Self-induced transparency in a resonance medium with the dipole-dipole interaction

Propagation of a pulse of self-induced transparency in a resonance medium is discussed for the case when it is necessary to take into account the direct electric dipole-dipole interaction between atoms. An equation for the envelope of a wave packet—the sine-Gordon equation—is obtained for the case of durations short compared to ω ₀ ^?1 (ω₀ is the transition frequency). The dependence of the velocity and the amplitude of the soliton on the magnitude of the dipole-dipole interaction of atoms is examined in the adiabatic approximation.     

Probing electronic coherence in a gas of dipole-dipole coupled Rydberg atoms

We demonstrate a novel time-domain method to probe electronic coherence in ensembles of cold Rydberg atoms coupled via nearly resonant dipole-dipole interactions. Short laser pulses create coherent superpositions of few-electron eigenstates which evolve under the influence of pulsed electric fields. The pulses steer the dynamics, enhancing the probability for finding atoms in np, rather than initially excited ns states. The enhancement reflects the underlying electronic coherence which persists for >10 μs, 2?orders of magnitude longer than previously measured dephasing times in the same system. Simulations suggest that atom motion is responsible for the eventual decoherence.     

Optical bistability induced by quantum coherence in a negative index atomic medium

Bistability behaviors in an optical ring cavity filled with a dense V-type four-level atomic medium are theoretically investigated. It is found that the optical bistability can appear in the negative refraction frequency band, while both the bistability and multi-stability can occur in the positive refraction frequency bands. Therefore, optical bistability can be realized from conventional material to negative index material due to quantum coherence in our scheme.     

Incoherent pump influence on the transient gain in a V-type system with spontaneously generated coherence

We study the influence of the incoherent pump field on the transient response of a three-level V-type system with two near-degenerate excited states. In this system due to interaction of the field with the vacuum an interference term appears, the spontaneously generated coherence term. We find that due to the incoherent pump the transient proprieties of the atomic system can be significantly modified. The enhancement of the transient gain can be obtained for proper values of the rate of the incoherent pump field and relative phase between the two fields.     

Subluminal to superluminal light propagation in a V-type three-level atomic system interacting with squeezed vacuum

We study the light propagation properties in a V-type three-level atomic system interacting with two independent broadband squeezed baths. Using the graphic method, the dependences of the absorption and the dispersion of the system on the coupling field strength, the incoherent pumping field strength and the intensity of the squeezed vacuum are analysed. The result shows that the probe pulse propagation can be changed from subluminal to superluminal speed.     

Electromagnetically induced left handedness in a V-type four-level atomic system

A closed four-level system in atomic vapor is proposed, which is made to possess left handedness by means of the technique of quantum coherence. The method of density matrix is utilized in view of the rotating-wave approximation and the effect of local-field in dense gas. The result of the numerical simulation shows that the negative permittivity and 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 analyzing the dispersion property of the left-handed material, we find that the probe beam can be controlled to change from superluminal to subluminal or vice versa via changing the detuning of the probe field.     

Enhanced nonlinear generation in a three-level medium with spatially dependent coherence

We consider a method for efficient parametric generation of a laser pulse. A single laser field is injected into a three-level medium that has two lower states and one excited state. The lower states are initially prepared in a position-dependent coherent superposition state. It is shown that, by proper choice of the position dependence of the superposition along the direction of propagation, the incoming field can be completely converted to a new field.     

Lasing with and without inversion due to spontaneously generated coherence in an open V-type system

It is shown that in an open V-type atomic system without incoherent pumping, the spontaneously generated coherence (SGC) can not only lead to lasing with inversion but also lead to lasing without inversion (LWI)including at resonance of the driving and probe fields. This conclusion is much different from that obtained in the corresponding closed V-type system.     

在V型系统中原子相干对吸收—色散关系的影响

在V型能级系统原子介质中,若利用外场产生相干,则弱光场在该介质中的吸收-色散关系将展现出新的特性.特别是当弱场具有某一特定频率时,介质对光的吸收为零但光折射率大于1.     

