Physics and Technology of small Josephson junctions

The recent interest in developing highly controllable quantum bits (qubits) based on superconducting circuits makes it necessary to get a deeper understanding of the physics of small Josephson junctions. Such devices have to be wisely engineered and well isolated from the noisy environment to observe non-classical physics. In this thesis, a real-time noise analysis was implemented by an autocorrelation calculation to identify the type of environmental effects affecting a superconducting circuit. This was used during switching current measurements of small Josephson junctions to track the effects of unwanted signals and identify their frequency components. The temperature dependence of the switching current distribution was used to further characterise the small Josephson junctions. Furthermore the fabrication of smal1 Josephson junctions is further developed by analysing the reliability and reproducibility of them. A systematic approach is shown to solve typical fabrication problems for example identifying and reducing mechanical stress between resist layers. As Josephson junctions show quantum mechanical effects on a macroscopic scale they are used in a wide range of applications especially in superconducting circuits.EThOS - Electronic Theses Online ServiceGBUnited Kingdo

A Search for Gravitational Radiation from PSR 1937+214

A search for gravitational radiation from the "millisecond pulsar", PSR 1937+214, using a 40 meter baseline laser interferometric detector is described. Four days of observation yielded 1.2 x 105 seconds of data. Throughout the experiment, the pulsar phase was synthesized to an accuracy of better than one tenth of the pulsar period. A trigger generated from this signal synchronized the data averaging. Narrow band amplitude spectra centered at the pulsar's fundamental electromagnetic pulsation frequency (~642 Hz) and its first harmonic were obtained. The spectra, one for each combination of polarization and center frequency, place 99.7% confidence level limits on the emitted gravitational radiation. In dimensionless strain, h, the rms limits are: 642 Hz "plus" polarization 1.6 x 10-17 " "cross" " 3.1 x 10-17 1294 Hz "plus" polarization 1.1 x 10-17 " "cross" " 1.5 x 10-17 Over the four day observing period, the performance of the detector varied with changing temperature. During the stable night hours, the two optical cavities remained locked to reflection minima for 20 to 80 minutes before momentarily losing lock. Temperature changes of 1° to 2°C in the morning and evening necessitated compensating adjustments to the optics to maintain good fringe visibility. The interferometer senses changes in the separations between three test masses. The test masses hang like pendulums so that they are free to move in response to gravitational radiation. The suspension system is designed to provide passive isolation from seismic and environmental vibration noise. The orientation of each test mass is stabilized with a feedback loop. The design of the test masses, their suspension systems, and the servo system which controls their orientation is described.</p

Characterization and Improvement of Thrust Balance Measurement Technique for SX3 Applied-Field Magnetoplasmadynamic Thruster

Steady state applied-field magnetoplasmadynamic thruster promises good compromise between thrust density and specific impulse, making them relevant for interplanetary missions requiring high thrusts. The IRS 100 kW gas-fed steady-state AF-MPD SX3 thruster has shown promising results in previous held test campaigns. Experimental results in those campaigns showed non-linear behavior of tare forces, resulting in respective error in the thrust measurement and this error then propagates in further calculation of Isp, thrust efficiency, etc. This motivated improvement in the thrust balance and measurement technique. Various error sources in the thrust measurement technique were identified and solutions to mitigate them were presented. A number of changes in the thrust balance were made in order to improve the measurement technique and data quality. The effectiveness of improvements had been experimentally characterized and presented. Previously the thrust measurement technique featured manual control of the measurement setup which led to complex and inconsistent test procedures. A new programmable electronic control unit was specifically designed for more consistent and automated measurement and calibration procedure. Potential error sources of the measurement chain have been systematically identified, characterized and discussed. The analysis tool for thrust characterization was redesigned which gives fine control of the interval selection and data export, this ensured accurate thrust and calibration calculations. The new code is more modular to adapt for changes and is very flexible with user interaction reducing complexity while still retaining the functionality. To further improve the measurements accuracy some suggestions are made.Outgoin

System dynamics approach to user independence in high speed AFM

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2010.Cataloged from PDF version of thesis.Includes bibliographical references (p. 135-146).As progress in molecular biology and nanotechnology continues, demand for rapid and high quality image acquisition has increased to the point where the limitations of atomic force microscopes (AFM) become impediments to further discovery. Many biological processes of interest occur on time scales faster than the observation capability of conventional AFMs, which are typically limited to imaging rates on the order of minutes. Imaging at faster scan rates excite resonances in the mechanical scanner that can distort the image, thereby preventing higher speed imaging. Although traditional robust feedforward controllers and input shaping have proven effective at minimizing the influence of scanner distortions, the lack of direct measurement and use of model-based controllers has required disassembling the microscope to access lateral motion with external sensors in order to perform a full system identification experiment, which places excessive demands on routine microscope operators. This work represents a new way to characterize the lateral scanner dynamics without addition of lateral sensors, and shape the commanded input signals in such a way that disturbing dynamics are not excited in an automatic and user-independent manner. Scanner coupling between the lateral and out-of-plane directions is exploited and used to build a minimal model of the scanner that is also sufficient to describe the source of the disturbances. This model informs the design of an online input shaper used to suppress components of the high speed command signals. The method presented is distinct from alternate approaches in that neither an information-complete system identification experiment, nor microscope modification are required. This approach has enabled an increase in the scan rates of unmodified commercial AFMs from 1-4 lines/second to over 100 lines/second and has been successfully applied to a custom-built high speed AFM, unlocking scan rates of over 1,600 lines/second. Images from this high speed AFM have been taken at more than 10 frames/second. Additionally, bulky optical components for sensing cantilever deflection and low bandwidth actuators constrain the AFM's potential observations, and the increasing instrument complexity requires operators skilled in optical alignment and controller tuning. Recent progress in MEMS fabrication has allowed the development of a new type of AFM cantilever with an integrated sensor and actuator. Such a fully instrumented cantilever enables direct measurement and actuation of the cantilever motion and interaction with the sample, eliminating the need for microscope operators to align the bulky optical components. This technology is expected to not only allow for high speed imaging but also the miniaturization of AFMs and expand their use to new experimental environments. Based on the complexity of these integrated MEMS devices, a thorough understanding of their behavior and a specialized controls approach is needed to guide non-expert users in their operation and extract high performance. The intrinsic properties of such MEMS cantilevers are investigated, and a combined approach is developed for sensing and control, optimized for high speed detection and actuation.by Daniel J. Burns.Ph.D

