激光场线宽对四能级原子系统相干效应的影响

采用密度矩阵方程,在引入激光场线宽的条件下,计算了N型四能级原子系统中介质对探测场的吸收。结果表明:耦合场线宽的引入,消弱了四能级原子相干,对抑制吸收有增强作用,对增强吸收有抑制作用,即耦合场线宽的引入导致了退相干。控制场线宽的引入,在电磁感应透明中削弱了四能级原子相干性,降低了共振吸收,增强了光透明;在电磁感应吸收中,控制场线宽的增加使谱线中心两侧的吸收增强,削弱了谱线中心的吸收增强,从而使四能级系统的电磁感应吸收转换为电磁感应透明。     

微波场对电磁诱导透明谱的局域调制

当用两个微波场作用到Λ型三能级原子的耦合跃迁的基态与另两个超精细能态构成的跃迁时,由微波场诱导产生的两个高对比度共振吸收线将单重电磁诱导透明谱分裂成三个透明窗口。通过调节微波场的强度或失谐量,可实现对原子透明谱进行局域调制。采用缀饰态理论对展示的物理现象进行了解释。这些研究对多通道光通信和原子的可控调制等方面有一定的作用。     

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.     

The effect of Doppler broadening on dispersive and absorptive properties in atomic systems with two-photon interference

The effect of Doppler broadening on dispersive and absorptive properties is theoretically investigated in the hot four-level electromagnetically induced transparency (EIT) atomic systems with two different types of two-photon interference. It is found that the dispersive behavior for the probe in the ladder-type atomic system with two-photon constructive interference will be changed from anomalous in cold atoms to normal in hot atoms, and the three-peak absorptive profile is shifted to a broadened spectrum with a shallow dip at the line center; as a comparison, there is always normal dispersion at the line center for the invert-Y-type atomic system with two-photon destructive interference, but the EIT window in the absorptive profile will be narrowed to subnatural linewidth (0.01Γ) at room temperature. The physics of those two different behaviors are discussed and compared in the dressed-state theory.     

微波射频场调制下Λ型三能级原子系统的电磁感应光栅

研究了在微波射频场调制下的Λ 型三能级原子系统的电磁感应光栅现象. 结果表明: 微波场可以增强对探测场的相位调制和增益作用, 使得衍射强度、尤其是一阶衍射强度明显提高; 当系统参数取值适当时, 一阶衍射强度随微波场强度呈指数增长的趋势. 关键词： 电磁感应光栅 电磁感应透明 微波射频场     

Optical switching by controlling the double-dark resonances in a N-tripod five-level atom

We have investigated the optical switching in a five-level atom in a novel configuration of electromagnetically induced transparency. This N-tripod type level scheme combines the attractive features of cross-phase modulation appearing in N-type atoms with the ability to slow light pulses associated with tripod atoms. The addition of a new driving field to the usual tripod configuration allows to control the double-dark resonances which appear in the four-level tripod system and thus enables to manipulate the probe absorption and dispersion properties. We have studied the temporal dynamics of two pulses, a probe pulse and a switch propagating pulse through the sample. In the presence of the switching field, a deep in the absorption at resonance due to one-photon electromagnetically induced transparency appears and the atomic system is transparent to the probe field, which propagates at a very small group velocity. By tuning the fields, one of the usual double-dark resonances appearing in tripod system can be controlled (Stark-shifted) and the medium, which is transparent in the absence of the control field, will become highly absorptive. The linear and cross-phase modulation susceptibilities have been calculated and we predict the possibility to realize two-photon switching and giant cross-phase modulation. Finally we address the question about the generation of an entangled coherent state and we show that the giant cross-phase modulation provided by this N-tripod atomic system can be used for realizing polarization quantum phase gates.     

