Enhanced Kerr nonlinearity via atomic coherence in a three-level atomic system

We measure the Kerr-nonlinear index of refraction of a three-level Lambda-type atomic system inside an optical ring cavity. The Kerr nonlinearity is modified and greatly enhanced near atomic resonant conditions for both probe and coupling beams. The Kerr nonlinear coefficient n(2) changes sign when the coupling beam frequency detuning switches sign, which can lead to interesting applications in optical devices such as all-optical switches.     

Generation of entanglement via atomic coherence in a two-mode three-level cascade atomic system

The generation of continuous variable entanglement via atomic coherence in a two-mode three-level cascade atomic system is discussed according to the entanglement criterion proposed by Duan et al. [Phys. Rev. Lett. 84, 2722 (2000)]. Atomic coherence between the top and bottom levels is induced with two photons of a strong external pump field. It shows that entanglement for the two-mode field in the cavity can be generated under certain conditions. Moreover, by means of the input-output theory, we show that the two-mode entanglement could also be approached at the output.     

Multicolor coherence-induced negative refraction in three-level atomic system

Multicolor manipulation of negative refraction in a three-level Λ atomic system is theoretically investigated. Based on multicolor coherence, the negative refractive index can be obtained with reduced absorption. The refractive index can also be controlled by changing the sum of the phases of the sidebands in the trichromatic driving fields. By adjusting the sum phase, the refractive index can be varied between negative and positive in two different frequency bands. Furthermore, the frequency band corresponding to the negative refractive index is widened by increasing the intensity and the frequency difference of the trichromatic field.     

A semi-classical approach to two-frequency solitons in a three-level cascade atomic system

A semi-classical theory of two intense optical fields interacting with a third-order non-linear medium composed of a three-level cascade atomic system is presented. It is predicted that non-linear atom-field interactions allow the formation of two-frequency bright, dark and grey spatial solitons. We demonstrate through numerical simulations and analytic stability analysis that the bright and grey solitons are stable.     

Observation of polarization-controlled spatial splitting of four-wave mixing in a three-level atomic system

We report experimental observations of intensity modulation and spatial splitting of four-wave mixing (FWM) signal beams which can be effectively controlled by the polarization states of the pumping laser beams. Due to the periodic change of the pumping beam’s polarization states, the intensity of the FWM beam also evolves periodically. The periodic spatial splitting phenomenon has been observed in both x- and y-directions. The cases with/without the dressing beams are compared. Such studies can be very useful in better understanding the formation of spatial solitons and for signal processing applications, such as spatial beam splitter, routing, and switching.     

Coexisting four-wave mixing and six-wave mixing in three-level atomic system

We demonstrate the coexisting four-wave mixing (FWM) signal and six-wave mixing (SWM) signal which can be enhanced both by electromagnetically induced transparency (EIT) and optical pumping effect in a common three-level and open four-level inverted-Y type systems of ⁸⁵Rb. We also analyze the effect of optical pumping in different energy level systems by arranging laser beams and comparing the strength of the increased and reduced absorption caused by optical pumping.     

Evolution of population in an equispaced three-level ladder-type atomic system

Transient response of nearly equispaced three-level ladder-type atomic system with a broad-band squeezed vacuum (SV) is investigated. We focus our attention in the interplay between the quantum interference and the squeezed field on the population distribution. It is shown that an atomic population inversion can be attained on one of the optical transitions due to the SV. Additionally, we show, with the proper value of the relative phase, the SV can also lead to unexpected population inversion on the transition between two different levels.     

Dependence of enhanced Kerr nonlinearity on coupling power in a three-level atomic system

We study the enhanced Kerr-nonlinear coefficient in a three-level A-type atomic system for various coupling-beam powers. The Kerr-nonlinear coefficient behaves very differently in the strong and the weak coupling power regions and changes sign when the coupling or probe frequency detuning changes sign. Comparisons of Kerr-nonlinear coefficients as functions of probe frequency detuning, coupling power, and coupling frequency detuning are presented.     

Dynamical creation of entanglement versus disentanglement in a system of three-level atoms with vacuum-induced coherences

The dynamics of entanglement between three-level atoms coupled to the common vacuum is investigated. We show that the collective effects such as collective damping, dipole-dipole interaction and the cross coupling between orthogonal dipoles, play a crucial role in the process of creation of entanglement. In particular, the additional cross coupling enhances the production of entanglement. For the specific initial states we find that the effect of delayed sudden birth of entanglement, recently invented by Ficek and Tana? [Ficek, R. Tana?, Phys. Rev. A 77 (2008) 054301] in the case of two-level atoms, can also be observed in the system. When the initial state is entangled, the process of spontaneous emission causes destruction of correlations and its disentanglement. We show that the robustness of initial entanglement against the noise can be changed by local operations performed on the state.     