39th Aerospace Mechanisms Symposium

The Aerospace Mechanisms Symposium (AMS) provides a unique forum for those active in the design, production, and use of aerospace mechanisms. A major focus is the reporting of problems and solutions associated with the development and flight certification of new mechanisms. Organized by the Mechanisms Education Association, NASA Marshall Space Flight Center (MSFC) and Lockheed Martin Space Systems Company (LMSSC) share the responsibility for hosting the AMS. Now in its 39th symposium, the AMS continues to be well attended, attracting participants from both the United States and abroad. The 39th AMS was held in Huntsville, Alabama, May 7-9, 2008. During these 3 days, 34 papers were presented. Topics included gimbals and positioning mechanisms, tribology, actuators, deployment mechanisms, release mechanisms, and sensors. Hardware displays during the supplier exhibit gave attendees an opportunity to meet with developers of current and future mechanism components

In Situ Tribochemical Characterization of Nanolubricants

Lubrication plays important roles in mechanical systems in motion. The challenge in understanding the characteristics of a lubricant under working conditions lies in its dynamic nature, and it is impossible to observe the target directly. The objective of this thesis research is to obtain better fundamental understanding of nanolubricants under shear. Specifically, a methodology that enables in situ detection of a rubbing pair is developed. Using this approach, the properties and performance of nanoluricants are studied. The resulting tribochemical products as tribofilms are investigated. This research consists investigation in three aspects. The first is to develop in situ triboelectrochemical techniques enabling basic study. An integrated tribotesting system combined a disc-on-disc tribotesting with electrochemical impedance measurement. The second is to study the properties of working lubricants, their electrical and thermal properties. The electrical conductivity against the oil film thickness was examined. Results showed the non-ohmic behavior of a lubricating film in the hydrodynamic regime. Properties of lubricants and testing conditions are some of the factors affecting the conductivity. The study on thermal performance over a mineral oil and polyalphaolefin (PAO) were carried out. Results showed that thermal properties of lubricants depended on the shear and they were not constants as being known. This research revealed the potential existence of dynamic properties of a working lubricant. The third is to investigate tribochemical interactions between nanolubricants and rubbing surfaces of a substrate. Using α-ZrP nanoparticles as additives, a nanolubricant produced a tribofilm with consistent electrical properties that reduced friction for 40% and wear 90%. Research results showed that under shear, a tribofilm consisting of pyrophosphate

Spectral Analysis and Parameter Estimation in Fibre Levitated Optomechanics

In levitated optomechanics, nano-scale objects are optically trapped so that their motion can be studied. These trapped nanoparticles are held in a 3D quadratic potential and act as damped harmonic oscillators; they are thermally and mechanically decoupled from the apparatus and their position is measured interfer-ometrically to picometre accuracy. These systems are well suited to sensing and metrology applications, as any external disturbance of the particle can be observed using the scattered trapping light.When examining the motion of a levitated nanoparticle, it’s position is recorded and used to estimate a power spectral density (PSD), from which state parameters can be estimated. In this thesis an experi-mental setup is presented, optimised for maximum collection of particle position information in 1D, using a fibre-based parabolic mirror trap and heterodyne measurement system in order to produce spectra with minimal noise and unwanted artefacts.A novel application of the Middleton expansion from RF engineering is used to generate a complete power spectrum that depends on the physical parameters of the system. This method treats the particle as a stochastic harmonic oscillator, phase modulated by a Gaussian random process with known PSD. We reproduce the PSD of intensity at a detector, a quantity that is sinusoidally dependent on particle posi-tion. This technique generates a single, full PSD using modified Bessel functions, and does not depend on assumptions about the relative phases of the interfered fields, highlighting the non-linear dependence of measured signal on position. Theoretical spectra are fitted to a measured PSD and the phase modulation depth is extracted; this is used to calculate the particle oscillation amplitude and, by an equipartition ar-gument, the centre of mass temperature to mass ratio. State parameters are tracked as environmental conditions change and an increase in centre of mass temperature as a function of decreasing background gas pressure is observed

Evolution of entanglement structure in open quantum systems

The thesis presents research related to the dynamics of quantum systems, both isolated and in the presence of interactions with their environment. Generally, I employ matrix product state (MPS) techniques to explore quantum dynamics in open and closed systems. In the first part I present a study of quantum chaos and how mapping to a MPS variational manifold allow the use of techniques developed in the study of classical many-body systems. Using code developed for this project the Lyapunov spectrum is extracted to give an alternative perspective on eigenstate thermalization, pre-thermalization and integrability. In the second part, I present a novel combination of MPS methods with a Langevin description of the open system. I use this to show how coupling to the environment restricts the growth of entanglement. The consequences of this are relevant for simulations of open quantum systems and their use in in quantum technologies. Finally I discuss applications of these ideas to quantum search. I consider adiabatic and quantum walk algorithms for optimal scaling quantum search algorithms, and hybridizations between the two. The robustness of the different underlying physical mechanisms is investigated in a simple infinite-temperature model, and in a low-temperature limit using the MPS Langevin equation