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.     

铯原子气室中D2线泵浦探测光谱的实验观测

在铯原子气室中采用偏振方向相互垂直且同向传播的线偏泵浦光和探测光，研究了铯原子D2线的泵浦探测光谱。由于在6 S1/2 F=3 – 6 P3/2 F’=2 超精细跃迁中存在多个L型塞曼子能级结构，从而产生了电磁诱导透明导致的吸收减弱；而在6 S1/2 F=4 – 6 P3/2 F’=5 超精细跃迁中则观测到了电磁诱导吸收。通过改变泵浦光的失谐量，在电磁诱导透明形成的吸收减弱凹陷和电磁诱导吸收产生的吸收增强峰内部均观察到了反常的吸收信号反转。     

基于Rb原子电磁诱导透明的量子干涉实验研究

报道了基于85RbD2线电磁诱导透明(EIT)的量子干涉现象,发现当一耦合光和探测光之间满足拉曼共振条件时出现电磁诱导透明现象,在某些条件下也观察到电磁诱导吸收(EIA).而当用一束耦合光和一束泵浦光共同作用于5S1/2,F=3→5P3/2,F′=3和5S1/2,F=3→5P3/2,F′=4能级上时,探测光的吸收谱表现出三峰结构,并且峰强弱与两耦合光之间的相对强度有关.     

Study of width and height of EIT resonance in a Doppler broadened five-level system with varying probe power

We report the experimental observation of electromagnetically induced transparency (EIT) in a Doppler broadened rubidium vapour at room temperature for different probe intensities at a fixed pump intensity in a five-level Λ-type system formed by the D₂ transition of ⁸⁵Rb. For a constant pump intensity, we find that the EIT width and height change with the variation of probe intensity. We observe a nonlinear variation of the height of the EIT peak and a linear variation of the width (FWHM) of the EIT signal with probe intensity. In the Doppler broadened multilevel system, we also observe the velocity selective dips along with the EIT signal. A numerical simulation of the probe response signal based on density matrix representation in a five-level system is carried out to reproduce the experimentally observed spectra.     

Modulation transfer in Doppler broadened Λ system and its application to frequency offset locking

We investigate modulation transfer through pump induced atomic coherence in pump-probe spectroscopy of Doppler broadened medium of cesium atoms. The mechanism of modulation transfer is discussed for a three level Λ configuration under slow frequency modulation. Modulation transfer is demonstrated by performing frequency modulation spectroscopy (FMS) on a sub-natural linewidth (<2 MHz) electromagnetically induced transparency (EIT) signal. Here the pump laser is modulated by acousto-optic frequency modulation and the modulation is transferred to the probe laser through atomic coherence. Finally the probe laser is locked on the first derivative spectrum of EIT signal. Such atomic frequency offset locking system totally removes the necessity of direct modulation of laser frequency, so that the spectral resolution is limited only by the practical linewidth of the laser systems. Moreover it provides a novel way to eliminate the additional frequency and intensity noise associated with direct frequency dithering, which may limit the experimental resolution.     

Enhanced cross-phase modulation based on a double electromagnetically induced transparency in a four-level tripod atomic system

We report experimental observations on the simultaneous electromagnetically induced transparency (EIT) effects for probe and trigger fields (double EIT) as well as the enhanced cross-phase modulation (XPM) between the two fields in a four-level tripod EIT system of the D1 line of 87Rb atoms. The XPM coefficients (larger than 2 x 10(-5) cm2/W) and the accompanying transmissions (higher than 60%) are measured at a slight detuning of the probe field from the exact EIT-resonance condition. The system and enhanced cross-Kerr nonlinearities presented here can be applied to quantum information processes.     

On line shape of electromagnetically induced transparency in a multilevel system

We present a detail analysis of the line shape of electromagnetically induced transparency (EIT) in a Doppler broadened five level atomic system based on density matrix formalism. It has been shown that the velocity averaged EIT line shape in a multilevel system is very sharp. The effect of the ground state decay rates on the EIT peak has also been investigated. The linear and non-linear variations of the EIT line width (FWHM) for different pump and probe power ratios are shown. Considering the D₂ transition of ⁸⁵Rb atom the dependence of EIT width and height on pump power has been experimentally measured. Simulated spectra are compared with the experimentally obtained one. The effect of buffer gas on the EIT peak has also been observed experimentally as well as theoretically.     

