arXiv subjects

Fazal Ghafoor

Publications and source records attributed to Fazal Ghafoor.

9 recordsLinked to original sources

arXiv2017

Control of Fano resonances and slow light using Bose-Einstein condensates in a nanocavity

In this study, a standing wave in an optical nanocavity with Bose-Einstein condensate (BEC) constitutes a one-dimensional optical lattice potential in the presence of a finite two bodies atomic interaction. We report that the interaction of a BEC with a standing field in an optical cavity coherently evolves to exhibit Fano resonances in the output field at the probe frequency. The behavior of the reported resonance shows an excellent compatibility with the original formulation of asymmetric resonance as discovered by Fano [U. Fano, Phys. Rev. 124, 1866 (1961)]. Based on our analytical and numerical results, we find that the Fano resonances and subsequently electromagnetically induced transparency of the probe pulse can be controlled through the intensity of the cavity standing wave field and the strength of the atom-atom interaction in the BEC. In addition, enhancement of the slow light effect by the strength of the atom-atom interaction and its robustness against the condensate fluctuations are realizable using presently available technology.

quant-ph↗

arXiv2015

Multiple electromagnetically induced transparency, slow and fast light in hybrid optomechanics

We theoretically investigate the phenomenon of electromagnetically induced transparency (EIT) of a weak probe field in hybrid optomechanics with a single three-level ($Λ$-type) atomic system. We report that, in the presence of optomechanical coupling and two transition coupling parameters of three-level atom (TLA), there occurs three distinct multiple EIT windows in the probe absorption spectrum. Moreover, the switching of multiple windows into double and single EIT windows can be obtained by suitably tuning the system parameters. Furthermore, the probe transmission spectrum have been studied. Based on our analytical and numerical work, we explain the occurrence of slow and fast light (superluminal) regimes, and enhancement of superluminal behaviour in the probe field transmission. This work demonstrates great potential in multi-channel waveguide, fiber optics and classical communication networks, multi-channel quantum information processing, real quality imaging, cloaking devices and delay lines & optical buffers for telecommunication.

quant-ph↗

arXiv2015

Electromagnetically induced transparency and tunable fano resonances in hybrid optomechanics

We explain the phenomena of electromagnetically induced transparency (EIT) of a weak probe field and tunable Fano resonances in hybrid optomechanics. The system of study consists of a two-level atom coupled to a single-mode field of an optomechanical resonator with a moving mirror. We show that a single EIT window exists in the presence of optomechanical coupling or Jaynes-Cummings coupling, whereas two distinct double EIT windows occur when both the couplings are simultaneously present. Furthermore, based on our analytic and numerical work, we prove the existence of tunable fano resonances in the system. The controlling parameters of the system, which switch from a single EIT window to double EIT windows and are needed to tune the fano resonances, can be realized in present-day laboratory experiments.

quant-ph↗

arXiv2014

Slow and fast light dynamics in a chiral cold and hot atomic medium

We study Chiral Based Electromagnetically Induced Transparency (CBEIT) of a light pulse and its associated subluminal and superluminal behavior through a cold and a hot medium of 4-level \textit{double-Lambda type} atomic system. The dynamical behavior of this chiral based system is temperature dependent. The magnetic field based chirality and dispersion is always opposite as compared with the electric field ones. Contrastingly, the response of the chiral effect along with the incoherence Doppler broadening mechanism enhances the superluminal behavior as compared with its traditional degrading effect. Nevertheless, the intensity of a coupled microwave field destroys the coherence of the medium and degrade superluminality and subluminality of the sysmtem. The undistorted retrieved pulse from a hot chiral medium delays by $896 ns$ than from a cold chiral medium under same set of parameters. Nevertheless, it advances by $-31n s$ in the cold chiral medium when a suitably different spectroscopic parameters are selected. The corresponding group index of the medium and the time delay/advance, are studied and analyzed explicitly [Note: A revise version is under preparation

quant-ph↗

arXiv2013

Hole-burning in an Autler-Townes doublet and in superluminal (subluminal) Electromagnetically induced transparency of a light pulse via a joint nonlinear coherent Kerr effect and Doppler broadening

We investigate the behavior of light pulse propagation in a 4-level double Lambda atomic system under condition of electromagnetically induced transparency. The Fano type interference effect and spectral hole burning appears in the the dynamics of the absorption-dispersion spectra caused by the joint nonlinear coherence Kerr effect and Doppler broadening. The coherent Kerr effect exhibits an enhancement (reduction) in superluminal (subluminal) in negative (in positive) group index while the Doppler broadening generates multiple hole burning in the Autler-Townes like spectra of this system. The hole burning in addition with coherent Kerr effect on the spectral profile influences the dynamics of subluminal and superluminal of the probe pulse through the medium. The characteristics of superluminality and subluminality modified by considering cold-Kerr-free medium and hot-Kerr-dependent mediums. The light pulse delays and advances in different regions of dispersion medium with the Doppler broadening and coherent Kerr effect. Consequently, the pulse delays by $49μs$, while advance by $-91μs$, for a same set of parameters [note: a revised version is under preparation

physics.optics↗

arXiv2013

Avoidance of instability of a superluminal Gaussian light pulse via control of nonlinear coherence Kerr effect in a gain-assisted medium

