Nonlinear dynamics study of an open resonant Λ-type system

Quantum coherence and interference in atomic systemshave a number of important consequences, includinglasing without inversion (LWI), the electromagneticallyinduced transparency, coherent population trapping, thesubrecoil cooling of atoms, potentiality for sensitive mea-surements of magnetic fields, and so on. In particular,LWI has attracted much more attention[1-12] and havebeen studied in the past few decades. The open Λ-typethree-level system for LWI is proposed[13-14]. From thenonline…     

Enhancement of coherent population transfer in a double Λ-type four-level system via a train of pulse pairs

We propose a flexible way to significantly enhance population transfer efficiency with a train of time-separated pump-Stokes pulse pairs when the non-adiabatic coupling between two degenerate adiabatic states exists in a double Λ-type four-level system, where the pump and Stokes pulses in each pair can be applied in either counterintuitive or intuitive order. It is shown that the needed Rabi frequency for achieving complete population transfer can be reduced dramatically with the increase of number of pump-Stokes pulse pairs, which results from temporal constructive quantum interference between the sequential transitions and subsequent coherent accumulation; moreover, an arbitrary coherent superposition between the two lower states can be realized by suitably tuning the Rabi frequency and the time delay between each pump-Stokes pair. The method may find applications in control of chemical reactions, quantum optics, and quantum information processing.     

Controlling the optical bistability in a Λ-type atomic system via incoherent pump field

We investigated optical bistability (OB) and the absorption properties of a weak probe field in a three-level Λ-type atomic system confined in a unidirectional ring cavity via incoherent pump field. We found that the threshold of OB and the probe field absorption can be controlled by the rate of incoherent pump field. No laser field was used in the pumping processes.     

Phase-controlled atom-photon entanglement in a three-level Λ-type closed-loop atomic system

We study the entanglement of dressed atom and its spontaneous emission in a three-level Λ-type closed-loop atomic system in a multi-photon resonance condition and beyond it.It is shown that the von Neumann entropy in such a system is phase-dependent,and it can be controlled by either the intensity or relative phase of applied fields.It is demonstrated that for the special case of the Rabi frequency of applied fields,the system is disentangled.In addition,we take into account the effect of Doppler broadening on the entanglement and it is found that a suitable choice of laser propagation direction allows us to obtain the steady state degree of entanglement(DEM) even in the presence of the Doppler effect.     

Dynamic control of retrieval contrast in a Λ-type atomic system

We propose an efficient scheme for optimizing the optical memory of a sequence of signal light pulses in a system of ultracold atoms in Λ configuration. The memory procedure consists of write-in, storage, and retrieval phases. By applying a weak microwave field in the storage stage, additional phase-dependent terms are included, and the contrast of the output signal pulses can be dynamically controlled (enhanced or suppressed) through manipulating the relative phase φ between optical and microwave fields. Our numerical analysis shows that the contrast is enhanced to the most extent when φ=1.5π. In addition, the contrast is in proportion to the Rabi frequency of the microwave field with a certain relative phase.     

Kramers–Kronig relation in a Doppler-broadened Λ-type three-level system

We measure the absorption and dispersion in a Doppler-broadened Λ-type three level system by resonant stimulated Raman spectroscopy with homodyne detection. Through studying the dressed state energies of the system, it is found that the absorption and dispersion satisfy the Kramers–Kronig relation. The absorption and dispersion spectra calculated by employing this relation agree well with our experimental observations.     

Phase control in an open Λ-type system with spontaneously generated coherence

This paper investigates the control role of the relative phase between the probe and driving fields on the gain, dispersion and populations in an open A system with spontaneously generated coherence （SGC）. It shows that by adjusting the value of the relative phase, a change from lasing with inversion to lasing without inversion can be realized; the values and frequency spectrum regions of the inversionless gain and dispersion can be obviously varied; high refractive index with zero absorption and electromagnetically induced transparency can be achieved. It is also found that when the driving field is resonant, the shapes of the dispersion and the gain curves versus the probe detuning are very similar if the relative phase of the dispersion lags π/2 than that of the gain, however for the off-resonant driving field the similarity will disappear; the gain, dispersion and populations are periodical functions of the relative phase, the modulation period is always 2π; the contribution of SGC to the inversionless gain and dispersion is much larger than that of the dynamically induced coherence.     

Unexpected Population Inversion in a Λ-type Medium

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Calculation of the binding energy and of the parameters of low-energy scattering in the Λnp system

The cluster-reduction method is used to solve the differential Faddeev equations for S=1/2, T=0 and S=3/2, T=0 spin-isospin states of the Λnp system in the s-wave approximation. The NN interaction is simulated on the basis of the MT I–III potential model, and the ΛN potential is set to V _ΛN =V _NN /2. This simple option makes it possible to reproduce faithfully the binding energy of the hypertriton _Λ ³ H. The doublet and quadruplet Λd scattering lengths and the low-energy phase shifts are calculated. It is shown that the effective-range approximation is applicable to the cases of doublet and quadruplet scattering.     

