# Roger AndrewsUniversity of the West Indies, St. Augustine | UWI · Department of Physics

Roger Andrews

PhD Physics

## About

38

Publications

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220

Citations

## Publications

Publications (38)

In this paper, the theory of the transfer efficiency of a light-harvesting system consisting of a trimer ring coupled to an acceptor site is presented. When the ring has a prepared excitation or is excited using a laser pulse, the maximum transfer efficiency is approximately 0.5, while a near-perfect transfer efficiency is generated by a single pho...

We derive and simulate the wavefunctions and double-excitation probabilities for dimer and trimer three-level systems. Perfect state transfer occurs for pulse strengths that are odd multiples of $\pi /\sqrt 2$ π / 2 when the parameter $\textit{Jt}$ Jt equals odd multiples of $\pi /2$ π / 2 and $\pi /\sqrt 2$ π / 2 for the dimer and trimer, respecti...

Introduction
No data exist on the prevalence of kidney stone disease in Trinidad and Tobago. Local clinicians have noted that the disease is very common, and this study represents the first attempt to investigate the prevalence of urolithiasis in these islands.
Objectives
The objective is to estimate the prevalence of kidney stone disease in Trinid...

We investigate two-photon transfer in a trimer of coupled three-level systems excited by laser pulses. We show that perfect state transfer and maximal entanglement are possible for certain detunings on the central site.

We analytically derive the wavefunction for the LH1-RC photosynthetic complex excited by a laser pulse. We demonstrate that the light absorption process with a resonant pulse is marginally less efficient than the single photon case.

We analyze a quantum wire that consists of a linear chain of three qutrits with nearest-neighbor interactions and detuning on the central qutrit. We derive the detuning conditions for perfect state transfer of a double excitation and for maximal entanglement between the first and third qutrits. We also analytically determine the times for perfect s...

We investigate the transfer efficiency for a LH1-RC photosynthetic complex excited by a top-hat laser pulse. We find that two laser detunings resonant with system eigenenergies produce perfect transfer efficiencies.

In the twin-island state of Trinidad and Tobago, urinary stone analysis is not routinely performed. This study investigates, via powder X-ray diffraction, 52 urinary tract calculi collected from hospitals in Trinidad. Of these, 46 stones were analysed with Rietveld refinement for quantitative analysis and materials characterization. Refined unit-ce...

The excitation probabilities, concurrence, and relative entropy of coherence for an array of three coupled two-level systems are studied analytically and numerically at various temperatures. We determine the excitation probabilities for each site, the concurrence between the outer sites, and the relative entropy of coherence of the system for three...

We investigate the effect of disorder in the laser intensity on the dynamics of dark-state polaritons in an array of 20 cavities, each containing an ensemble of four-level atoms that is described by a Bose-Hubbard Hamiltonian. We examine the evolution of the polariton number in the cavities starting from a state with either one or two polaritons in...

We investigate the effect of disorder in the laser intensity on the dynamics of dark-state polaritons in an array of 20 cavities, each containing an ensemble of four-level atoms that is described by a Bose-Hubbard Hamiltonian. We examine the evolution of the polariton number in the cavities starting from a state with either one or two polaritons in...

The effect of disorder in the intensity of the driving laser on the dynamics of a disordered three-cavity system of four-level atoms is investigated. This system can be described by a Bose-Hubbard Hamiltonian for dark-state polaritons. We examine the evolution of the first- and second-order correlation functions, the photon and atomic excitation nu...

The effect of disorder in the intensity of the driving laser on a coupled array of
cavities described by a Bose-Hubbard Hamiltonian for dark-state polaritons is
investigated. A canonically-transformed Gutzwiller wave function is used to investigate
the phase diagram and dynamics of a one-dimensional system with uniformly distributed
disorder in the...

We demonstrate control of the two-photon absorption probability for a simple three-level atom using type-I nondegenerate down-converted photons that have been phase-modulated using a spectral phase filter of variable modulation frequency and modulation depth. We find enhancement of two-photon absorption for entangled photons, as compared with that...

In this study, calibration and validation data sets from 2001 to 2005 and 2006 to 2010, respectively, were used to develop various Angström-Prescott models: A five-year model and five-year dry and wet seasonal models to calculate monthly average daily global solar radiation on a horizontal surface and twelve monthly models to estimate average daily...

We demonstrate control over the two-photon absorption of collinear type-I down-converted photons that have been phase-modulated. We find that absorption can be enhanced and suppressed using the modulation frequency and detuning parameters.

The phase diagram and dynamics of a polaritonic, laser-driven, disordered Bose-Hubbard system are investigated. We employ the site-dependent Gutzwiller method and find the Bose-glass phase and a dependence on ramp time in the dynamics.

The Keldysh formalism is used to analyze an energy-mode nonequilibrium superconductor. We find the entanglement length of the Cooper pairs contained in such a system to be of the order of 0.5x10^(-24)m.