射频驱动精细结构能级跃迁引起的非线性效应

研究了射频驱动精细结构能级跃迁引起的电磁诱导透明（EIT）和电磁诱导吸收（EIA）的转化。通过采用射频场同时驱动激发态和基态精细结构能级跃迁,使系统中出现EIT和EIA。研究结果表明,调谐射频场频率从与基态精细结构能级共振到与激发态精细结构能级共振的过程中,EIT和EIA相互转化,而且射频场的拉比频率取值不同,EIT和EIA的变化规律也不同。     

Y型四能级系统中Doppler展宽对真空诱导相干性相关的探测场吸收的影响

利用数值计算结果,讨论了在Y型四能级原子系统中Doppler展宽对与真空诱导相干性(VIC) 相关的探测场吸收性质的影响.研究结果表明: 当无Doppler展宽时,只有不存在VIC时才可能产生电磁感应透明(EIT)现象; VIC将导致探测场吸收的明显改变和增益产生;在VIC存在和不存在两种情况中,吸收曲线都具有关于探测场失谐对称的双峰结构. 当有Doppler展宽时,在VIC存在和不存在两种情况中都能产生EIT现象; VIC仍将导致探测场吸收的明显改变和增益产生;不管是否存在VIC,探测场吸收都具有以下特征:吸收曲线不再具有关于探测场失谐的对称性且随Doppler展宽宽度(D)值的增大而逐渐从双峰结构变为单峰结构,探测场吸收不随D值的增大而单调增大或减小,在探测场和驱动场的传播方向相反时可获得比传播方向相同时更小的探测场吸收.     

Observations of Autler-Townes spatial splitting of four-wave mixing image

We report the self- and external-dressed Autler-Townes (A-T) splittings of the images of the generated four-wave mixing signal (FWM) and electromagnetically induced transparency (EIT) of probe images in cascade three-level atomic system. Such spatial properties of probe and FWM signals are induced by the enhanced cross-Kerr nonlinearity. We demonstrate the controlled electromagnetically induced spatial dispersion (EISD), splitting and focusing of probe and FWM signals images by adjusting self- and external-dressing fields. Studies on such controllable A-T spatial splitting and spatial EIT effect can be very useful in applications of spatial signal processing and optical communication.     

Enhanced Deflection of Light Ray by Atomic Ensemble on Coherent Population Oscillation

In recent experiments [e.g., Nature Physics 2 (2006) 332], the enhancedlight deflection in an atomic ensemble due to inhomogeneous fields is demonstrated by the electromagnetically induced transparency (EIT) based mechanism. In this paper, we explore a different mechanism for the similar phenomenon of the enhanced light deflection. This mechanism is based on the coherent population oscillation, which leads to the hole burning in the absorption spectrum. The medium causing the deflection of probe light is an ensemble of two-level atoms manipulated by a strong controlled field on the two photon resonances. In the large detuning condition, the response of the medium to the pump field and signal field is obtained with steady state approximation. And it is found that after the probe field travels across the medium, the signal ray bends due to the spatial-dependent profile of thecontrol beam.     

Full Quantum Theory of Transient-State Electromagnetically Induced Transparency

We develop a full quantum theory of transient-state electromagnetically induced transparency (EIT) in the vapor of three-level A-type atoms interacting with probe and coupling lasers. As applications of the full quantum theory, we show that transient-state EIT medium exhibits normal dispersion and find that group velocities of both coupling and probe lasers are greatly reduced. It is shown that the group velocity of the probe laser in the transient-state EIT case is equal to that in the adiabatic EIT case and that the coupling laser group velocity in the transient-state EIT is generally less than that in the adiabatic EIT.     

Full Quantum Theory of Transient-State Electromagnetically Induced Transparency

We develop a full quantum theory of transient-state electromagnetically induced transparency (EIT) in thevapor of three-level A-type atoms interacting with probe and coupling lasers. As applications of the full quantum theory,we show that transient-state EIT medium exhibits normal dispersion and find that group velocities of both coupling andprobe lasers are greatly reduced. It is shown that the group velocity of the probe laser in the transient-state EIT case isequal to that in the adiabatic EIT case and that the coupling laser group velocity in the transient-state EIT is generallyless than that in the adiabatic EIT.     

