<p>Shiv Nadar University is a comprehensive, multidisciplinary, research-focused, and student-centric University offering a full range of academic programs at the undergraduate, postgraduate and doctoral level. With state-of-the-art infrastructure, the University comprises of academic wings, sophisticated labs, international standard sports facilities, amphitheaters, auditorium, conference rooms and smart classrooms. The University&rsquo;s goal is to become internationally recognized for the quality of its research and creative endeavors and their applicability to improving quality of life, generating new insights and expanding the boundaries of human knowledge creativity. Committed to excellence in teaching, research and service, the University aims to serve the higher education needs of India and the world beyond.</p>

Shiv Nadar University

We probe the propagation of short electromagnetic pulses of finite bandwidth through a one-dimensional nonlinear photonic crystal. The theoretical scheme is tested in numerical simulations of the reflection and transmission spectra for a sample of recent experimental interest. The study is important for understanding of the nonlinear phase shifts and other active spectral modifications in photonic crystals, which have potential applications in all-optical signal processing. © 2006 Optical Society of America.

World University root node

SNU Management

Journal of the Optical Society of America B: Optical Physics

Reflection and transmission spectra for ultrashort pulse propagation in a one-dimensional nonlinear photonic crystal

Starting from the field master equation for a laser oscillating simultaneously in two modes, we probe the dependence of its fundamental phase-diffusion linewidth on the degree of coupling between the two modes. We find that the heterodyned intrinsic linewidth shows the usual decrease when the output power of each mode increases with an increase in the gain, while the nonlinear self-saturation and cross-coupling coefficients are held constant. The linewidth also decreases with increase in the cross-coupling between the modes for constant gain when the output power of each mode is kept constant by decreasing the self-saturation coefficient. The linewidth, however, increases with increasing cross-coupling when (a) the gain and the self-saturation coefficient are held constant and hence the output power in each mode decreases and (b) the gain is increased keeping the output power and the self-saturation of each mode constant.

Journal of Optics B: Quantum and Semiclassical Optics

Theory of the fundamental linewidth of a two-mode laser

We consider the general problem of a single two-level atom interacting with a multimode radiation field (without the rotating-wave approximation), and additionally take the field to be coupled to a thermal reservoir. Using the method of bosonization of the spin operators in the Hamiltonian, and working in the Bargmann representation for all the boson operators, we obtain the propagator for the composite system using the techniques of functional integration, under a reasonable approximation scheme. The propagator is explicitly evaluated for a simplified version of the system with one spin and a dynamically coupled single-mode field. The results are also checked on the known problem of quantum Brownian motion.

Journal of Physics A: Mathematical and General

Propagator for a spin-Bose system with the Bose field coupled to a reservoir of harmonic oscillators

The quantum Brownian motion (QBM) with couplings nonlinear (quadratic) in the environment coordinates was studied. The influence functional for nonlinear interactions up to second order of perturbation with generalized initial conditions was constructed. This functional was used to get the propagator for the particle in a harmonic potential as well as for the particle in an additional an harmonic potential.

Physical Review E - Statistical, Nonlinear, and Soft Matter Physics

General quantum brownian motion with initially correlated and nonlinearly coupled environment

The dynamics of an open quantum system exhibiting the quantum Brownian motion is analyzed when the coupling between the system and its environment is nonlinear, and the system and the reservoir are initially correlated. For couplings quadratic in the environment variables, the influence functional for the system is obtained perturbatively up to second order in the coupling constant, and then the propagator is explicitly evaluated when the particle is under the influence of a harmonic potential and an additional anharmonic potential, the so-called washboard potential. As an application of the propagator, the master equation and the Wigner equation are obtained for the quantum Brownian particle moving in a harmonic potential for the generalized correlated initial condition, and then for the specific case of the simplified “thermal” initial condition. The system is shown to obey the corresponding fluctuation-dissipation theorem. © 2003 The American Physical Society.

Physical Review E - Statistical Physics, Plasmas, Fluids, and Related Interdisciplinary Topics

General quantum Brownian motion with initially correlated and nonlinearly coupled environment

Magnetochiral anisotropy refers to the phenomenon that when light is passed through a chiral medium placed in an external magnetic field, the refractive index, or equivalently, the absorption encountered by the light differs depending on whether it travels parallel or antiparallel to the magnetic field. It is a very small effect, the change in refractive index because of this effect alone being of the order of 10-11. This effect has recently been measured in an active ring laser interferometer in which the detection scheme convincingly eliminates the contributions from natural optical activity, the Faraday effect and other stray anisotropies in the system. The phenomenon is important in the context of fundamental interactions between light and matter and the governing symmetry principles, and also in biochemistry as one possible explanation for the homochirality of life.

Pramana - Journal of Physics

Probing magnetochirality

Fulltext

Erratum: Probing magnetochirality (Pramana - Journal of Physics 59:2 (189-194))

Pramana - Journal of Physics: Preface

A complete analysis of the magneto-optic drift effects of optically active ions, incorporating buffer-induced collision mechanisms within the Markov limit was carried out. It was shown that a combination of the cyclotron motion of charged active atoms in an applied coaxial magnetic field and the usual light-induced drift due to velocity-changing collisions with a buffer gas yields an effective way to confine the optical piston action to a one-dimensional motion.

