Three-photon interference spectra in four-level atomic systems

We have considered the interference spectra that occur at the three-photon generated frequency arising from the interaction of three laser fields with a four-level atom, where two of the laser fields are on two-photon resonance with the three levels forming a “λ” scheme while the third laser operates between the second ground and the second excited state of the atom. At low intensities of all three laser fields, the overall intensity of the peak at the three-photon generated frequency, describing the spectrum of an electron in the second excited state, depends on the strength of the combined field of the two laser fields that are on two-photon resonance and it takes negative values. This indicates that light amplification without population inversion is likely to occur at the three-photon generated frequency. The combined field of the three laser fields induces multiphoton excitations near the three-photon generated frequency, whose peaks are characterized by linewidths which are much less than the natural linewidths of the atoms. These excitations describe absorption or stimulating emission processes depending on the values of the detunings of the laser fields. The derived results are graphically presented and discussed. Received: 24 January 2001 / Published online: 8 June 2001     

Dark resonances for ground-state transfer of molecular quantum gases

One possible way to produce ultra-cold, high-phase-space-density quantum gases of molecules in the rovibronic ground state is given by molecule association from quantum-degenerate atomic gases on a Feshbach resonance and subsequent coherent optical multi-photon transfer into the rovibronic ground state. In ultra-cold samples of Cs₂ molecules, we observe two-photon dark resonances that connect the intermediate rovibrational level |v=73,J=2〉 with the rovibrational ground state |v=0,J=0〉 of the singlet X ¹ Σ _g ⁺ ground-state potential. For precise dark resonance spectroscopy we exploit the fact that it is possible to efficiently populate the level |v=73,J=2〉 by two-photon transfer from the dissociation threshold with the stimulated Raman adiabatic passage (STIRAP) technique. We find that at least one of the two-photon resonances is sufficiently strong to allow future implementation of coherent STIRAP transfer of a molecular quantum gas to the rovibrational ground state |v=0,J=0〉.     

Resonance fluorescence spectrum of a three-level atom. II. Numerical results

Numerical computations are presented for the excitation spectra arising from the interaction between a three-level atom in the cascade configuration and a strong electromagnetic field whose frequency mode is initially populated. The excitation spectra are considered when the laser field is at resonance with the equally spaced levels of the atom as well as a function of the detunings. The physical process of optical amplification occurs without population inversion and it is more pronounced when the laser field is detuned than when it is at resonance. The shapes of the spectral lines for a number of side-bands are of the absorption-amplification type rather than that of the absorption one. In the presence of detunings as well as in the cooperative two-photon cascade process, the resulting spectra are far more complicated than those occuring at resonance. Results of numerical calculations for a wide range of Rabi frequencies and detunings are presented graphically.     

Cascade Two-photon Correlated-emission Optical Bistability

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用于铯原子受激拉曼绝热输运过程的光源的产生

受激拉曼绝热输运(STIRAP)是一种有效制备和控制原子态的技术,在原子操控和量子信息中具有重要意义,最近几年得到广泛关注.研制用于特定原子的拉曼激光是实现该过程的重要一步.研究了利用光纤波导调制器及干涉滤波器等组成的系统实现用于铯原子STIRAP过程的光源的方法.通过直接调制高频光纤调制器获得正负一级边带,并利用两个...     

STIRAP transport of Bose-Einstein condensate in triple-well trap

The irreversible transport of multi-component Bose-Einstein condensate (BEC) is investigated within the Stimulated Raman Adiabatic Passage (STIRAP) scheme. A general formalism for a single BEC in M-well trap is derived and analogy between multi-photon and tunneling processes is demonstrated. STIRAP transport of BEC in a cyclic triple-well trap is explored for various values of detuning and interaction between BEC atoms. It is shown that STIRAP provides a complete population transfer at zero detuning and interaction and persists at their modest values. The detuning is found not to be obligatory. The possibility of non-adiabatic transport with intuitive order of couplings is demonstrated. Evolution of the condensate phases and generation of dynamical and geometric phases are inspected. It is shown that STIRAP allows to generate the unconventional geometrical phase which is now of a keen interest in quantum computing.     