We describe temporal control of two-photon interference of narrowband noncollinear type-I down-converted photons using symmetric spectral phase modulation. We find that the interference-fringe intensities can be controlled using the modulation depth and frequency.

We analyze the effect of atmospheric Kolmogorov turbulence on entangled orbital angular momentum states generated by parametric down-conversion. We calculate joint and signal photon detection probabilities and obtain numerically their dependence on the mode-width-to-Fried-parameter ratio. We demonstrate that entangled photons are less robust to the...

We present a general theoretical description of the temporal shaping of narrowband noncollinear type-I down-converted photons using a spectral phase filter with a symmetric phase distribution. By manipulating the spectral phase of the signal or idler photon, we demonstrate control of the correlation time and shape of the two-photon wavefunction wit...

We describe temporal shaping of narrowband noncollinear type-I down-converted photons using a symmetric spectral phase distribution. It is found that the time separation of correlated pairs exhibits an oscillatory dependence on the modulation depth.

In this paper we describe theoretically quantum control of temporal correlations of entangled photons produced by collinear type II spontaneous parametric down-conversion. We examine the effect of spectral phase modulation of the signal or idler photons arriving at a 50/50 beam splitter on the temporal shape of the entangled-photon wave packet . Th...

We have investigated theoretically the tuning characteristics of a Josephson junction within a microcavity for one-photon spontaneous emission and for one-photon and two-photon stimulated emission. For spontaneous emission, we have established the linear relationship between the magnetic induction and the voltage needed to tune the system to emit a...

We present a consistent multimode theory that describes the coupling of single photons generated by collinear Type-I parametric downconversion into single-mode optical fibers. We have calculated an analytic expression for the fiber diameter which maximizes the pair photon count rate. For a given focal length and wavelength, a lower limit of the fib...

A multimode theory describing the generation of photon pairs in a high-finesse Fabry-Perot cavity is presented. We also examine how interference of pairs produced with a local oscillator produces bunching and antibunching effects and also squeezing.

In a seminal paper devoted to rare events in quantum tunneling, F. Bardou has demonstrated that small fluctuations of potential barrier width can generate very large fluctuations of quantum electron tunneling transmission. Although for low transmission, the distribution is given by a lognormal distribution which belongs to the domain of attraction...

A multimode theory describing quantum interference of a subthreshold optical parametric oscillator (OPO) with a coherent local oscillator (LO) in a homodyne detection scheme is presented. Analytic expressions for the count rates in terms of the correlation time and relative phase difference between the LO and OPO have been derived. The spectrum of...

A microscopic multimode theory of collinear type-I spontaneous parametric downconversion in a cavity is presented. Single-mode and multimode correlation functions have been derived using fully quantized atom and electromagnetic field variables. From a first principles calculation the FWHM of the single-mode correlation function and the cavity enhan...

A theory of spontaneous parametric downconversion in a nonlinear crystal that is placed inside a microcavity in the degenerate, collinear, type I arrangement is given. Both atom and field variables are fully quantized. The photon-correlation function for the entangled photon pairs produced has a much longer correlation time (~0.4 ns) than that with...

Spontaneous parametric down-conversion is investigated theoretically for a nonlinear crystal placed inside a microcavity of length 100 microns. We find suppression and enhancement in the count rate for detectors placed outside the cavity.

Spontaneous parametric down-conversion is investigated theoretically for a nonlinear crystal placed inside a microcavity of length 100 microns. We find suppression and enhancement in the count rate for detectors placed outside the cavity

We develop a quantum theory for photon-pair correlations in Type-1 spontaneous parametric down-conversion, including crystal dispersion. We obtain different amplitudes for the correlations of degenerate (identical frequencies) and non-degenerate (different frequencies) signal and idler photons.

In this work we develop a quantum theory for fourth-order interference effects of non-degenerate (ND) and degenerate (D) photons produced in type-I spontaneous parametric down-conversion. In the first part of this work we include the effect of crystal dispersion whereby we obtain distinct amplitudes for ND and D photons. In the second part, the eff...

We present a microscopic model to describe the generation of unpolarized entangled pair photons from nonlinear crystals. A complete quantum-mechanical calculation of second-order nonlinear susceptibilities is presented. The localizability property of single photons is then discussed within the framework of the model.

A new theory for multimode parametric downconversion is given that
yields different predictions from existing treatments for photodetection
tails. The theory is rigorous and is derived from first principles. The
cases of both a single-atom and a nonlinear-crystal source are treated.
The detection is taken to be far from the source. For a single ato...

The alternative multimode theories of parametric down-conversion based on either nonlinear susceptibility models or the general quantum electrodynamic interaction are critically examined and shown not to be equivalent. The predictions can be qualitatively different; in contrast to the former, within the framework of the latter, it is necessary to d...