inverted-Y System Research Articles

Influence of Doppler broadening on cross-Kerr nonlinearity in a four-level inverted-Y system: An analytical approach

In this work, we study the influence of Doppler broadening on cross-Kerr nonlinearity in a four-level inverted-Y atomic system under electromagnetically induced transparency (EIT) condition. The first- and third-susceptibilities in the presence of Doppler effect are derived as a function of probe, signal and coupling beams and temperature of medium. Under EIT condition, cross-Kerr nonlinearity is enhanced several orders of magnitude compared to that without EIT. The Doppler effect leads to a reduction in the transparent efficiency and thus reduces the amplitude of cross-Kerr nonlinear coefficient. For hot atomic gaseous medium, such consideration of the Doppler effect may be useful for experimental observations and apply to photonic devices operating at different temperature conditions.

Spectral characteristics of a modified inverted-Y system beyond rotating wave approximation

The spectral properties of a multilevel atomic system interacting with multiple electromagnetic fields, a modified inverted-Y system, have been theoretically investigated. In this study, a numerical matrix propagation method has been employed to study the spectral characteristics beyond the validity regime of the rotating wave approximations. The studied atomic system, comprising of several basic sub-systems, i.e. lambda, ladder, vee, N and inverted-Y, is useful to study the interdependence among these basic sub-systems. The key features of the obtained probe spectra as a function of coupling strength and detuning of the associated electromagnetic fields show inter-conversion, splitting and shifting of the transparency and absorption peaks. The dressed and doubly dressed state formalism have been utilized to explain the numerically obtained results. This study has application in design of novel optical devices capable of multi-channel optical communication along with switching.

Sub-luminal and super-luminal light propagation in inverted-Y system with wavelength mismatching effects

We investigate the electromagnetically induced transparency phenomenon in a four-level inverted-Y system, i.e. composite of three-level Λ and Ξ systems, using the density matrix formalism theoretically in stationary as well as moving atoms. Most of the EIT studies have taken the probe and coupling fields with wavelength matched condition to minimize the effect of Doppler-broadening. In this work we show a variation of absorption and dispersion profiles with wavelength mismatching factor because in real atoms for multilevel system the matched wavelength condition is difficult to obtain. This mismatching results in Doppler-broadening. We show that for moving atoms at the room temperature, a narrow window is also present within the wide transparency window for the probe absorption and dispersion for the mismatched cases. The group index modifies the probe propagation from super-luminal to sub-luminal within a very small detuning range near resonance. The variation of the group index with the coupling fields shows optical switching behavior when one of the coupling field is slightly detuned.

Revisiting the four-level inverted-Y system under both Doppler-free and Doppler-broadened conditions: an analytical approach

We report the occurrence of electromagnetically induced transparency (EIT) in the simulated probe response signal for a four-level inverted-Y type system that is being acted upon by a weak coherent probe field, a strong coherent pump field and a coherent repump field. There are two ground energy levels, one intermediate energy level and one uppermost energy level. The weak probe field couples the lowest ground level to the intermediate level whereas the repump field connects the other ground level with the intermediate level. The strong control field couples the intermediate level with the uppermost energy level, thereby forming an inverted-Y type system. The density matrix based theoretical model has been developed and solved analytically for this four-level system and the probe response signal has been simulated at different values of the control and repump Rabi frequencies, control and repump frequency detunings and under both Doppler-free and Doppler-broadened conditions using the parameters of 87Rb D2 transition. Extremely low line width (few tens of kHz) for the EIT signal has been noticed under thermal averaging for copropagating probe, control and repump field configuration. The EIT signal is found to be immune to the variation in the control Rabi frequency.

Phase-dependent high refractive index without absorption in a four-level inverted-Y atomic system

We consider a closed four-level inverted-Y system in the presence and the absence of a microwave field. It is found that due to the quantum coherence between the two lower levels, either induced by the spontaneous decay or by the microwave field, the refraction – absorption properties of the system can be modulated by controlling the relative phase of the applied fields in both driven ways. In particular, by properly setting the values of the relative phase, the desirable high index of refraction without absorption can be achieved.

