All-optical switching and storage in a four-level tripod-type atomic system

The optical behavior of a four-level tripod-type atomic system in a ring resonator driven by a cavity field and two external coherent fields is studied. It is shown that the atomic response exhibits an ultra-sensitive switch from high absorption to nearly transparency by changing the value of one of the control fields. The optical bistable response can be controlled by means of the external fields. The system can flip from the lower to the upper branch of the hysteresis curve without changing the incident probe. Switching and information storage of a light signal are predicted under appropriate triggering of the auxiliary external optical signals.     

Optical bistability using quantum coherence in a microwave-driven four-level atomic system

The behavior of the optical bistability (OB) is investigated in an optical system which consists of a four-level atomic system with a microwave drive field and an optical cavity. It is found that the optical bistability can be accomplished by adjusting different physical parameters in both steady and transient process. Due to the existence of the microwave drive field, the optical bistability can be also obtained even under weak coherent coupling field condition. Since the intensity and phase of microwave drive field can be conveniently modulated, this optical system provides a new experimental method to test the optical bistability theory.     

Coherent control of quantum entropy via quantum interference in a four-level N-type atomic system

The time evaluation of quantum entropy in a four-level N-type atomic system is theoretically investigated. Quantum entanglement of the atom and its spontaneous emission fields is then discussed via quantum entropy. It is found that the degree of entanglement can be increased by the quantum interference induced by spontaneous emission. The phase dependence of the atom-field entanglement is also presented.     

基于量子干涉效应的四能级原子系统中的vacuum-induced coherence效应

多能级系统中的vacuum-induced coherence(VIC)效应是一种重要的量子干涉效应，研究了VIC效应导致的系统电磁感应透明现象，并且改变了系统的吸收、增益和色散等性质，分析了在发生VIC效应时系统能级粒子数分布规律.另外，考虑复数拉比频率的相位变化时系统可呈现出光学双稳态效应.     

Spectral feature with sub-natural linewidth due to quantum interference in a four-level system

This paper studies the narrow spectral feature appearing in a four-level system coupled by two strong coherent fields and probed by a weak laser field. The linewidth is examined as a function of the Rabi frequencies of coupling fields, and the result is explained by using the dressed-state formalism.     

Controlling the optical bistability via quantum interference in a four-level N-type atomic system

We investigate the optical bistability (OB) and optical multi-stability (OM) in a four-level N-type atomic system. The effect of spontaneously generated coherence (SGC) on OB and OM is then discussed. It is found that SGC makes the medium phase dependent, so the optical bistability and multi-stability threshold can be controlled via relative phase between applied fields. We realize that the frequency detuning of probe and coupling fields with the corresponding atomic transition plays an important role in creation OB and OM. Moreover, the effect of laser coupling fields and an incoherent pumping field on reduction of OB and OM threshold is then discussed.     

Lasing without population inversion in a four-level Y-type configuration in double quantum dot system

Klein–Gordon equation is one of the basic steps towards relativistic quantum mechanics. In this paper, we have formulated fractional Klein–Gordon equation via Jumarie fractional derivative and found two types of solutions. Zero-mass solution satisfies photon criteria and non-zero mass satisfies general theory of relativity. Further, we have developed rest mass condition which leads us to the concept of hidden wave. Classical Klein–Gordon equation fails to explain a chargeless system as well as a single-particle system. Using the fractional Klein–Gordon equation, we can overcome the problem. The fractional Klein–Gordon equation also leads to the smoothness parameter which is the measurement of the bumpiness of space. Here, by using this smoothness parameter, we have defined and interpreted the various cases.     

四能级量子制冷循环

本文提出以两个qubit量子纠缠系统为工质的四能级制冷循环模型, 基于量子热力学第一定律和热纠缠概念, 分析了在循环中系统与外界交换的热量、输入功、制冷系数等热力学参数与量子纠缠之间的关系, 结果表明: 制冷系数等高线图是环状曲线, 随纠缠比r增加而非单调变化; 当相互作用常数J比较小时, 量子制冷机运行区间在c₁>c₂, 当增加J值时, 制冷机运行区间在c₁>c₂和 c₁<c₂两个区域; 最大制冷系数ε_max随J值增大而增加.     

Optical bistability and multistability in a four-level quantum system in the presence of plasmonic nanostructure

In this paper, the effect of plasmonic nanostructure on behavior of optical bistability and multistability in a four-level quantum system embedded in a unidirectional ring cavity has been studied. It is found that the distance between plasmonic nanostructures and a four-level quantum system is varied from 4.4 nm to 14.4 nm and has an essential role for controlling the threshold of optical bistability and multistability. Moreover, obtained results show that the group velocity of pulse propagation through the medium is strongly depended on the distance between the plasmonic nanostructure and the four-level quantum system.     

On geometric realization of quantum computations in an externally driven four-level system

The possibility of realization of quantum gates by means of the nonadiabatic geometric phase is considered. It is shown that the nonadiabatic phase can be used for realization of quantum gates as successfully as the adiabatic phase.     