Local Control of Two-Photon Absorption in a Six-Level Atomic System by Using a Coherent Perturbation Field

If a coherent perturbation field is used to couple the excited level of thecoupling transition in the five-level K-type atom with another higher excitedlevel, the two-photon electromagnetically induced transparency can belocally modulated by altering the parameters of the additional perturbationfield. With different detunings of the coherent perturbation field, theabsorption peak or transparency window with sharp and high-contrast spectral feature can be generated in the two-photon absorption spectrum. The physical interpretation of these phenomena is given in terms of the dressed states.     

激光诱导的四能级系统电子布居转移H

受激拉曼绝热通道(STIRAP)为我们提供了一种有效转移原子与分子中电子布居的方法.采用数值方法系统地分析了不同的四能级系统在受激拉曼迁移过程中电子布居的转移情况,计算了各种系统处于双光子共振和共振失谐时的转移率,并且讨论了在不同情况下第四能级对转移率的影响.计算结果表明,对于许多原子或分子系统,获得高的转移率所必须满足的条件是非常严格的,而有些四能级系统根本就不能获得高的转移率.(     

Laser-excited nonlinear properties of BaF2 and its application in a single-shot spatially insensitive autocorrelator

A detailed investigation of laser-generated nonlinear processes of undoped barium fluoride is presented including two-photon-excited exciton fluorescence, color-center formation and damage-threshold measurements. A single-shot autocorrelator based on two-photon fluorescence of BaF₂ was constructed to measure the phase and amplitude of pulses provided by large apeture excimer lasers. The capabilities of the autocorrelator are demonstrated at 248 nm and 268 nm with pulses in the regime of 100 fs to 10 ps.     

Cluster-type entangled coherent states

We present the cluster-type entangled coherent states (CTECS) and discuss their properties. A cavity QED generation scheme using suitable choices of atom-cavity interactions, obtained via detunings adjustments and the application of classical external fields, is also presented. After the realization of simple atomic measurements, CTECS representing nonlocal electromagnetic fields in separate cavities can be generated.     

COHERENT POPULATION TRAPPING IN MULTILEVEL LASER-INDUCED CONTINUUM STRUCTURE SYSTEM INCLUDING CASCADE TWO-PHOTON PROCESSES

We have investigated the atomic coherent population trapping in a mul tilevel laser-induced continuum structure system including cascade two-photon processes, in which two sets of quasicontinua of excited levels to be modeled as the Bixon-Jortner quasicontinuum are laser-embedded into a previously structu reless atomic continuum.The condition leading to the atomic coherent population trapping and the coherent population trapping state are given explicitly. And th e effects of the Fano factors, the laser intensities and the detunings on the am ount of population trapped in the atomic bound states and the populations distri buted in the two sets of quasicontinua are also examined.     

简并双光子激光:无反转激光和无激光反转

在原子衰减常数相等、单光子失谐不太大且饱和不太深的条件下，对于两个适当的原子－场耦合常数，简并双光子激光系统一方面能够呈现无反转激光，另一方面又能够呈现无激光反转。 关键词：     

Ultraslow bright and dark optical solitons in a cold three-state medium

We show the formation of ultraslow bright and dark optical solitons in a lifetime-broadened three-state atomic system under Raman excitation. We also discuss why such ultraslow optical solitons may not exist under the conditions of the usual electromagnetically induced transparency configuration where zero one- and two-photon detunings are required.     

Study on three level system population transfer

Stimulated-Raman-adiabatic-passage (STIRAP) process provides an effective technique to transfer electron population from an initial state (e.g. ground state) to excited final state for both atoms and molecules. In this paper, we present the results of the study on electron population transfer in three level system. We have analyzed the effects of various conditions on the transfer process, such as the time delay of the two laser beams, two-photon off-resonance, one-photon off-resonance and the change of relative laser intensity. The numerical result is compared with experiment, and the reasons for the effects are also given.     

