arXiv subjects
Publications and source records attributed to Fardin Kheirandish.
The properties of a quantum dissipative scalar field is analyzed by Caldeira-Leggett model in strong-coupling regime. The Lagrangian of the total system is canonically quantized and the full Hamiltonian is diagonalized using Fano technique. A mode-dependent probability density is introduced. The steady state energy and correlation functions at finite temperature are calculated in terms of the probability density.
In the present article the SPP propagation in an attenuating medium is investigated. The analytical calculations of the total electric-field Green's tensor of a metal-dielectric interface structure are provided and novel explicit expressions for Green's tensor of a metal-dielectric interface are presented. The contribution of plasmons are obtained by evaluating the poles of the reflection coefficient for p-polarized waves incident on the metal interface. The emission pattern of a classical dipole located above air/silver interface is studied. The relative intensity of the field to the field intensity in free space is studied for both normal and parallel orientations of the dipole. The quantum optical properties of a quantum emitter coupled to a metal surface are studied. For a quantum dot near a metal surface single photon emission is demonstrated using second-order correlation functions.
Surface plasmon polaritons scattering from 2D subwavelength silicon wires is investigated using finite difference time domain method. It is shown that coupling an incident surface plasmon polariton to inter-cavity modes of the particle can dramatically changes transmitted fields and plasmon induced forces. In particular, both transmission and optical forces are highly sensitive to the particle size that is related to the excitation of whispering gallery modes or standing-wave modes depending on the particle shape and size. This features might have potential sensing applications.
We demonstrate that a single sub-wavelength nanoaperture in a metallic thin film can be used to achieve dynamic optical trapping and control of a single dielectric nanowire. A nanoaperture can trap a nanowire, control its orientation when illuminated by a linearly-polarized incident field, and also rotate the nanowire when illuminated by a circularly-polarized incident field. Compared to other designs, this approach has the advantages of a low-power driving field entailing low heating and photodamage.
In the present article explicit expressions for the decay rate and energy level shifts of an atom in the presence of an ideal conducting wedge, two parallel plates and a half-sheet are obtained in the frame work of the canonical quantization approach. The angular and radial dependence of the decay rate for different atomic polarizations of an excited atom and also of the energy level shifts are depicted and discussed. The consistency of the present approach in some limiting cases is investigated by comparing the relevant results obtained here to the previously reported results.
Based on a microscopic approach, we propose a Lagrangian for the combined system of a rotating dielectric nanoparticle above a plane surface in the presence of electromagnetic vacuum fluctuations. In the framework of canonical quantization, the electromagnetic vacuum field is quantized in the presence of dielectric fields describing the nanoparticle and a semi-infinite dielectric with planar interface. The radiative heat power absorbed by the rotating nanoparticle is obtained and the result is in agreement with previous results when the the rotational frequency of the nanoparticle is zero or much smaller than the relaxation frequency of the dielectrics. The well known near field effect is reexamined and discussed in terms of the rotational frequency. The radiative heat power absorbed by the nanoparticle for well-known peak frequencies, is plotted in terms of the rotational frequency showing an interesting effect resembling a phase transition around a critical frequency, determined by the relaxation frequency of the dielectrics.
Starting from a Lagrangian, the electromagnetic field is quantized in the presence of a body rotating along its axis of symmetry. Response functions and fluctuation-dissipation relations are obtained. A general formula for rotational friction and power radiated by a rotating dielectric body is obtained in terms of the dyadic Green's tensor. Hamiltonian is determined and possible generalizations are discussed. As an example, the rotational friction and power radiated by a spherical dielectric in the vicinity of a semi-infinite dielectric plane is obtained and discussed in some limiting cases.
Using a minimal-coupling-scheme we investigate the quantum Brownian motion of a particle in an anisotropic-dissipative-medium under the influence of an arbitrary potential in both relativistic and non-relativistic regimes. A general quantum Langevin equation is derived and explicit expressions for quantum-noise and dynamical variables of the system are obtained. The equations of motion for the canonical variables are solved explicitly and an expression for the radiation-reaction of a charged particle in the presence of a dissipative-medium is obtained. Some examples are given to elucidate the applicability of this approach.
Recently, it was suggested that there was some sort of breakdown of quantum field theory in the presence of boundaries, manifesting itself as a torque anomaly. In particular, Fulling et al. used the finite energy-momentum-stress tensor in the presence of a perfectly conducting wedge, calculated many years ago by Deutsch and Candelas, to compute the torque on one of the wedge boundaries, where the latter was cutoff by integrating the torque density down to minimum lower radius greater than zero. They observed that that torque is not equal to the negative derivative of the energy obtained by integrating the energy density down to the same minimum radius. This motivated a calculation of the torque and energy in an annular sector obtained by the intersection of the wedge with two coaxial cylinders. In a previous paper we showed that for the analogous scalar case, which also exhibited a torque anomaly in the absence of the cylindrical boundaries, the point-split regulated torque and energy indeed exhibit an anomaly, unless the point-splitting is along the axis direction. In any case, because of curvature divergences, no unambiguous finite part can be extracted. However, that ambiguity is linear in the wedge angle; if the condition is imposed that the linear term be removed, the resulting torque and energy is finite, and exhibits no anomaly. In this paper, we demonstrate the same phenomenon takes place for the electromagnetic field, so there is no torque anomaly present here either. This is a nontrivial generalization, since the anomaly found by Fulling et al. is linear for the Dirichlet scalar case, but nonlinear for the conducting electromagnetic case.