Nonlinear theory of lasing with or without inversion in a simple three-level atomic system

We investigate, using a nonlinear theory of laser physics, for a simple three-level atomic system the steady-state intensity behavior due to the effects of quantum coherence and decoherence. We find that a change from a noninversion laser to an inversion laser action can occur as the Rabi frequency of the driving field increases. The steady-state intensity of the laser field can arrive at a maximal value for a certain Rabi frequency of the driving field. We also find that the linear gain and the laser intensity tend to decrease for the linewidth of the driving field.     

Controlling the optical bistability beyond the multi-photon resonance condition in a three-level closed-loop atomic system

We investigate the optical bistability behavior of a three-level closed-loop atomic system beyond the multi-photon resonance condition. Using the Floquet decomposition, we solve the time-dependent equations of motion, beyond the multi-photon resonance condition. By identifying the different scattering processes contributing to the medium response, it is shown that in general the optical bistability behavior of the system is not phase-dependent. The phase dependence is due to the scattering of the driving and coupling fields into the probe field at a frequency, which, in general, differs from the probe field frequency.     

Two-phonon process in a three-level system

The dynamical behaviour of level filling and occupation numbers of photon modes is examined rigorously. A “quantum expression” for the Rabi frequency is obtained.     

The mean first passage time of a three-level atomic optical bistable system subjected to noise

The transient properties of a three-level atomic optical bistable system in the presence of multiplicative and additive noises are investigated. The explicit expressions of the mean first-passage time (MFPT) of the transition from the high intracavity intensity state to the low one are obtained by numerical computations. The impacts of the intensities of the multiplicative noise D M and the additive noise D A , the intensity of correlation between two noises λ , and the intensity of the incident light y on the MFPT are discussed, respectively. Our results show: (i) for the case of no correlation between two noises (λ = 0.0), the increase in D M and D A can lead to an increase in the probability of the transition to the low intracavity intensity state, while the increase in y can lead to a retardation of the transition; and (ii) for the case of correlation between two noises (λ = 0.0), the increase in λ can cause an increase in the probability of the transition, and the increase in D A can cause a retardation of the transition firstly and then an increase in the probability of the transition, i.e., the noise-enhanced stability is observed for the case of correlation between two noises.     

Photon statistics and atomic dynamics in a three-level plus two-mode model

The relations between photon statistical characteristics and atomic level populations are examined rigorously. The characteristic and photon distribution functions are found.     

Generation of Raman polaritons in three-level atomic media

A theory of formation of Stokes field (Raman) polaritons, which arise due to the coherent stimulated Raman scattering of light in an ensemble of three-level atoms placed in a Fabry-Perot cavity in the case of a strong coupling regime, is developed. The dispersion and absorption properties of Raman polaritons are investigated and the conditions for polariton amplification are found. It is shown that for certain pump power values, nonclassical correlations (entanglement) between light and dark polaritons are observed in the system.     

Slow-light solitons in three-level atomic systems modified by a microwave field

We study the modified effect of slow-light soliton in a resonant three-level atomic system via electromagnetically inducedtransparency (EIT) by utilizing a microwave field. We derive ahigh-order nonlinear Schrödinger equation by using a perturbation method of multiple-scales, and calculate the modification ofsoliton velocity and frequency shift. We find that in the presence of the microwave field an obvious decrease of propagating velocityof soliton can be realized, which provides an effective method to slow down optical solitons in EIT systems. We also find that thedown shift of oscillating frequency of soliton in such system can be largely suppressed by the microwave field.     

Effects of the control field on the optical multistability in V-type three-level atomic system

The optical multistability behaviour in a ring cavity for the V-type atomic system, driven by a coherent field and control field (coherent + dc fields), has been analysed. The presence of dc field is having a dominant effect on generating the optical multistability of the system. We show that, the effects of the quantum interference from spontaneous emission and of the relative phase between the two fields of the control field might be of use to control the threshold value and width of the hysteresis cycle, which can adjust the optical switching process when they are taken at optimal values. Also, the optical multistability is predicted for the output field as a function of the cooperative parameter in the presence of the quantum interference of the spontaneous emission.