208 research outputs found
Robust Bayesian Analysis of Loss Reserves Data Using the Generalized-t Distribution
This paper presents a Bayesian approach using Markov chain Monte Carlo methods and the generalized-t (GT) distribution to predict loss reserves for the insurance companies. Existing models and methods cannot cope with irregular and extreme claims and hence do not offer an accurate prediction of loss reserves. To develop a more robust model for irregular claims, this paper extends the conventional normal error distribution to the GT distribution which nests several heavytailed distributions including the Student-t and exponential power distributions. It is shown that the GT distribution can be expressed as a scale mixture of uniforms (SMU) distribution which facilitates model implementation and detection of outliers by using mixing parameters. Different models for the mean function, including the log-ANOVA, log-ANCOVA, state space and threshold models, are adopted to analyze real loss reserves data. Finally, the best model is selected according to the deviance information criterion (DIC).Bayesian approach; state space model; threshold model; scale mixtures of uniform distribution; device information criterion
Analysis of atomic magnetometry using metasurface optics for balanced polarimetry
Atomic magnetometry is one of the most sensitive field-measurement techniques
for biological, geo-surveying, and navigation applications. An essential
process in atomic magnetometry is measurement of optical polarization rotation
of a near-resonant beam due to its interaction with atomic spins under an
external magnetic field. In this work, we present the design and analysis of a
silicon-metasurface-based polarization beam splitter that have been tailored
for operation in a rubidium magnetometer. The metasurface polarization beam
splitter operates at a wavelength of 795 nm and has a transmission efficiency >
83% and a polarization extinction ratio > 20 dB. We show that these performance
specifications are compatible with magnetometer operation in miniaturized vapor
cells with subpicotesla-level sensitivity and discuss the prospect of realizing
compact, high-sensitivity atomic magnetometers with nanophotonic component
integration
Cluster-state creation in liquid-state NMR
Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Nuclear Science and Engineering, 2007.Includes bibliographical references (p. 57-60).The subject of this thesis is devoted to a class of multiparticle entangled states known as the cluster-states. In particular, we focused on a system of four spins and studied the entanglement properties of a four-qubit cluster-state, using a set of entanglement measures for quantifying multipartite entanglement. We then experimentally prepared the linear cluster-state in a liquid NMR sample of crotonic acid, by applying a set of pulses generated by the Gradient Ascent Pulse Engineering (GRAPE) algorithm on a temporally averaged pseudo-pure state of four carbon spins. While our spectral results were consistent with the creation of a linear cluster-state, the reconstruction of the experimental density matrix via a full state tomography of the system revealed additional challenges in the detection of certain desired spin terms. These problems must be overcome before the system could be studied quantitatively.by Jennifer T. Choy.S.B
Recommended from our members
Nanophotonic Structures for Coupling to Quantum Emitters in the Visible
This thesis is about the design, fabrication, and characterization of nanophotonic elements in the visible that can enhance light-matter interaction for single quantum emitters. We focus on two material systems: single photon sources based on the nitrogen-vacancy (NV) center in diamond with improved spontaneous emission rates and collection efficiencies, and passive TiO2 devices that comprise a potentially broadband (from the visible to the infrared), low loss photonics platform and that are suitable for probing and manipulating single colloidal quantum dots. We first discuss the requirements for using color center emission in bulk diamond crystals for potential applications in quantum information processing, and provide examples of using nanowire structures and planar resonators made in diamond for engineering the the NV center’s pump and collection efficiencies, and spontaneous emission rates, respectively. We also describe the integration of diamond with plasmonic structures. We have designed and implemented diamond-silver apertures for broadband enhancements of the spontaneous emission rates of NV centers. We show that shallow-implanted NV centers in diamond nanoposts provide a good system for controlling the NV center spontaneous emission rates, allowing for quenched emission with long