Two-Dimensional Atom Localization via Spontaneous Emission in an Inverted-Y System

We investigate the behavior of two-dimensional atom localization in an inverted-Y system driven by one coherent field and two standing-wave fields. The position probability distribution of the atom passing through the spatial-position-dependent standing-wave fields can be determined by measuring the spontaneously emitted photon. It is found that high-precision two-dimensional atom localization can be obtained by choosing appropriate system parameters.

Two-dimensional atom localization via quantum interference in a coherently driven inverted-Y system

A scheme for two-dimensional (2D) subwavelength atom localization is proposed, in which the atom is in an inverted-Y configuration and driven by two orthogonal standing-wave lasers. Due to the spatial dependence of atom–field interaction, the quantities of system, including the frequency of spontaneously emitted photon, the population in the excited state, and the probe absorption, carry information about the position of atom in standing-wave fields. We exploit this fact to 2D atom localization, and obtain a high precision and resolution in the position probability distribution.

Propagation of twin light pulses under magneto-optical switching operations in a four-level inverted-Y atomic medium

Propagation dynamics of twin laser pulses through a cold four-level inverted-Y atomic medium is investigated theoretically via switching on and off an external magnetic field under the application of a strong driving field. By numerically solving the coupled Bloch–Maxwell equations for atom and field simultaneously on a spacetime grid, our spatio-temporal results clearly show that dynamic control of twin-pulse propagation and magneto-optic dual switching operation are possible in such an inverted-Y system. The proposed scheme may be used for the design of magneto-optic switching and magneto-optic storage devices.

Ultra-slow soliton pairs in four-level inverted Y-system via electromagnetically induced transparency

Using the Schrödinger Maxwell equations, we theoretically investigate the propagation properties of probe and mixing fields in a lifetime-broadened inverted-Y type cold atomic medium. This system is driven by two strong control (pumping and coupling) fields. The results reveal that the probe (or mixing) field consists of two modes with different group velocity and absorption. Under slowly varying envelope approximation, we discuss the propagation equation of the probe (or mixing) field, which includes the high-order nonlinear term. The solutions show that optical solitons pairs can be generated in the cold atom medium with ultra-slow group velocities.

Effect of spontaneously generated coherence on EIT and its refractive properties in four- and five-levels systems

The effects of spontaneously generated coherence (SGC) and phases of optical fields on the phenomenon of electromagnetically induced transparency (EIT) are investigated in a four-level inverted-Y system and in a five-level K-type system under various parametric conditions in order to demonstrate controllability of the EIT, dispersion properties, and group velocity in such systems. Non-zero second-order susceptibility in both systems is due to the SGC effect. The experimental viability of the model in semiconductor quantum well systems is also discussed.

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.

Nonclassical light generation via a four-level inverted-Y system

We have theoretically analyzed nonclassical paired photons generated spontaneously from a four-level inverted-Y atomic system. We discuss the feasibility of biphoton generation due to different pumping arrangements. Two types of correlated photon pair emissions have been carefully examined: dressed cascade and dressed double- emissions. In the dressed cascade two-photon emission, the coincidence counting rate may exhibit a damped Rabi oscillation, in contrast with a simple exponential decay feature in the literatures. In the dressed double- configuration, we show that not only is the temporal correlation of entangled Stokes‐antiStokes photons in agreement with discussions presented by Wen et al. Phys. Rev. A 76, 013825 2007, but also the oscillation period may be manipulated by altering either the control Rabi frequency or the dressing Rabi frequency or both. All the observed damped Rabi oscillations in the two-photon coincidences result from the destructive interference among the possible four-wave mixing processes occurring in the atom-field interaction system. This feature of the two-photon amplitude is governed by the convolution between the phase matching and third-order nonlinear susceptibility. The methodology adopted here can be applied to other atomic-level configurations and provides a useful tool to study the spectroscopy of the system. The generated narrow-band photon pairs may have potential applications in long-distance quantum communication and quantum information processing.

Phase gate with a four-level inverted-Y system

The four-level atomic system in an inverted-Y configuration is investigated for large Kerr nonlinearities. The cross-Kerr nonlinearity generated in such a system can produce a phase shift of order $\ensuremath{\pi}$ and can be used for realizing polarization quantum phase gates.