Physical Review A. Atomic, Molecular, and Optical Physics

Magneto-optic drift of ions

Light-induced drift of optically active atoms in a buffer gas is a consequence of the unequal diffusive frictions suffered by the excited and the ground-state atoms. This drift can be used to create an “optical piston", in which the active atoms are pushed forward by light through the semipermeable membrane of the buffer gas. Normally, optical piston effect is studied when the active atoms are neutral in a confined one-dimensional situation. We present a detailed theory of this phenomenon when the active atoms are charged and a magnetic field is applied for “tuning” the direction as well as the magnitude of the drift, thus removing the necessity of confinement. Our study is in different geometries of the light beam and the magnetic field, first in the weak collision model, and then for the strong collision and the Boltzmann-Lorentz models. © 2001 The American Physical Society.

Physical Review A - Atomic, Molecular, and Optical Physics

Magnetochiral birefringence observed in a ring laser configuration for two chiral compounds was studied. True magnetochiral variation of the refractive index was isolated independent of the associated polarization effects. The change in refractive index in limonene was found to be 10-10 at 488 nm with a magnetic field of 1.3KG.

Physical Review Letters

Observation of magnetochiral birefringence

In this study, an attempt was made to solve the dynamics of the Stern-Gerlach spin in contact with a linearly dissipative environment at an arbitrary temperature. All the previous results in the high-temperature limit were recovered. It was observed that except for the extreme quantum case of zero temperature, the system shows the expected classical diffusive behavior over long times.

Quantum theory of a Stern-Gerlach system in contact with a linearly dissipative environment

Drift of optically active atoms in a buffer gas induced by an incident light field is a consequence of the unequal diffusive frictions suffered by the excited and the ground-state atoms. We investigate this light-induced drift in the presence of a magnetic field in a direction perpendicular to the incident light, which gives rise to an interesting effect, appropriately called the "optical Hall effect.".

Optical Hall effect

We present the quantum theory of a Stern-Gerlach system in contact with a linearly dissipative environment at an arbitrary temperature. The dynamics of the reduced density matrix of the system is calculated using the path integral technique, under a general condition when the system and its environment may not be decoupled initially. We analyze the behavior of the density matrix in the long-time limit and compute the time scales of decay of the elements off-diagonal in the coordinate and the momentum space, for the cases of high temperature, zero temperature, and intermediate temperature baths. © 2000 The American Physical Society.

Drift of optically active atoms in a buffer gas induced by an incident light field is a consequence of the unequal diffusive frictions suffered by the excited and the ground-state atoms. We investigate this light-induced drift in the presence of a magnetic field in a direction perpendicular to the incident light, which gives rise to an interesting effect, appropriately called the “optical Hall effect.” © 2000 The American Physical Society.

Light-induced drift of optically active atoms in a buffer gas is a consequence of the unequal diffusive frictions suffered by the excited and the ground-state atoms. This drift can be used to create an “optical piston,” which is best observed when the piston action is confined to a one-dimensional motion. We show that a novel way of realizing this phenomenon is to apply a magnetic field on charged active atoms. © 1999 The American Physical Society.

Magneto-optic piston effect

In many nonlinear optical problems, for example in down-conversion and four-wave mixing, the photons are generated in pairs. The strong correlation between the photons in a pair, characterized by either the correlations between operators corresponding to observables associated with individual photons, or the correlated state describing the two photons, may lead to various nonclassicalities. We discuss some of these nonclassical effects and their experimental demonstrations in nonlinear optical processes.

Quantum correlations in optics

A dynamical model for the collapse of the wave function in a quantum measurement process is proposed by considering the interaction of a quantum system (spin - 1 2) with a macroscopic quantum apparatus interacting with an environment in a dissipative manner. The dissipative interaction leads to decoherence in the superposition states of the apparatus, making its behaviour classical in the sense that the density matrix becomes diagonal with time. Since the apparatus is also interacting with the system, the probabilities of the diagonal density matrix are determined by the state vector of the system. We consider a Stern-Gerlach type model, where a spin- 1 2 particle is in an inhomogeneous magnetic field, the whole set up being in contact with a large environment. Here we find that the density matrix of the combined system and apparatus becomes diagonal and the momentum of the particle becomes correlated with a spin operator, selected by the choice of the system-apparatus interaction. This allows for a measurement of spin via a momentum measurement on the particle with associated probabilities in accordance with quantum principles. © 1995.

Physica A: Statistical Mechanics and its Applications

Environment-induced decoherence I. The Stern-Gerlach measurement

According to Bell's theorem, the degree of correlation between spatially separated measurements on a quantum system is limited by certain inequalities if one assumes the condition of locality. Quantum mechanics predicts that this limit can be exceeded, making it nonlocal. We analyse the effect of an environment modelled by a fluctuating magnetic field on the quantum correlations in an EPR singlet as seen in the Bell inequality. We show that in an EPR setup, the system goes from the usual 'violation' of Bell's inequality to a 'non-violation' for times larger than a characteristic time scale which is related to the parameters of the fluctuating field. We also look at these inequalities as a function of the spatial separation between the EPR pair. © 1995.

Environment-induced decoherence II. Effect of decoherence on Bell's inequality for an EPR pair

Optical tests of the quantum Zeno effect [W.M. Itano et al., Phys. Rev. A 41 (1990) 2295] are analyzed using the environment-induced decoherence theory, where the spontaneous emission lifetime of the relevant level emerges as the "decoherence time". The implication of this finite decoherence time in setting a fundamental limit on the realizability of continuous measurements is investigated in detail. © 1995.