Fazal Ghafoor

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 analytical 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.

Gain assisted multiple surperluminal regions via a Kerr nonlinearity in a double lambda-type atomic configuration

A four level double lambda-type atomic configuration is extended to polychromatic pump fields driven from the ground to the same excited hyperfine sublevel. Multiple superluminal regions are observed in the gain peak regions and between the two pairs of gain peak regions. Furthermore, the effect of cross Kerr nonlinearity is introduced in the system by applying an additional driving field. Large enhancement in the superluminality is observed as compared to the previously observed superluminality without the Kerr nonlinearity. The results clearly show a small negative group velocity of ? 0.72?m?s?1 with a negative time delay of ?42.2?ms in the presence of the Kerr field. In this connection, useful theoretical techniques are presented for the enhancement of slow and fast light propagation. This generalized model is adjustable with the current applied technologies of cloaking devices and spacial mode images.

Linear and nonlinear optical response of MgxZn1−xO: A density functional study

Abstract Total and partial density of states, frequency dependent complex refractive index including extinction coefficient, optical conductivity and transmission of MgxZn1−xO (0≤x≤1) in rocksalt and wurtzite phases are calculated using full potential linearized augmented plane wave (FP-LAPW) method. The real part of refractive index decreases while the extinction coefficient, optical conductivity and transmission for rocksalt phase increases with the increase in Mg concentration. In wurtzite phase, ordinary and extraordinary indices decrease while extinction coefficient, optical conductivity and transmission increase in parallel as well as perpendicular to c-axis with the increase in the Mg concentration.

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.

Autler?Townes multiplet spectroscopy

The Autler?Townes doublet and triplet spectroscopy are well known in the literature. Here, atomic systems for quartuplet, quintuplet emission spectroscopy and their linkages with the sodium atom are investigated for display of the corresponding spectra. We explore the involved fundamental processes of quantum interference in these systems 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 (quintuplet), four (five) fields interact appropriately and resonantly with the five-level (six-level) atom. The spectral profile of the single decaying level, upon interaction with three (four) other levels, splits into four (five) destructively interfering dressed states generating three (four) dark lines in the spectrum. These dark lines divide the spectrum into four (five) spectral components (bright lines) whose widths are effectively controlled by the relative strength of the laser fields and the relative width of a single decaying level. The idea is also extended to higher-ordered spectroscopy. The apparent disadvantage of these schemes is the successive increase in the number of laser fields required for the strongly interactive atomic states. However, these complexities are naturally inherited and are the beauty of these atomic systems. They provide the foundations for the basic mechanisms of the quantum interference involved in the higher-ordered multiplet spectroscopy.

Triplet absorption spectroscopy and electromagnetically induced transparency

Coherence phenomena in a four-level atomic system, cyclically driven by three coherent fields, are investigated thoroughly at zero and weak magnetic fields. Each strongly interacting atomic state is converted to a triplet due to a dynamical Stark effect. Two dark lines with a Fano-like profile arise in the triplet absorption spectrum with anomalous dispersions. We provide conditions to control the widths of the transparency windows by means of the relative phase of the driving fields and the intensity of the microwave field, which closes the optical system loop. The effect of Doppler broadening on the results of the triplet absorption spectroscopy is analysed in detail.