Quantum Control group

Quantum Control - undergraduate dissertations

Dissertations available this year

The limits of quantum-enabled optomechanical sensors

Fabrication processes developed for the semiconductor industry allow the manufacture of structures that are small enough to manifest quantum mechanical characteristics, such as quantized vibrational and rotational energies. They may be coupled to other quantum systems, ranging from individual atoms or ions to quantum dots, tiny optical cavities and superconducting resonators, allowing the construction of devices that depend for their operation upon quantum rather than classical mechanics. Optomechanical devices offer a range of detection and measurement applications, including use in gravimeters, accelerometers, gyroscopes and mass/particle sensing. Quantum phenomena provide new constraints for such devices, but also allow potential enhancements through the use of squeezing and entanglement to reduce the noise and increase the sensitivity.
This dissertation will explore the principles of quantum optomechanical systems, the range of devices that have been proposed and demonstrated, and the role of quantum mechanics in their operation, as well as the methods by which such devices may be rendered practical. It will particularly aim to establish the sensitivity limits of optomechanical sensors, and the potential use of quantum mechanical phenomena and techniques to enhance or optimize this sensitivity.

Stress analysis of a strapless evening gown

Scientific analysis and lateral thinking can bring remarkable innovations in even the most day-to-day applications, allowing revolutionary designs ranging from the use of Goretex and Lycra in technical clothing, to Howard Hughes' special cantilever constructions - recorded memorably for posterity in Hitchcock's Vertigo - for Jane Russell. This project will explore the structural requirements of fashion clothing, the constraints upon how it is tailored, and the new possibilities offered across a range of engineering applications by modern fabrics and materials from Lycra and Kevlar to laid scrim laminates.
Structures to consider would include yacht sails, hot air balloons, geodetic domes (eg Eden Project), canopies (eg Millennium Dome, Munich Olympiastadion), hammocks, suspension bridges as well as bias-cut clothing and so on. An analysis would be expected of the relevant properties of structural materials and textiles (tensile strength, (an)isotropy and elasticity; stiffness; compressibility), structural degrees of freedom and failure modes; and equations governing stress and strain in 1, 2 and 3-D would be appropriate. Extensions could cover the active control of material properties, biological analogues and biomimetic possibilities, and the potential use of strain-dependent phenomena for sensing or simply interesting cosmetic effects. The dissertation should not however be excessively extended towards complex composite materials, but remain focussed upon the engineering and applications of textiles and fabrics.

Previous dissertations

The origins and validity of the 'square law' for aircraft engines

A common rule of thumb for common aircraft piston engines is that the optimum inlet manifold pressure is proportional to the rotational speed. This dissertation will begin by exploring the origins of this rule and the physical relationships and constraints to which it corresponds; it will then explore its validity for a range of types and configurations of engines, including Diesel engines and jet turbines.
Dissertation undertaken by Charlotte Davis, 2008/9

Prospects for the optical tweezing of growing snowflakes

The growth of snowflakes - each of which seems to be unique yet symmetrical in shape - can generally be observed only under artificial conditions involving a supporting surface. Optical tweezers, using the dipole force of laser light, offer a potentially more realistic free-space environment in which to observe this fascinating process. This dissertation will explore the feasibility of optically tweezing snowflakes during their growth, and will attempt to determine the best laser wavelength, required power and optimum geometry, and estimate the extent to which the tweezing beams disturb the tweezed snowflakes.
Dissertation undertaken by Jake Radestock, 2008/9

Enhanced laser stabilization and monitoring for cold atom experiments

Studies of ultracold atoms and quantum degenerate gases almost inevitably rely upon stabilized semiconductor lasers in the production and manipulation of the ultracold species. Semiconductor lasers are electrically tunable, making them ideal for active stabilization, but they are susceptible to 'mode-hopping' between longitudinal modes of the short semiconductor cavity; and the spectroscopic stabilization is usually incapable of identifying without manual intervention the desired spectroscopic feature to which the wavelength should be stabilized. This dissertation will investigate possible modifications to conventional stabilization schemes that will allow spectral feature identification, mode-hop warning and, potentially, all-optical locking to the feature of interest.
Dissertation undertaken by Matt Proctor, 2008/9