In an attempt to understand a recently discovered torque anomaly in quantum field theory with boundaries, we calculate the Casimir energy and torque of a scalar field subject to Dirichlet boundary conditions on an annular sector defined by two coaxial cylinders intercut by two planes through the axis. In this model the particularly troublesome divergence at the cylinder axis does not appear, but new divergences associated with the curved boundaries are introduced. All the divergences associated with the volume, the surface area, the corners, and the curvature are regulated by point separation either in the direction of the axis of the cylinder or in the (Euclidean) time; the full divergence structure is isolated, and the remaining finite energy and torque are extracted. Formally, only the regulator based on axis splitting yields the expected balance between energy and torque. Because of the logarithmic curvature divergences, there is an ambiguity in the linear dependence of the energy on the wedge angle; if the terms constant and linear in this angle are removed by a process of renormalization, the expected torque-energy balance is preserved.
Based on a perturbative approach, a series expansion in susceptibility function of the medium is obtained for the Casimir force between arbitrary shaped objects immersed in a scalar or vector fluctuating field in arbitrary dimensions. Finite-temperature corrections are derived and the results are compared in first order with weak coupling regime in scattering method. The generalization to a massive vector field is also investigated.
A path-integral approach to the quantization of the electromagnetic field in a linearly amplifying magnetodielectric medium is presented. Two continua of inverted harmonic oscillators are used to describe the polarizability and magnetizability of the amplifying medium. The causal susceptibilities of the amplifying medium, with negative imaginary parts in finite frequency intervals, are identified and their relation to microscopic coupling functions are determined. By carefully relating the two-point functions of the field theory to the optical Green functions, we calculate the Casimir energy and Casimir forces for a multilayer magnetodielectric medium with both gain and loss. We point out the essential differences with a purely passive layered medium. For a single layer, we find different bounds on the Casimir force for fully amplifying and for lossy media. The force is attractive in both cases, also if the medium exhibits negative refraction. From our Lagrangian we also derive by canonical quantization the postulates of the phenomenological theory of amplifying magnetodielectrics.
Starting from a Lagrangian, electromagnetic field in the presence of a nonlinear dielectric medium is quantized using path-integral techniques and correlation functions of different fields are calculated. The susceptibilities of the nonlinear medium are obtained and their relation to coupling functions are determined. Finally, the Casimir energy and force in the presence of a nonlinear medium at finite temperature is calculated.
Based on a canonical approach and functional-integration techniques, a series expansion of Green's function of a scalar field, in the presence of a medium, is obtained. A series expansion for Lifshitz-energy, in finite-temperature, in terms of the susceptibility of the medium is derived and the whole formalism is generalized to the case of electromagnetic field in the presence of some dielectrics. A covariant formulation of the problem is presented.
In this article we investigate the Casimir effect in the presence of a medium by quantizing the Electromagnetic (EM) field in the presence of a magnetodielectric medium by using the path integral formalism. For a given medium with definite electric and magnetic susceptibilities, explicit expressions for the Casimir force are obtained which are in agree with the original Casimir force between two conducting parallel plates immersed in the quantum electromagnetic vacuum.
A canonical approach to Cherenkov radiation in the presence of a magnetodielectric medium is presented in classical, nonrelativistic and relativistic quantum regimes. The equations of motion for the canonical variables are solved explicitly for both positive and negative times. Maxwell and related constitute equations are obtained. In the large-time limit, the vector potential operator is found and expressed in terms of the medium operators. The energy loss of a charged particle, emitted in the form of radiation, in finite temperature is calculated. A Dirac equation concerning the relativistic motion of the particle in presence of the magnetodielectric medium is derived and the relativistic Cherenkov radiation at zero and finite temperature is investigated. Finally, it is shown that the Cherenkov radiation in nonrelativistic and relativistic quantum regimes, unlike its classical counterpart, introduces automatically a cutoff for higher frequencies beyond which the power of radiation emission is zero.
The entanglement dynamics of an anisotropic two-qubit Heisenberg XYZ system in the presence of intrinsic decoherence is studied. The usefulness of such system for performance of the quantum teleportation protocol ${\cal T}_0$ and entanglement teleportation protocol ${\cal T}_1$ is also investigated. The results depend on the initial conditions and the parameters of the system. For the product and maximally entangled initial states, increasing the size of spin-orbit interaction parameter $D$ amplifies the effects of dephasing and hence decreases the asymptotic entanglement and fidelity of teleportation. We show that the XY and XYZ Heisenberg systems provide a minimal resource entanglement, required for realizing efficient teleportation. Also, we find that for the some special cases there are some maximally entangled states which are immune to intrinsic decoherence. Therefore, it is possible to perform the quantum teleportation protocol ${\cal T}_0$ and the entanglement teleportation ${\cal T}_1$ with perfect quality by choosing a proper set of parameters and employing one of these maximally entangled robust states as initial state of the resource.
The effects of initial conditions and system parameters on entanglement dynamics and asymptotic entanglement for a two-qubit anisotropic XY Heisenberg system in the presence of an inhomogeneous magnetic field and spin-orbit interaction are investigated. We suppose that each qubit interacts with a separate thermal reservoir which is held in its own temperature. The effects of the parameters of the system and environment like spin-orbit interaction and temperature difference of reservoirs are also discussed.