Bandwidth of linearized electrooptic modulators

Many schemes have been proposed to make high dynamic range analog radio frequency (RF) photonic links by linearizing the transfer function of the link's modulator. This paper studies the degrading effects of finite transit time and optical and electrical velocity dispersion on such linearization schemes. It further demonstrates that much of the lost dynamic range in some modulators may be regained by segmenting and rephasing the RF transmission line

A lead sulfide near infrared detection system

The infrared region of the spectrum is conveniently divided into the near infrared, which extends from the red end of the visible to about 25 microns, and the far infrared, which continues to an ill-defined division point of approximately 1,000 microns. The near infrared region has been further subdivided on the basis of instrumental techniques so that the particular portion of the spectrum consisting of radiations of wave length up to 3 microns has become known as the photoelectric infrared. Several types of detection instruments have been designed and perfected for work in the photoelectric region, but new methods and materials are constantly being sought which might give an increase in sensitivity and contribute to the simplicity of the system. Recently developed lead sulfide photoconductive cells have some of the characteristics desired. These cells respond over a region in the spectrum from about .5 micron to 3.5 microns and their high sensitivity offers the possibility of greatly increased resolving power over previous methods used. Their subminiature size is also a highly desirable physical trait in almost all cases. Some writers, who have engaged in early research on photoconductive materials, have stated that lead sulfide and similar materials have opened up a wide new field in spectroscopy. As a result of these advantages, infrared detectors utilizing them are beginning to make an appearance. A detector using a PbS cell and designed so that it would be readily adaptable to a standard spectrometer should be or great assistance in furthering the study of the near infrared. Such a device could be used advantageously in the classroom and laboratory when familiarization with and research into the longer electromagnetic radiations is desired. With this particular type of system in mind, design and construction of the photoconductive infrared detector was attempted. To check the dependability of the completed PbS system, it was proposed to use it in extending from the visible into the near infrared region, the dispersion curve of an ordinary glass prism --Introduction, pages 1-2

Dispersal Dynamics in a Wind-Driven Benthic System

Bedload and water column traps were used with simultaneous wind and water velocity measurements to study postlarval macrofaunal dispersal dynamics in Manukau Harbour, New Zealand. A 12-fold range in mean wind condition resulted in large differences in water flow (12-fold), sediment flux (285-fold), and trap collection of total number of individuals (95-fold), number of the dominant infaunal organism (84-fold for the bivalve Macomona liliana), and number of species (4-fold). There were very strong, positive relationships among wind condition, water velocity, sediment flux, and postlarval dispersal, especially in the bedload. Local density in the ambient sediment was not a good predictor of dispersal. Results indicate that postlarval dispersal may influence benthic abundance pat- terns over a range of spatial scales

The Accuracy of Perturbative Master Equations

We consider open quantum systems with dynamics described by master equations that have perturbative expansions in the system-environment interaction. We show that, contrary to intuition, full-time solutions of order-2n accuracy require an order-(2n+2) master equation. We give two examples of such inaccuracies in the solutions to an order-2n master equation: order-2n inaccuracies in the steady state of the system and order-2n positivity violations, and we show how these arise in a specific example for which exact solutions are available. This result has a wide-ranging impact on the validity of coupling (or friction) sensitive results derived from second-order convolutionless, Nakajima-Zwanzig, Redfield, and Born-Markov master equations.Comment: 6 pages, 0 figures; v2 updated references; v3 updated references, extension to full-time and nonlocal regime

Effects of Velocity Mismatch and Transit Time on Linearized Electro-Optic Modulators

The program written for this study allows calculations for periodically-rephased modulators since the modulator is already broken up into a series of incremental matrices. Thus if the modulator is allowed to be mismatched for a few matrices and then rephased for the next few and so on, we have the results shown for a four segment modulator (3 rephasings). modulators are considered

Direct excitation of the forbidden clock transition in neutral 174Yb atoms confined to an optical lattice

We report direct single-laser excitation of the strictly forbidden (6s^2)^1S_0 -(6s6p)^3P_0 clock transition in the even 174Yb isotope confined to a 1D optical lattice. A small (~1.2 mT) static magnetic field was used to induce a nonzero electric dipole transition probability between the clock states at 578.42 nm. Narrow resonance linewidths of 20 Hz (FHWM) with high contrast were observed, demonstrating a record neutral-atom resonance quality factor of 2.6x10^13. The previously unknown ac Stark shift-canceling (magic) wavelength was determined to be 759.35+/-0.02 nm. This method for using the metrologically superior even isotope can be easily implemented in current Yb and Sr lattice clocks, and can create new clock possibilities in other alkaline earth-like atoms such as Mg and Ca.Comment: Submitted to Physics Review Letter

Analytical model of non-Markovian decoherence in donor-based charge quantum bits

We develop an analytical model for describing the dynamics of a donor-based charge quantum bit (qubit). As a result, the quantum decoherence of the qubit is analytically obtained and shown to reveal non-Markovian features: The decoherence rate varies with time and even attains negative values, generating a non-exponential decay of the electronic coherence and a later recoherence. The resulting coherence time is inversely proportional to the temperature, thus leading to low decoherence below a material dependent characteristic temperature.Comment: 19 pages, 3 figure