The state of Quantum Mechanics at Christmas 1926

The theory of quantum mechanics developed at an astonishing rate in the 1920's, as recorded in a torrent of papers from some of the most famous names in physics. Some papers were truly seminal and took the subject forwards in a single bound, yet all were also based upon an already established body of physics and mathematics.
By 1926, many of the key elements of modern quantum mechanics had been established. Heisenberg had already introduced his matrix representation, and Schrödinger was about to present the wave equation that now bears his name; yet key elements, including the uncertainty principle, remained to follow. Understanding and resolving quantum mechanics was the most important challenge of the time, and the Solvay conference the following year attracted an astonishing attendance: Planck, Einstein, Dirac, de Broglie, Born, Bohr, Ehrenfest, Schrödinger, Pauli and Heisenberg were all present.
This dissertation will seek to establish the state of quantum mechanics at the end of 1926, including its experimental and mathematical origins and the specific developments achieved in that year itself.
Dissertation undertaken by Sam Fallaize, 2005/6

The momentum of light in media: the Abraham-Minkowski controversy

Two classic calculations of the momentum carried by an electromagnetic field disagree as to whether the momentum is increased or decreased by the presence of a refractive medium. This dissertation will explore the various interpretations and attempts to rationalize the two approaches, as well as recent suggestions that subtle consequences of the two theories might be experimentally observable. The project will touch upon the orbital angular momentum of light, and further manifestations of wave-particle duality.
Dissertation undertaken by Peter Bowyer, 2005
Peter's dissertation gained the highest mark in his year.

Theory and applications of acoustic levitation forces

The optical dipole force - the mechanism behind 'optical tweezers' - may be regarded as deriving from the recoil imparted when the photons of a beam of light are deflected by optical refraction. A similar force accompanies the refraction of any other momentum-carrying wave, and sound waves in air have been shown capable of levitating tungsten ball bearings. This dissertation will explore the principles underlying the acoustic levitation force, and possible applications of tailored acoustic fields from remote assembly to particle sorting.
Dissertation undertaken by Ben Snow, 2005 and Jon Burgess, 2003

Future possibilities

Quantum degenerate gases and their potential applications

The award, twice in the past ten years, of Nobel prizes for work on ultracold atoms demonstrates the excitement generated by recent developments and the importance with which physicists worldwide regard them. Most experiments in this area are still exploring the behaviour and capability of cold atomic systems and the new, quantum degenerate states of matter that they allow. Yet from every new realm of physics ultimately come technological applications. This dissertation will explore the physical mechanisms and techniques of quantum degenerate gases (Bose-Einstein condensation, Fermi gases, the Mott insulator transition, quantum vortices, etc.) and will explore the potential of these new systems for future technological applications.

Cavity-mediated optical cooling and trapping of atoms and molecules

Optical cooling and trapping techniques which exploit the force of laser light can cool atoms to within a nanoKelvin of absolute zero. These techniques, and the remarkable quantum phenomena which govern such cold systems, won the Nobel prizes in 1997 and 2001. Similar mechanisms can be used to trap and manipulate macroscopic particles, such as biological cells, using 'optical tweezers', while on a still larger scale, optical forces are responsible for the dust tails of comets and, if an impending space mission proves successful, they may soon be used to propel spacecraft using 'solar sails'.
Although molecules have so far eluded the techniques of laser cooling, several potential mechanisms have been proposed. Amongst the more promising is the use of resonant optical cavities to provide both field enhancement and the crucial dissipative mechanism that is fundamental to the cooling process. A review of the various cavity-mediated cooling and trapping schemes to have been proposed and, occasionally, investigated will make a fascinating and topical dissertation.