Tushar Kanti Dey

Gravitational lensing by wormholes

We have investigated the gravitational lensing by two wormholes, viz., Janis–Newman–Winnicour (JNW) wormhole and Ellis wormhole. The deflection angles in the strong field limit are calculated and various lens parameters of two wormholes are compared. It is shown that the JNW wormhole exhibits the relativistic images, while the Ellis wormhole does not have any relativistic image due to the absence of its photon sphere.

Bloch space structure, the qutrit wavefunction and atom–field entanglement in three-level systems

We have given a novel formulation of the exact solutions for the lambda, vee and cascade three-level systems where the Hamiltonian of each configuration is expressed in the SU(3) basis. The solutions are discussed from the perspective of the Bloch equation and the atom-field entanglement scenario. For the semiclassical systems, the Bloch space structure of each configuration is studied by solving the corresponding Bloch equation and it is shown that at resonance, the eight-dimensional Bloch sphere is broken up into two distinct subspaces due to the existence of a pair of quadratic constants. Because of the different structure of the Hamiltonian in the SU(3) basis, the non-linear constants are found to be distinct for different configurations. We propose a possible representation of the qutrit wave function and show its equivalence with the three-level system. Taking the bichromatic cavity modes to be in the coherent state, the amplitudes of all three quantized systems are calculated by developing an Euler angle based dressed state scheme. Finally following the Phoenix-Knight formalism, the interrelation between the atom-field entanglement and population inversion for all configurations is studied and the existence of collapses and revivals of two different types is pointed out for the equidistant cascade system in particular.

Comparison of electromagnetically induced transparency in lambda, cascade and vee three-level systems

We discuss the electromagnetically induced transparency (EIT) in lambda, cascade and vee type three-level systems where the Hamiltonian and the Lindblad term of each configuration are expressed in the representation. At steady state, the Optical Bloch Equations of each configuration are solved to obtain the dispersion and absorption profiles of the probe field along with their group velocities. When the EIT condition is achieved at resonance, the population oscillation shows which of the bare states are contributing to form the dark state. Our study reveals that the dark state for the lambda and cascade system effectively coincides with the lowest bare state of that system, while for the vee system, it is a maximally superposed state of the middle and upper bare states.

A unified approach to -, - and V-type systems with one continuum

Abstract We present a systematic approach to classify the three-level-like models with two bound states coupled to a continuum. It is shown that, when one of the discrete levels of usual three-level Lambda- (), cascade- () or Vee (V)-type systems is replaced by a continuum of states, the resulting each model can be classified into three distinct categories with nine possible configurations. We show that all these models are exactly solvable. We obtain and compare the asymmetric Fano lineshapes of the spectra for all the models. Our results are important for exploring new coherent effects in a variety of physical systems involving continuum–bound coupling such as photoassociation of cold atoms, plasmonics, quantum dots, photonic crystals, electromagnetic metamaterials and so on.

Bloch equation and atom-field entanglement scenario in three-level systems

We study the exact solution of the lambda, vee and cascade type of three‐level system with distinct Hamiltonian for each configuration expressed in the SU(3) basis. The semiclassical models are solved by solving respective Bloch equation and the existence of distinct non‐linear constants are discussed which are different for different configuration. Apart from proposing a qutrit wave function, the atom‐field entanglement is studied for the quantized three‐level systems using the Phoenix‐Knight formalism and corresponding population inversion are compared.