Numerical study of the spiking instability caused by modulation frequency detuning in an actively mode-locked solid-state laser

We have studied both analytically and numerically the transient active mode locking in the case of a modulation frequency detuning. Analytical results for pulse width and position, extending previous works, are obtained within the frame of the stationary theory by assuming that a short pulse restores its shape after each round trip. Numerical evaluation leads to relaxation oscillations and change of the short-pulse shape. The results of both approaches agree with each other only for small detunings, when laser is operated in the steady state. For larger detunings the laser dynamics change dramatically, and the three operation modes observed earlier in experiments were demonstrated numerically: sequences of damped relaxation oscillations, deep periodic spiking and chaotic spiking. The periodic spiking can be used to increase the intensity of mode-locked pulses.     

Efficient Population Transfer in a Λ-Type Quantum System Coupled to a Gold Nanoparticle Using STIRAP Shortcuts

A theoretical investigation on the population transfer in a Λ-type quantum system near a spherical gold nanoparticle under application of two stimulated Raman adiabatic passage (STIRAP) shortcuts and efficiency comparison with conventional STIRAP. It combines the density matrix approach for system dynamics, with classical electromagnetic calculations used to obtain the modified electric field amplitudes of the applied pulses and the Purcell factor of the quantum system due to the presence of the nanoparticle. The efficiency of population transfer is investigated by varying the distance between the quantum system and the nanoparticle, the free-space decay rate of quantum states, the mutual polarization, and the Rabi frequencies of each STIRAP shortcut pulses. In all cases, at least one of the applied shortcuts is more efficient than conventional STIRAP, while in most cases both perform better. When the pump and Stokes fields of the shortcuts have radial and tangential polarizations with respect to the nanoparticle surface, respectively, high transfer efficiency is obtained for small distances of the quantum system to the nanoparticle, moderate free space decay rates and large Rabi frequencies of the fields, while when the pulse polarizations are interchanged, the transfer becomes highly efficient only at large distances.     

Probe spectroscopy of three-level systems with a standing-wave saturator: Influence of the saturator detuning

The absorption of a weak laser beam probing a Doppler-broadened three-level system saturated by a standing-wave pump is studied theoretically for the case of small saturator detunings. The features of the obtained absorption spectra are analysed by means of the dressed-atom approach. A strong influence of radiative and high-order multi-photon processes is showed. The influence of saturator tuning fluctuations on the narrow Doppler-free peak which appears in the resonant case is analysed and its consequences for high-resolution applications are considered.     

Entanglement sudden death of two atoms interacting with a cavity via the two-photon process in a strong-driving-assisted system

We examine the entanglement dynamics between two strongly driven atoms off-resonantly coupled with a single-mode cavity via the two-photon process with the help of negativity in two different types of initial states. The results show that entanglement sudden death may occur under both the above conditions and the sudden death effect can be monitored by modulating the atom--cavity detunings. Furthermore, we also find an atomic decoherence-free subspace so that the initial entanglement between two atoms remains invariable in application.     

Stimulated Raman adiabatic passage in fields with stochastic amplitudes

A theoretical analysis is presented of the effect of correlation between fluctuations of laser pulse amplitudes on population transfer between the states of a three-level atom coupled by the laser field. The carrier frequencies of the pulses are tuned to resonance with the transitions between the ground and excited states, |〈 and | 2〈, and the excited and metastable states, |2〈 and |3〈, in a lambda-type configuration. The laser pulses are timed so that population transfer between states |1〈 and | 3〈 is made possible by stimulated Raman adiabatic passage (STIRAP) in the absence of fluctuations. STIRAP does not occur when the laser fields are not correlated. When the fluctuations of one pulse amplitude duplicate those of the other, STIRAP can be observed for pulse amplitudes larger than those required in the absence of fluctuations.