Coherence in parametric fluorescence

We investigate spontaneous four wave mixing (SFWM) in a single-channel side-coupled integrated spaced sequence of resonators (SCISSOR). Analytic expressions for the number of photon pairs generated, as well as the biphoton wave function (joint spectral amplitude) describing the pairs, are derived and numerically computed for different pump pulse durations and numbers of ring resonators. In the limit of a long input pump pulse, we show a strong analogy between super-linear scaling of generation efficiency with respect to the number of rings in the structure and Dicke superradiance. More generally, we discuss in detail the factors that influence the shape of the biphoton wave function, as well as the conditions for observing super-SFWM

Magnetoelectric polarizability: A microscopic perspective

We extend a field theoretic approach for the investigation of the electronic charge-current density response of crystalline systems to arbitrary applied electromagnetic fields. The approach leads to the introduction of microscopic polarization and magnetization fields, as well as free charge and current densities, the dynamics of which are described by a lattice gauge theory. The spatial averages of such quantities constitute the fields of macroscopic electrodynamics. We implement this formalism to study the orbital electronic response of a class of insulators to applied uniform dc electric and magnetic fields at zero temperature. To first-order in the applied fields, the free charge and current densities vanish; thus the response of the system is characterized by the first-order modifications to the microscopic polarization and magnetization fields. Associated with the dipole moment of the microscopic polarization (magnetization) field is a macroscopic polarization (magnetization), for which we extract various response tensors. We focus on the orbital magnetoelectric polarizability (OMP) tensor, and find the accepted expression as derived from the "modern theory of polarization and magnetization." Since our results are based on the spatial averages of microscopic fields, we can identify the distinct contributions to the OMP tensor from the perspective of this microscopic theory, and we establish the general framework in which extensions to finite frequency can be made.Comment: 24 page

From magnetoelectric response to optical activity

We apply a microscopic theory of polarization and magnetization to crystalline insulators at zero temperature and consider the orbital electronic contribution of the linear response to spatially varying, time-dependent electromagnetic fields. The charge and current density expectation values generally depend on both the microscopic polarization and magnetization fields, and on the microscopic free charge and current densities. But contributions from the latter vanish in linear response for the class of insulators we consider. Thus we need only consider the former, which can be decomposed into "site" polarization and magnetization fields, from which "site multipole moments" can be constructed. Macroscopic polarization and magnetization fields follow, and we identify the relevant contributions to them; for electromagnetic fields varying little over a lattice constant these are the electric and magnetic dipole moments per unit volume, and the electric quadrupole moment per unit volume. A description of optical activity and related magneto-optical phenomena follows from the response of these macroscopic quantities to the electromagnetic field and, while in this paper we work within the independent particle and frozen-ion approximations, both optical rotary dispersion and circular dichroism can be described with this strategy. Earlier expressions describing the magnetoelectric effect are recovered as the zero frequency limit of our more general equations. Since our site quantities are introduced with the use of Wannier functions, the site multipole moments and their macroscopic analogs are generally gauge dependent. However, the resulting macroscopic charge and current densities, together with the optical effects to which they lead, are gauge invariant, as would be physically expected.Comment: 24 pages. Minor typographical errors in Eq. 5, 14, 15 of the earlier version are correcte

Collisional decoherence reexamined

We re-derive the quantum master equation for the decoherence of a massive Brownian particle due to collisions with the lighter particles from a thermal environment. Our careful treatment avoids the occurrence of squares of Dirac delta functions. It leads to a decoherence rate which is smaller by a factor of 2 pi compared to previous findings. This result, which is in agreement with recent experiments, is confirmed by both a physical analysis of the problem and by a perturbative calculation in the weak coupling limit.Comment: 33 pages, 4 figure

The national industrial court steming of the unfair labour practice of forced resignation in Nigeria

In employment contract, the doctrine of freedom of contract prohibits forced labour. Thus, subject to the statute or terms and conditions of employment, the parties can bring the contract to an end. While the employer has the power of termination/dismissal, the employee has the right of resignation. Resignation by its nature, is intended to be voluntary, however, some employers have resorted to compelling employees to resign from their employment. This is known as forced resignation. The purpose is to get rid of the employee while creating the impression that the cessation of the employment contract was voluntary at the instance of the employee. This shambolic practice is an unfair labour practice perpetuated despite unprecedented high level of unemployment and underemployment with no measures being put in place by the government to address the monster. Forced resignation, aside being an unfair labour practice, is antithetical to security of employment with its multiple socio-economic effects. This paper adopts doctrinal methodology in examining the legal and socio-economic effects of forced resignation on employment relations in Nigeria; and analyses the strides of the National Industrial Court of Nigeria (NICN) towards stemming same, especially by banks. It is found that the NICN has declared forced resignation as wrongful/unlawful constructive dismissal, entitling the affected employee to damages. It makes vital recommendations on how to stem the ugly tides of forced resignation in Nigeria