We investigate nonlinear Kerr-induced coherence effect on a superluminal probing light pulse in a gain-assisted N-type 4-level atomic system via an intense monochromatic laser field. The dispersion exhibits a novel, interesting and useful two-paired double gain lines processes. The system displays lossless characteristics similar to [L. J. Wang, A. Kuzmich, A. Dogariu, Nature \textbf{406}, 277 (2000)] but with advantages of \emph{multiple} \textbf{controllable} anomalous regions, \emph{significantly enhanced} superluminal behavior and \textbf{relaxed} temperature, states of matter regardless of its isotropic or anisotropic conditions. Unlike the instability in [A. M. Akulshin, S. Barreiro, and A. Lezama, Phys. Rev. Lett. \textbf{82}, 4277 (1999)], the present system also \emph{overcomes the instable-limit} by the Kerr-induced coherence effect in the system. Indeed, the coherence enhances the group velocity remarkably by at least $-30 ms$ more than of an instable Kerr-free system with almost negligible distortion in the retrieved pulse.

physics.optics↗

arXiv2013

Superluminal light propagation in a bi-chromatically Raman-driven and Doppler-broadened N-type 4-level atomic system

We investigate the behavior of fast light pulse propagation in an N-type Doppler-broadened 4-level atomic system using double Raman gain processes. This system displays novel and interesting results of two controllable pairs of the double gain lines profile with a control field. The detailed physics of the processes are explored having multiple controllable anomalous regions in the medium. In this set up, the system exhibits significant enhancement in the probing Gaussian pulse through the medium as compared with Ref. [L. J. Wang, A. Kuzmich, and A. Dogariu, Nature \textbf{406}, 227(2000)]. The advance time of the retrieved Gaussian pulse is always greater than the advance time studied in the above said experiment. We analyzed that the pulse propagating through the medium with larger negative group index, $7.32\times10^8$, leaves the medium almost undistorted and sooner by time $76.12 \ ms$ than the pulse which leaves the medium of Wang \emph{et al.}. The Gaussian pulse always remains almost undistorted at output due to lossless characteristic of the medium. We also underlined the ways to suppress incoherences generated by the Doppler-broadening effect in the system. The limitations of the recently developed applications require to explore mechanisms for ultimate speed of a superluminal probe light pulse. In this connection, the proposed scheme may be helpful and can be easily adjusted with the current technology.

physics.optics↗

arXiv2013

An alternative realization of spontaneous emission cancelation via Field Generated Coherence (FGC)

In contrast to the traditional Spontaneous Generated Coherence (SGC), Field Generated Coherence (FGC)-based atomic scheme is presented for spontaneous emission cancellation. It is easy to achieve externally controllable experimental trapping condition in this 4-field-driven 5-level atomic system. Consequently, due to the FGC the decay from the central dressed \emph{bare-energy-state} of the set of upper three closely spaced hyperfine decaying states of Sodium D2 line is completely cancelled under the trapping condition, exhibiting a novel phenomenon of a \textit{dark bare-energy-state}% . Extending to an atomic system of simple probability loss, based on Sodium D1 line, the bright atom can also be darkened under its trapping condition, representing another experimentally viable, novel and interesting phenomenon.

quant-ph↗

arXiv2013

Autler-Townes multiplet spectroscopy

We extend the concepts of the Autler-Townes doublet and triplet spectroscopy to quartuplet, quintuplet and suggest linkages in sodium atom in which to display these spectra. We explore the involved fundamental processes of quantum interference of the corresponding spectroscopy by examining the Laplace transform of the corresponding state-vector subjected to steady coherent illumination in the rotating wave approximation and Weisskopf-Wigner treatment of spontaneous emission as a simplest probability loss. In the quartuplet, four fields interact appropriately and resonantly with the five-level atom. The spectral profile of the single decaying level, upon interaction with three other levels, splits into four destructively interfering dressed states generating three dark lines in the spectrum. These dark lines divide the spectrum into four spectral components (bright lines) whose widths are effectively controlled by the relative strength of the laser fields and the relative width of the single decaying level. We also extend the idea to the higher-ordered multiplet spectroscopy by increasing the number of energy levels of the atomic system, the number of laser fields to couple with the required states. The apparent disadvantage of these schemes is the successive increase in the number of laser fields required for the strongly interactive atomic states in the complex atomic systems. However, these complexities are naturally inherited and are the beauties of these atomic systems. They provide the foundations for the basic mechanisms of the quantum interference involved in the higher-ordered multiplet spectroscopy.

quant-ph↗