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Physica Scripta

Generation of optical -antisymmetry in a coherent N-type atomic medium

Bibhas Kumar Dutta, Pradipta Panchadhyayee

Published Apr 6, 2023• 2 citations
Publisher

Abstract

Abstract We have proposed two schemes to exhibit   -antisymmetry in a four-level N-type atomic system interacting with two strong driving fields and a weak probe field. For both the schemes, the required spatially modulated coherence rendering   -antisymmetry is achieved by employing a double-channel Gaussian beam for one driving field with a single channel for the other driving field in different field configurations. In each scheme, for equal and opposite detunings of the double-channel Gaussian beam,   -antisymmetry can be obtained in the spatial domain. Such a way of control is unique to this model. Using the present method, it is possible to obtain   -antisymmetry for both the homogeneously and inhomogeneously broadened atoms.

DOI
10.1088/1402-4896/accb18

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Journal of the Arkansas Academy of Science•Jan 1, 2012•0 citations
Abstract We have proposed two schemes to exhibit   -antisymmetry in a four-level N-type atomic system interacting with two strong driving fields and a weak probe field. For both the schemes, the required spatially modulated coherence rendering   -antisymmetry is achieved by employing a double-channel Gaussian beam for one driving field with a single channel for the other driving field in different field configurations. In each scheme, for equal and opposite detunings of the double-channel Gaussian beam,   -antisymmetry can be obtained in the spatial domain. Such a way of control is unique to this model. Using the present method, it is possible to obtain   -antisymmetry for both the homogeneously and inhomogeneously broadened atoms.
A collection of cold rubidium atoms in three-level configuration trapped in two dimensional (2D) optical lattices is revisited. The trapped atoms are considered in the Gaussian density distribution and we study the realization of P T -, non- P T -, and P T -antisymmetry in 2D optical lattices. Such a fascinating modulation is achieved by spatially modulating the intensity of the driving field. Interestingly, control over P T - to non- P T -symmetry and vice versa in 2D optical lattices is achieved via a single knob such as microwave field, probe field and relative phase of optical and microwave fields. In addition, control over P T -antisymmetry to non- P T -symmetry and vice versa is also achieved via relative phase. The coherent control of P T - non- P T - and P T -antisymmetry in optical susceptibility of 2D atomic lattices can be extended to 2D optical devices including modulators, detectors, and the 2D atomic lattices can also be extended to photonic transistors and diodes.
Abstract We propose a physical scheme to realize optical lattices that are symmetric under a combination of parity and time ( ) reversal. The -symmetric structures can be constructed with periodical gain and loss profiles in a coherently prepared four-level N-type atomic system under the effects of cross-Kerr nonlinearity and Doppler broadening. The atoms are considered in the Gaussian density distribution loaded into the dipole traps of one- and two-dimensional optical lattices. The spatial modulation of the probe field susceptibility is achieved by a proper combination of standing wave strong control fields. With proper detunings and coupling field Rabi frequencies, we find the conditions of achieving -symmetry in optical lattices of nonlinear atoms. We show that the -symmetry can be realized when the cross-Kerr nonlinearity is significantly enhanced, and further demonstrate that it survives the Doppler broadening. Our model is based on experimentally observable and effectively controllable scheme which may find potential applications in optical information processing.
We study an ensemble of ultracold atoms trapped in the one-dimensional optical lattices under the N level configuration to examine the absorption and dispersion properties modulated into different ways along the lattice direction z. We find these trapped atoms with a Gaussian density distribution in each period may exhibit either symmetry χp(z)=χp*(-z) or antisymmetry χp(z)=-χp*(-z) of parity-time (PT) in terms of the probe susceptibility. Such intriguing twofold modulations of real (χ'p) and imaginary (χ″p) susceptibilities with a π/2 phase shift are attained by spatially modulating intensities or frequencies of one driving field in a suitable way. The PT-symmetric or PT-antisymmetric atomic lattices correspond in fact to complex photonic crystals and may be extended to develop functional devices like photonic diodes and transistors, a task impossible for real photonic crystals.