Reverse-saturated absorption and narrow line in the absorption spectrum of a V-type three-level medium

We study the absorption spectrum of a V-type three-level atom when the laser beam interacts only with one of its two transitions. With the presence of vacuum-induced quantum interference, the absorption spectrum shows some new interesting features, which include ultranarrow absorption line, transparency, and a reverse-saturated absorption that is characterized by a larger absorption with increasing laser intensity.     

The optical properties of a V-type atomic medium driven by an additional field

The effects of an additional level and field on the dispersion and absorption characteristics of a four-level atomic medium based on a V-type are studied. The steady state solutions are given under two different fourth level damping rate relations, with the tunable weak probing field and resonant coupling and driving fields.     

Fidelity of quantum information for V-type three-level atom interacting with a number state light field in Kerr medium

In this paper the evolution characteristics of the fidelity of quantum information for the V-type three-level atom interacting with number state light field in Kerr meddium are investigated. It shows that the periodicity of the evolutions of fidelity of quantum information is influenced by the Kerr coefficient, the photon number of the initial field and intensity of light. The evolutions of the fidelity of quantum information are modulated by the initial number state field. The Rabi oscillation frequency and the modulation frequency of fidelity for the field and the system vary with the value of the Kerr coefficient. The evolutions of fidelity of quantum information obviously show the quantum collapse and revival behaviours in the system of atom interacting with light field.     

Optical light storage in an ensemble of V-type atoms mediated by vacuum induced coherence

We examine the possibility to write, store and retrieve light pulses into an ensemble of V-type three-level atoms where quantum interference of the spontaneous emission from the two upper states is accounted for. It is shown that the adiabatic change of the splitting of the two upper states can be used as a knob to transfer the electromagnetic excitation into a certain combination of coherences. The quantum properties of the mapping are also analyzed. The feasibility of obtaining such a process in a solid state system, where Fano-interferences mimic the vacuum induced coherence produced in atomic system is considered.     

真空诱导相干对电磁感应左手效应的影响

研究了具有超精细结构的四能级原子系统在电磁感应下的左手效应.讨论了由交叉耦合自发辐射路径引起的真空诱导相干(VIC)对左手效应的影响.研究表明,在出现左手效应的频率区间VIC效应强弱对介质相对介电常数和相对磁导率实部取值有显著影响,介质的左手效应随VIC效应的增强而增强. 关键词： 量子干涉 真空诱导相干 电磁感应 左手效应     

Thermodynamic limit for a system with dipole-dipole interactions

The free energy at constant magnetization of a simple cubic lattice of Ising spins with dipole-dipole interactions in periodic boundary conditions is related to the free energy at constant magnetization with no periodicity. The relationship is not one of equality.     

Oscillations of echo amplitude in glasses in a magnetic field induced by nuclear dipole-dipole interaction

The influence of a magnetic field on the dipole echo amplitude in glasses (at temperatures of about 10 mK) induced by the dipole-dipole interaction of nuclear spins has been theoretically studied. It has been shown that a change in the mutual position of nuclear spins at tunneling and the Zeeman energy E _H of their interaction with the external magnetic field lead to a nonmonotonic magnetic-field dependence of the dipole echo amplitude. The approximation that the nuclear dipole-dipole interaction energy E _d is much smaller than the Zeeman energy has been found to be valid in the experimentally important cases. It has been shown that the dipole echo amplitude in this approximation may be described by a simple universal analytic function independent of the microscopic structure of the two-level systems. An excellent agreement of the theory with the experimental data has been obtained without fitting parameters (except for the unknown echo amplitude).     

Preservation of coherence for a two-level atom tunneling through a squeezed vacuum with finite bandwidth

Tunneling of a two-state particle through a squeezed vacuum is considered. It has been shown that repetitive measurement or interaction with the external field can preserve the coherence. Moreover, the coherence time in terms of the squeezing parameters has been calculated. A specific condition is derived, under which the coherence is sustainable.