Optical bistability and multistability via atomic coherence in the quasi-Λ-type atomic system

The steady-state optical bistability (OB) and optical multistability (OM) behavior in the quasi-Λ-type atomic system driven by a probe field and a coherent coupling field inside a unidirectional ring cavity are shown, and the effects of coupling-field detuning and coupling-field intensity on the OB and OM behavior are investigated. The transition from OB to OM or vice versa is found by varying the detuning of the coherent coupling field or by adjusting the intensity of the coupling field. The influence of the atomic cooperation parameter on the OM behavior is also discussed. Supported by the Natural Science Foundation of Jiangxi of China (Grant No. 2007GZW0819), the National Basic Research Program of China (Grant No. 2005CB724508), and the Foundation of Talent of Jinggang of Jiangxi Province (Grant No. 2008DQ00400)     

Transient absorption–dispersion properties of four-level atomic system via elliptically polarized probe light and magnetic field

A novel four-level atomic system which interacted by an elliptically polarized probe field and a control laser field in the presence of external magnetic field is proposed. Here, we are interested in the transient properties of a weak probe field due to its potential application on quantum computing and quantum communication. It is shown that the external magnetic field and relative phase between two electric field components of the probe field can influence the probe absorption and dispersion.     

Optical bistability and multistability in a three-level Δ-type atomic system under the nonresonant condition

Under a nonresonant condition, we theoretically investigate hybrid absorptive-dispersive optical bistability and multistability behaviours in a three-level Δ-type system by using a microwave field to drive a hyperfine transition between two upper excited states inside a unidirectional ring cavity. We find that the optical bistability and multistability behaviours can be controlled by adjusting the intensity of the microwave field or the intensity of the coherent coupling field. Furthermore, our studies show an interesting phenomenon of the transition from the optical bistability to the optical multistability only by changing the negative detuning of the coupling field into the positive detuning of the coupling field.     

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.     

Effect of four-wave mixing on electromagnetically induced transparency in Λ-type system with a two-photon probe field

Using density matrix equation, we calculate analytically as well as numerically the effect of the four-wave mixing (FWM) field on electromagnetically induced transparency (EIT) in the rubidium 5S_{1/2}-5P_{3/2}-5D_{5/2} Λ-type system with a two-photon probe field. The calculated results are in good agreement with Fulton's experimental results in 1995 Phys. Rev. A 52 2302.     

Soliton management in the nonlinear Schrödinger equation model with varying dispersion, nonlinearity, and gain

The novel stable “soliton islands” in a “sea of solitary waves” of the nonlinear Schrödinger equation model with varying dispersion, nonlinearity, and gain or absorption are discovered. Different soliton management regimes are predicted.     

The influence of spontaneously generated coherence on atom-photon entanglement in a Λ-type system with an incoherent pump

Owing to interference induced by spontaneous emission, the density-matrix equations in a three-level Λ-type system have an additional coherence term, which plays a critical role in modulating the inversionless gain and electromagnetically induced transparency effect. In addition, it is shown that spontaneously generated coherence (SGC) has an effect on the entanglement between an atom and a photon of the coupling laser field by calculating the degree of entanglement (DEM) of the atomic system. In this paper, we investigate the influence of the SGC effect on atom-photon entanglement in a Λ-type system, which generally remains a high entangled state. When an incoherent pump source is introduced, we find that the SGC effect could exert considerable influence on the atom reduced entropy under certain conditions for both transient and steady states. More interestingly, such an incoherent pump field could actively affect the short-time dynamic behaviors of the transient quantum entangled state at a certain range of pump rate as a typical coherent case.     

Dynamical control of population and entanglement for open Λ-type atoms by engineering the environment

The exactly analytical solution for the dynamics of the dissipative Λ-type atom in the zero-temperature Lorentzian environment is presented. On this basis, we study the evolution of the population and entanglement. We find that the stable populations on the two lower levels of the Λ-type atom can be effectively adjusted by the combination of the relative decay rate and the environmental spectral frequency. However, for the initial Werner-like state, the stable entanglement between the two Λ-type atoms has very little tunability. Furthermore, the stable entanglement for the bilateral environment case is larger than that of the unilateral environmental case. A nonintuitive relation between the stable entanglement and stable population is found.     

Causality principle and nuclear dispersion anomaly in the elastic scattering for α+12C system

The optical model analysis of the alpha particle elastic scattering on a carbon target was performed on the basis of the dispersion relation between the real and imaginary parts of the calculated volume integrals. A nuclear dispersion anomaly in an α+12C system was observed and interpreted clearly.     

Impurity effects of the Λ hyperon in the hypernuclear systems Λ25Mg and Λ29Si

Based on the beyond-mean-field Skyrme-Hartree-Fock model,impurity effects of the Λ hyperon in the hypernuclear systems Λ25Mg and Λ29Si are investigated,respecti...     

Spontaneous emission spectrum and level splitting of a three-level Λ-type atom in a damped cavity

We study the spontaneous emission spectrum of a three-level Λ-type atom in a damped cavity using the resolvent operator. The shape of the spectrum is strongly influenced by the detuning and the coupling intensity between the atom and the cavity mode. Especially, we find that the splittings of the upper level of the three-level Λ-type atom are different in strong coupling regime, intermediate coupling regime and weak coupling regimes.