Kerr non-linearity and four-wave mixing in a double-cascade type four-level system of multiple quantum wells

We study the non-linear optical response in multiple quantum wells structure with a double-cascade type four-level configuration based on excitons and biexcitons transitions. By analysing the Kerr non-linear effects, we obtain the slow, mutually matched group velocities and giant Kerr non-linearity of probe and signal fields. While when the signal (or probe) field is removed, the non-linear optical phenomenon four-wave mixing (FWM) originating from quantum interference is demonstrated. The FWM efficiency of the system study is about 50%. Such a semiconductor system is much more practical than its atomic counterpart because of its flexible design and the controllable interference strength.     

Optical solitons in a four-level inverted-Y system

With one weak probe field and two strong pumping fields, the possibility of producing superluminal optical solitons is discussed in a lifetime-broadened inverted-Y atomic medium with proper parameters. As the group velocity of the solitons is larger than c, its occurrence can be controlled by modulating the intensities and the detunings of lasers. PACS 42.50.-p; 42.65.-k     

Spontaneous emission from a four-level system

We examine the decay dynamics of a free four-level system in the -V configuration. Quantum interference strongly manifests itself in this system, as can be seen by looking at the combined spectral distribution of the two emitted photons and at the time evolution of the intermediate-level populations, whose effective lifetimes can become very long under certain conditions for the atomic parameters. This effect is attributable to a population transfer mechanism induced in the time evolution equations by the Fano terms, also responsible for the strong modifications of the spectral correlation between the emitted photons which we analyze in detail. Finally, population trapping can also occur when the two intermediate levels are degenerate. Received: 20 October 1998     

Controlling the probe-absorption and -dispersion via quantum interference from incoherent pumping field in a four-level lambda-type system

Absorptive and dispersive properties of a four-level Λ-type atomic system with two fold lower levels are investigated. The effect of quantum interference induced by incoherent pump and spontaneous emission upon the absorption, dispersion, and group index is them discussed. In addition, the rate of an incoherent pump field and the intensity of coupling field on light propagation is also presented.     

Lasing without inversion in a four-level diamond system

<正>We study the lasing without inversion in a four-level diamond configuration in the case of incoherent pumping field within the framework of the bare-state basis.With the strong fields limit,we obtain the approximate steady-state solution,and discuss the dependence of population distribution and system gain on probe detuning and auxiliary field Rabi frequency.     

Phase grating in a doubly degenerate four-level system

In this paper, we suggest a doubly degenerate four-level system, in which the transition takes place between the hyperfine energy 52S1/2 F = 1 and 52P3/2 F = 2 in rubidium 87 D2 line, for studying atomic phase grating based on the cross-Kerr and phase conjugation effects. The phase grating with high efficiency can be obtained by tuning phase shift Ф between the coupling and probe field, when the coupling intensity is much stronger than the strength of probe field. Under different coupling intensities, a high diffraction efficiency can be maintained. A new and simple way of implementing phase grating is presented. However, in such an atomic system, two main limitations must be taken into account. First, the independence between steady state probe susceptibility and the coupling intensity, when the population decay rate is larger than the Rabi frequency of the coupling field, cannot result in diffraction grating; second, the sample to be prepared should not be too long.     

Negative refractive index in a four-level atomic system

A closed four-level system in atomic vapour is proposed, which is made to possess left handedness by using the technique of quantum coherence. The density matrix method is utilized in view of the rotating-wave approximation and the effect of a local field in dense gas. The numerical simulation result shows that the negative permittivity and the negative permeability of the medium can be achieved simultaneously (i.e. the left handedness) in a wider frequency band under appropriate parameter conditions. Furthermore, when analysing the dispersion property of the left-handed material, we can find that the probe beam propagation can be controlled from superluminal to subluminal, or vice versa via changing the detuning of the probe field.     

Generation of two-photon correlation in a four-level system

We study the quantum correlation of a coherently foul-level atomic system coupled by two coherent driven fields. Used the wave function technique, an explicit expression of the photon-photon correlation function is derived. The influence of the driven field as well as the detuning on the second correlation function are investigated. We find that the second correlation function can be controlled by the driven field or the detuning of two coupling lasers. So we can control the magnitude of the joint detection probability by the driving fields. More importantly, we show that this correlated photon states can serve as atomic memory.     

Enhancement of four-wave mixing process in a four-level double semiconductor quantum well

The time-dependent four-wave mixing（FWM） is analyzed in a four-level double semiconductor quantum well. The results show that both the amplitude and the conversion efficiency of the FWM field are enhanced with increasing the strength of two-photon Rabi frequency. Interestingly, when the one-photon detuning becomes stronger the control field corresponding to the maximum efficiency increases. Such a controlled enhanced FWM may be used to generate coherent short-wave length radiation, and it can have potential applications in quantum control and communications.