Plasmon-induced absorption in stacked metamaterials based on phase retardation

In this paper, based on the constructive interference of plasmonic dipolar and quadrupolar modes, a classical analogue of electromagnetically induced absorption （EIA） is demonstrated theoretically in a stacked metamaterial consisting of a short metal strip （which acts as a bright resonator） and a long metal strip （acting as a dark resonator）, which has been reported to support the electromagnetically induced transparency （EIT） effect. The transition from EIA to EIT can be clearly observed in the absorbance spectra via varying the vertical spacing between two resonant oscillators. With the help of the coupled two-oscillator model, the phase shift between the bright and dark resonance modes is calculated by fitting the simulated absorbance spectra, which reveals the physical mechanisms behind constructive and destructive interference effects in EIT/EIA metamaterials.     

Coherent manipulation of light pulses in a multilevel atomic system

We consider the quantum memory process in general multilevel atomic systems with electromagnetically induced transparency (EIT). We discuss the pulse-matching phenomenon in this general EIT scheme. We also review a recent proposal to create tightly localized stationary pulses by using counterpropagating pump fields. The advantages in creating the stationary pulses with the general EIT system are also discussed.     

Squeezing and entanglement of a two-mode field in a four-level tripod atomic system

The interaction of a collection of N four-level tripod configuration atoms with two orthogonally polarized probe fields is investigated. Under the condition of electromagnetically induced transparency (EIT), we calculate the squeezing and entanglement spectra of the output probe fields. By analyzing the output spectrum, we find that the squeezing and entanglement of the probe fields can be well-preserved after passing through the optically thick medium. Additionally, the effects of the ground state dephasing rates of the atoms on the entanglement and squeezing of the output two-mode squeezed fields are investigated. It is shown that the dephasing rates will degrade the entanglement and squeezing, and these quantum properties can be lost when the dephasing rates increase up to a certain value. This will be useful in the quantum computation and quantum communication.     

Y型四能级系统中Doppler展宽对VIC相关的双光子吸收的影响

利用数值计算结果讨论了Doppler展宽对Y型四能级原子系统中真空诱导相干 性(VIC)相关的双光子吸收的影响. 研究结果表明: 1)在无Doppler展宽的情况中, 不存在VIC时, 吸收曲线具有双峰结构并产生电磁感应透明(EIT)现象, 存在VIC时吸收曲线具有单峰结构而EIT现象不再发生; 2)在有Doppler展宽的情况中, 不管是否存在VIC, EIT现象都能发生; 不存在VIC时, 不管探测场和驱动场传播方向相同还是相反, 随Doppler展宽宽度D值的增大, 吸收先增大后减小, 吸收曲线逐渐从双峰结构变为单峰结构; 存在VIC时, 若探测场和驱动场传播方向相同, 随D值的增大, 吸收先增大后减小, 吸收曲线逐渐从单峰结构变为双峰结构; 若探测场和驱动场传播方向相反, 随D值的增大, 吸收单调减小, 但吸收曲线仍保持单峰结构.     

Electromagnetically induced absorption and transparency in an optical-rf two-photon coupling configuration

We study electromagnetically induced absorption (EIA) and transparency (EIT) in an optical-rf two-photon coupling configuration. It is shown that the interference effect due to interacting dark resonances results in an EIA for a resonant two-photon coupling and this EIA is observed to evolve into an EIT when there is a detuning in the two-photon coupling.     

Monte Carlo simulations of electromagnetically induced transparency in a square lattice of Rydberg atoms

We study the steady optical response of a square lattice in which all trapped atoms are driven by a probe and a coupling fields into the ladder configuration of electromagnetically induced transparency(EIT). It turns out to be a manybody problem in the presence of van der Waals(vd W) interaction among atoms in the upmost Rydberg state, so Monte Carlo(MC) calculation based on density matrix equations have been done after introducing a sufficiently large cut-off radius. It is found that the absorption and dispersion of EIT spectra depends critically on a few key parameters like lattice dimension, unitary vd W shift, probe Rabi frequency, and coupling detuning. Through modulating these parameters, it is viable to change symmetries of the absorption and dispersion spectra and control on demand depth and position of the transparency window. Our MC calculation is expected to be instructive in understanding many-body quantum coherence effects and in manipulating non-equilibrium quantum phenomena by utilizing vd W interactions of Rydberg atoms.