Electromagnetically induced transparency-like effect in the degenerate triple-resonant optical parametric amplifier

We investigate experimentally the absorptive and dispersive properties of the triple-resonant optical parametric amplifier (OPA) for the degenerate subharmonic field. In the experiment the subharmonic field is utilized as the probe field and the harmonic wave as the pump field. We demonstrate that the electromagnetically induced transparency (EIT)-like effect can be simulated in the triple-resonant OPA when the cavity linewidth for the harmonic wave is narrower than that for the subharmonic field. However, this phenomenon cannot be observed in a double-resonant OPA. The narrow transparency window appears in the reflected field. Especially in the measured dispersive spectra of the triple-resonant OPA, a very steep variation of the dispersive profile of the subharmonic field is observed, which can result in a slow light as that observed in an atomic EIT medium.     

四能级系统中相位控制电磁诱导透明研究

提出了一种利用微波场的相对相位调控电磁诱导透明(EIT)光谱特性的方法. 在外加双微波驱动场的准Λ型四能级原子系统中,通过求解系统的密度矩阵方程得到探测场的吸收谱,分析了电磁诱导透明窗口的位置随微波驱动场相位的变化规律,并借助缀饰态理论给出了准确解释. 结果表明,对于确定的作用场强度,调节微波驱动场的相位可实现电磁诱导透明的频率位置及间隔的准确控制. 关键词： 四能级原子系统 电磁诱导透明(EIT) 相位控制 微波场     

Absorptive reduction and width narrowing in Λ-type atoms confined between two dielectric walls

This paper investigates the absorptive reduction and the width narrowing of electromagnetically induced transparency （EIT） in a thin vapour film of A-type atoms confined between two dielectric walls whose thickness is comparable with the wavelength of the probe field. The absorptive lines of the weak probe field exhibit strong reductions and very narrow EIT dips, which mainly results from the velocity slow-down effects and transient behaviour of atoms in a confined system. It is also shown that the lines are modified by the strength of the coupling field and the ratio of L/λ, with L the film thickness and λthe wavelength of the probe field. A simple robust recipe for EIT in a thin medium is achievable in experiment.     

耦合场线宽：抑制电磁诱导吸收

原子相干对吸收的相长干涉导致电磁诱导吸收，这是一类新的相干效应. 以三个电偶极跃迁构成N型链，中间跃迁作为探测跃迁的四能级系统为例，揭示耦合场线宽抑制电磁诱导吸收的强度. 这并非与电磁诱导透明系统中耦合场线宽产生或者增强吸收的情形相矛盾，线宽仍然是抑制系统的相干性. 关键词： 电磁诱导吸收 耦合场线宽 原子相干 退相干     

Coherently induced grating in refractive index enhanced medium

We demonstrate a scheme for coherently induced grating based on a mixture of two three-level atomic species interacting with two standing-wave fields. As a result of interaction between the absorptive and amplified Raman resonances, the refractive index of the medium can be enhanced and modulated periodically. Then a sinusoidal grating, which can diffract the probe field into high-order directions, is coherently formed in the medium. The proposed scheme is theoretically investigated in a mixture of atomic isotopes of rubidium. The results show that the diffraction efficiency depends strongly on the two two-photon detunings of the two Raman transitions and the intensities of the two driving standing-wave fields.The proposed electromagnetically induced grating scheme may be applied to the all-optical switching and beam splitting in optical networking and communication.     

Electromagnetically induced self-imaging

We study the self-imaging and image-transforming properties of a probe field in a cold atomic medium with electromagnetically induced transparency (EIT). Due to the similarities between the gradient-index medium and the inhomogeneous index distribution of an EIT medium under the conditions of a negative probe detuning and a Gaussian control field, we find based on analytical investigations that there exists a kind of electromagnetically induced self-imaging phenomenon in cold atomic media. Numerical simulations clearly show that electromagnetically induced self-imaging is observable and controllable.     