We have studied nonlinear quantum optical effects in a doubly driven four-level atomic system in a homogeneously broadened regime. On application of two strong fields the system can be made to display double electromagnetically induced transparency (EIT) because of constructive quantum interference giving rise to nonlinear absorption at three-photon resonance condition. This fact may be used to obtain other phenomena like the effect of photon switching in a pulsed regime and large cross phase modulation (XPM) effect. We also show that the behaviour of spatial modulation of transparency of the weak probe beam in a three-level system interacted with a strong standing wave pump field can be dramatically changed in our four-level ladder type system. Here, strong coupling field acting on the uppermost transition is represented by a standing wave whereas strong pump and weak probe fields acting successively on the lower transitions are represented by travelling waves. The effect of double EIT on nonlinear light generation based on the four-wave-mixing (FWM) technique is also investigated. We have examined that the four wave mixing efficiency can be effectively controlled by varying the strength of the pump field.
Abstract We have studied two-dimensional absorption, gain, and corresponding refractive index profiles in a ladder-type three-level atomic system interacting with three coherent fields. One is a weak probe field considered as a plane wave, while the other two are the control fields taken as two Laguerre–Gaussian doughnut beams. Position dependence of two vortex beams induces the spatially modulated coherence at the condition of resonance, which enables us to obtain space-dependent absorption, transparency, gain without inversion (GWI), and refractive index enhancement in the present scheme. The azimuthal modulation of coherence effects is attributed to the presence of optical angular momentum of the vortex beams. Under the influence of an additional travelling wave field with the presence of two vortex beams, the present model leads us to obtain an ultra-large enhancement of refractive index at the resonant detuning of the fields. This phenomenon makes the atom-field system to play the equivalent role of a high-refractive-index prism. The role of near dipole–dipole (NDD) interaction on the modulation of position-dependent coherence effects has also been investigated. It has been shown that, without any inclusion of the travelling wave field in the system, the phenomenon of resonant enhancement of refractive index may also occur in the presence of NDD effect. The new way of generating spatially controlled GWI and nonlinear refractive index enhancement is specific to the present model. This work seems to be useful for finding its applications in spatially modulated coherence controlled electromagnetically induced transparency-based quantum devices like quantum optical memory, switches, and quantum logic gates, where the refractive index switching phenomenon is a prerequisite.
In this thesis, atomic coherence is used to enhance nonlinear optical processes in multi-level atoms. The multi-photon transitions are driven resonantly, and at the same time without absorptive losses, by using electromagnetically induced transparency (EIT), thereby allowing the study of χ(3) and χ(5) nonlinearities using weak driving fields. The coherently modified probe beam(s) and the atom-radiated signal fields arising from four- and six- wave- mixing (FWM and SWM) processes are measured in the spectral, temporal and spatial domains. In a three-level ladder-type atomic system, multiple peaks having spectral asymmetries are observed in the EIT window as well as in the FWM signal waveforms due to the diverse multiplicities of the participating atomic states. Using phase control tailored in the frequency domain, we demonstrate all-optical methods to control these spectral waveforms and discuss applications involving waveform-shaping and metrology. For the EIT study we demonstrate a switching of multiple dark peaks into bright peaks via phase-control of interferences in the underlying dark-states. In the FWM study we demonstrate all-optical spectral line shape symmetrization, linewidth narrowing and bandwidth switching. In a four-level inverted-Y-type atomic system, we drive and measure coexisting and phase-matched FWM and SWM signals. By using precision control of the relative phase and amplitude between these two processes of different nonlinear orders, we demonstrate phase coherence between them. First, a single-phase measurement is performed in the temporal and spatial domains, and the interferogram is used to measure the resonant frequency of the 5D5/2-5P3/2 atomic transition in 85Rb. Second, the method is extended to realize a capacity for two-phase measurement. In this case, the spectral bandwidth of the signal is modified in order to measure the phase-shift occurring in one Mach-Zehnder interferometer, while the intensity of the total signal waveform measures the phase-shift occurring in a second interferometer. Finally, we demonstrate phase-dependent spatial fusion between two ultra-weak optical fields by using a strong coupling field to first convert the weak fields into bosonic dark-state polaritons, which are then steered into a common all-optical waveguide mode arising due to the coupling field's intensity distribution and the resulting cross-Kerr refractive index gradient.