Elias J. Griffith

Ideal Gas Behavior of a Strongly Coupled Complex (Dusty) Plasma

In a laboratory, a two-dimensional complex (dusty) plasma consists of a low-density ionized gas containing a confined suspension of Yukawa-coupled plastic microspheres. For an initial crystal-like form, we report ideal gas behavior in this strongly coupled system during shock-wave experiments. This evidence supports the use of the ideal gas law as the equation of state for soft crystals such as those formed by dusty plasmas.

Rapid-state purification protocols for a Cooper pair box

We propose techniques for implementing two different rapid state purification schemes, within the constraints present in a superconducting charge qubit system. Both schemes use a continuous measurement of charge (z) measurements, and seek to minimize the time required to purify the conditional state. Our methods are designed to make the purification process relatively insensitive to rotations about the x-axis, due to the Josephson tunnelling Hamiltonian. The first proposed method, based on the scheme of Jacobs [Phys. Rev. A 67, 030301(R) (2003)] uses the measurement results to control bias (z) pulses so as to rotate the Bloch vector onto the x-axis of the Bloch sphere. The second proposed method, based on the scheme of Wiseman and Ralph [New J. Phys. 8, 90 (2006)] uses a simple feedback protocol which tightly rotates the Bloch vector about an axis almost parallel with the measurement axis. We compare the performance of these and other techniques by a number of different measures.

Guidance and control in a Josephson charge qubit

In this paper we propose a control strategy based on a classical guidance law and consider its use for an example system: a Josephson charge qubit. We demonstrate how the guidance law can be used to attain a desired qubit state using the standard qubit control fields.

Spectroscopy of a Cooper-Pair box in the Autler-Townes configuration

A theoretical spectroscopic analysis of a microwave driven superconducting charge qubit (Cooper-pair box coupled) to an RLC oscillator model is performed. By treating the oscillator as a probe through the backreaction effect of the qubit on the oscillator circuit, we extract frequency splitting features analogous to the Autler-Townes effect from quantum optics, thereby extending the analogies between superconducting and quantum optical phenomenology. These features are found in a frequency band that avoids the need for high frequency measurement systems and therefore may be of use in qubit characterization and coupling schemes. In addition we find this frequency band can be adjusted to suit an experimental frequency regime by changing the oscillator frequency.

Target tracking for missile warning applications

Traditional missile warning systems (MWSs) have tended to use the ultra-violet waveband, where the ambient intensity levels tend to be low and the resultant false alarm rate is comparatively small. The development of modern infrared imagers has generated interest in the use of infrared imagers in MWSs. Infrared cameras can detect the heat signatures of missile plumes, which peak in the mid-wave (3-5 micron) infrared band, but they can also contain appreciable levels of noise: including intermittent defects that are of the same size as the potential targets. Typically, both missiles and defects will only occupy a few pixels in each image. This paper reviews a project concerned with developing an MWS algorithm toolbox for use in evaluating infrared MWSs. In particular, the paper discusses some of the main problems associated with detecting and tracking missiles in infrared imagery from a moving platform in the presence of localised image noise.

Equivalence of BRISK Descriptors for the Registration of Variable Bit-Depth Aerial Imagery

Using low bit depth images for image processing applications offers a number of advantages over full depth images, reduced data transmission, removal of superfluous detail and improved compressibility with potential reduction in FPGA resource usage for use on-board small UAS platforms. It is demonstrated here that Binary Robust Invariant Scalable Key point (BRISK) descriptors can often be matched directly, without modification, between images with differing number of gray levels (bit-depth). The performance is evaluated within the context of obtaining a sufficient number of control points for an image registration problem. This could be used to determine direct equivalence of an unknown, unaligned, reduced palette image against a known reference image of superior bit-depth.

Binary Data Embedding Framework for Multiclass Classification

This paper proposes a novel manifold embedding method for the automated processing of large varied datasets. The method is based on binary classification, where the embeddings are constructed so as to determine one or more unique features for each class individually from a given dataset. The proposed method is applied to examples of multiclass classification that are relevant for large-scale data processing for surveillance (e.g., face recognition), where the aim is to augment decision making by reducing extremely large sets of data to a manageable level before displaying the selected subset of data to a human operator. The method consists of two stages: Preprocessing and embedding computation. In the embedding computation, adaptive measures of intraclass and interclass information are proposed, based on the concepts of “friend closeness” and “enemy dispersion.” In addition, an indicator for weighted pairwise constraint is proposed to balance the contributions from different classes to the final optimization, in order to better control the relative positions between the important data samples from either the same class (intraclass) or different classes (interclass). The effectiveness of the proposed method is evaluated through comparison with seven existing techniques for embedding learning, using four established databases of faces, consisting of various poses, lighting conditions, and facial expressions, as well as two standard text datasets. The proposed method performs better than these existing techniques, especially for cases with small sets of training data samples.

Characterizing a superconducting charge qubit via environmental noise

In this paper, we propose a technique to characterise the energy level structure of a superconducting charge qubit. The technique relies on the backreaction of a solid-state qubit on its environment and the incoherent transfer of energy from a high frequency mode to a low frequency mode due to the stochastic transitions of the qubit between energy eigenstates. We consider a coupled system consisting of a model charge qubit and several classical degrees of freedom. The qubit is coupled to three electromagnetic modes: a low frequency bias field, a higher frequency mode (which is used to pump the qubit from the ground state to an excited state), and a lossy reservoir (which represents the cavity that contains the qubit and control fields). The reservoir provides a mechanism to allow the qubit to dissipate energy and to induce spontaneous decays from an excited state into the ground state. We show that these spontaneous decays can have a significant effect on the noise in the classical bias field, and that this noise can be used to characterise the energy level structure of the qubit.

Nonlinear kinematics for improved helicopter tracking

This paper compares the tracking performance that can be achieved when using a nonlinear drag model for a helicopter, a constant drag motion model, and a baseline constant acceleration model. A particle filter is used for state estimation to address problems associated with nonlinear drag and nonlinear measurements of helicopter pose. We demonstrate that the inclusion of this nonlinear kinematic effect provides improved tracking performance for a manoeuvring target.

Doing the Right Thing: Collision Avoidance for Autonomous Air Vehicles

Collision Avoidance is a critical requirement in Aviation safety. Unmanned Aircraft Systems (UASs) are required to adhere to Rules of the Air, outlined in the UK by the Civil Aviation Authority (CAA), and to be able to resolve any potential collision situations. This work investigates rules governing two common situations; converging traffic, and head-on approach. This paper considers the implementation of a generic flight planner using simulated UAS models. Upon detection of a potential collision, an appropriate collision avoidance maneuver is calculated and executed, with the aircraft reverting to their desired path afterwards.