Vacuum Rabi splitting for multilevel electromagnetically induced transparency system

We discuss the vacuum Rabi splitting (VRS) from multilevel atoms under electromagnetically induced transparency condition within the framework of linear absorption-dispersion theory. Sharp resonance features superimposed on usually occurring VRS doublet to three-peaked structure spectra are obtained here which can be engineered to have absorptive, dispersive, or dip like profiles according to the choice of system parameters such as radiative damping constants, atomic detunings and driving field strengths etc.Received: 23 June 2004, Published online: 24 August 2004PACS: 42.50.Pq Cavity quantum electrodynamics; micromasers - 42.50.Ar Photon statistics and coherence theory     

Phase control of squeezed state in double electromagnetically induced transparency system with a loop-transition structure

We theoretically study the squeezed probe light passing through a double electromagnetically induced transparency (DEIT) system, in which a microwave field and two coupling lights drive a loop transition. It is shown that the output squeezing can be maintained in both two transparency windows of DEIT, and it can also be manipulated by the relative phase of the three driving fields. The influence of the intensity of applied fields and the optical depth of atoms on the squeezing is also investigated. This study offers possibilities to manipulate the squeezing propagation in atomic media by the phase of electromagnetic fields.     

Electromagnetically induced transparency and lasing without inversion in three-level atoms imbedded in a frequency-dependent environment

The response of a three-level atomic system driven by a resonant coherent field acting on a transition near the photonic band-edge of a photonic band-gap material as well as the general case of a frequency-dependent reservoir is studied. The strong frequency dependence of the radiation mode spectral density on the scale of the driving field Rabi frequency is shown to lead to essential and controllable changes in the refractive index, as well as to effects of electromagnetically induced transparency and lasing without inversion. Such an effective dynamic control of the atomic response enables for applications in nonlinear optics and optical computing and communications.     

Quantum information processing with single photons and atomic ensembles in microwave coplanar waveguide resonators

We show that pairs of atoms optically excited to the Rydberg states can strongly interact with each other via effective long-range dipole-dipole or van der Waals interactions mediated by their nonresonant coupling to a common microwave field mode of a superconducting coplanar waveguide cavity. These cavity mediated interactions can be employed to generate single photons and to realize in a scalable configuration a universal phase gate between pairs of single photon pulses propagating or stored in atomic ensembles in the regime of electromagnetically induced transparency.     

Control of group velocity of light via magnetic field

We have theoretically studied the effects of quantum coherence in a driven quasi-degenerate two-level atomic system. We have shown that the quantum interference, which can be destructive or constructive, can be controlled by an externally applied magnetic field allowing one to implement both electromagnetically induced transparency and electromagnetically induced absorption in the same atomic system. Determined by frequency dispersion of the index of refraction of the system, the group velocity of light pulses ranges from ultra-slow to superluminal with changing of the magnitude of the magnetic field.     

冷85Rb原子D2线电磁诱导透明的实验研究

对85Rb原子D2线三能级系统的电磁诱导透明进行了详细的实验研究.得到了不同耦合强度下探测光的吸收线型,并对气室中热原子与磁光阱中冷原子的电磁诱导透明光谱进行了比较.     

四能级原子系统中的电磁诱导吸收

以三个电偶极跃迁(中间跃迁作为探测跃迁、两边分别是耦合跃迁和控制跃迁)构成N型四能级系统为例，研究介质对探测光的吸收.揭示了在N型四能级系统中，既可产生电磁诱导吸收又可产生电磁诱导透明.这不仅取决于非相干转移率的大小，而且还取决于耦合场、控制场的强度和第四个简并能级的衰减速率大小. 关键词： 电磁诱导吸收 电磁诱导透明 原子相干的自发转移 能级的衰减速率     

等离子体纳米结构中的Fano共振效应及其应用

Fano共振效应是一种具有非对称线型的共振散射现象,起源于共振过程和非共振过程的量子干涉效应。近年来,在等离子体纳米结构中Fano共振现象也被发现,并成为纳米光子学的一个研究热点。等离子体Fano共振通常具有较窄的光谱线宽,且不能直接与入射光耦合,只能局域在近场,强的近场局域特性可以获得巨大的表面电磁场增强。由于等离子体Fano共振独特的光学特性,已经被应用到单分子探测、高灵敏度传感、增强光谱、完美吸收、电磁诱导透明和慢光光子学器件等众多领域当中。