical wave packets in the atomic medium that is placed inside the cavity is considered under the conditions for the strong coupling of atoms and the quantized field. Primary attention is paid to the mechanisms for the formation of coherent polaritons determined by the bound state of the optical field and atomic medium at the lower branch of the dispersion curves of these states. Significant variations (slowing) in the group velocity of the optical wave packets under quasi-condensation (or true condensation) conditions of polaritons are analyzed. An algorithm for the spatially distributed quantum recording, storage, and readout of the information related to the wave packet propagation is proposed.     

非局域高次非线性介质中的多极暗孤子

研究一维非局域三-五次非线性模型下,暗孤子和多极暗孤子的新解和传输特性.发现非局域程度和非线性参量变化对暗孤子的峰值和束宽产生影响,并且在特定的竞争非局域非线性参数下存在稳定基态暗孤子和多极暗孤子的束缚态.另外,讨论了在局域自聚焦三次和非局域自散焦五次非线性介质中暗孤子和两极暗孤子的传输特性,发现孤子比在自散焦三次和自聚焦五次的非线性介质中传输更加稳定.进一步研究了单暗孤子和三极暗孤子的功率与传播常数和非局域程度的关系,并讨论了不同类型暗孤子的线性稳定性问题.     

Electromagnetically induced transparency and electromagnetically induced absorption in Y-type system

The propagation of a probe field through a four-level Y-type atomic system is described in the presence of two additional coherent radiation fields, namely, the control field and the coupling field. An expression for the probe response is derived analytically from the optical Bloch equations under steady state condition to study the absorptive properties of the system under probe field propagation through an ensemble of stationary atoms as well as in a Doppler broadened atomic vapor medium. The most striking result is the conversion of electromagnetically induced transparency(EIT) into electromagnetically induced absorption(EIA) as we start switching from weak probe regime to strong probe regime. The dependence of this conversion on residual Doppler averaging due to wavelength mismatch is also shown by choosing the coupling transition as a Rydberg transition.     

实现暗态的三芯耦合波导设计及其非线性脉冲传输特征

暗态效应被广泛应用于量子信息处理.通过纤芯结构的设计,在三芯耦合波导中实现了该量子效应,并数值研究了非线性对暗态的影响.研究发现,在几个耦合长度内,当波导1中的输入为归一化功率等于1的低能量光脉冲时,波导2与3中没有光传输;当入射光的归一化功率增大到1000时,波导2与3中依然没有明显光传输,且对比度超过4个数量级.然...