lifetimes in the bare case, and enhanced emission with fast decay rates (corresponding to a Purcell factor of around 6) when coated with silver. We add plasmonic gratings around the diamond-silver apertures to improve the collection efficiency of the system, and observe over two-fold improvement in collection. We demonstrate the fabrication of chip-scale linear optical elements such as waveguides and racetrack resonators in low-loss thin films. The fabricated waveguides operate over a wide bandwidth with propagation losses from from 30 dB/cm in the visible to 4 dB/cm in the IR, while racetrack resonators can critically couple to waveg- uides and have quality factors as high as ~22000 in the red wavelengths. We present the fabrication of dielectric slot waveguides and their integration with colloidal quan- tum dots. Finally, we describe efforts to study and control charge transfer processes between quantum dots and on a single emitter level.Engineering and Applied Science
Depth dependence of the radiative lifetime of shallow color centers in single crystalline diamond
Optically active defects in diamond are widely used as bright single-photon
sources for quantum sensing, computing, and communication. For many
applications, it is useful to place the emitter close to the diamond surface,
where the radiative properties of the emitter are strongly modified by its
dielectric environment. It is well-known that the radiative power from an
electric dipole decreases as the emitter approaches an interface with a
lower-index dielectric, leading to an increase in the radiative lifetime. For
emitters in crystalline solids, modeling of this effect needs to take into
account the crystal orientation and direction of the surface cut, which can
greatly impact the emission characteristics. In this paper, we provide a
framework for analyzing the emission rates of shallow (<100 nm) defects, in
which optical transitions are derived from electric dipoles in a plane
perpendicular to their spin axis. We present our calculations for the
depth-dependent radiative lifetime for color centers in (100)-, (110)-, and
(111)-cut diamond, which can be extended to other vacancy defects in diamond
Single Color Centers Implanted in Diamond Nanostructures
The development of materials processing techniques for optical diamond
nanostructures containing a single color center is an important problem in
quantum science and technology. In this work, we present the combination of ion
implantation and top-down diamond nanofabrication in two scenarios: diamond
nanopillars and diamond nanowires. The first device consists of a 'shallow'
implant (~20nm) to generate Nitrogen-vacancy (NV) color centers near the top
surface of the diamond crystal. Individual NV centers are then isolated
mechanically by dry etching a regular array of nanopillars in the diamond
surface. Photon anti-bunching measurements indicate that a high yield (>10%) of
the devices contain a single NV center. The second device demonstrates 'deep'
(~1\mu m) implantation of individual NV centers into pre-fabricated diamond
nanowire. The high single photon flux of the nanowire geometry, combined with
the low background fluorescence of the ultrapure diamond, allows us to sustain
strong photon anti-bunching even at high pump powers.Comment: 20 pages, 7 figure
Plasmonic resonators for enhanced diamond NV- center single photon sources
We propose a novel source of non-classical light consisting of plasmonic
aperture with single-crystal diamond containing a single Nitrogen-Vacancy (NV)
color center. Theoretical calculations of optimal structures show that these
devices can simultaneously enhance optical pumping by a factor of 7,
spontaneous emission rates by Fp ~ 50 (Purcell factor), and offer collection
efficiencies up to 40%. These excitation and collection enhancements occur over
a broad range of wavelengths (~30nm), and are independently tunable with device
geometry, across the excitation (~530nm) and emission (~600-800nm) spectrum of
the NV center. Implementing this system with top-down techniques in bulk
diamond crystals will provide a scalable architecture for a myriad of diamond
NV center applications.Comment: 9 pages, 7 figure
Integrated TiO2 resonators for visible photonics
We demonstrate waveguide-coupled titanium dioxide (TiO2) racetrack resonators
with loaded quality factors of 2x10^4 for the visible wavelengths. The
structures were fabricated in sputtered TiO2 thin films on oxidized silicon
substrates using standard top-down nanofabrication techniques, and passively
probed in transmission measurements using a tunable red laser. Devices based on
this material could serve as integrated optical elements as well as passive
platforms for coupling to visible quantum emitters.Comment: 4 pages, 3 figure
- …