Details of Grant 

EPSRC Reference:	EP/H051945/1
Title:	Quantum Electrodynamics for Nanotechnology
Principal Investigator:	Eberlein, Professor C
Other Investigators:
Researcher Co-Investigators:
Project Partners:
Department:	Sch of Mathematical & Physical Sciences
Organisation:	University of Sussex
Scheme:	Standard Research
Starts:	01 August 2010	Ends:	31 January 2014	Value (£):	313,210
EPSRC Research Topic Classifications:	Condensed Matter Physics Microsystems
EPSRC Industrial Sector Classifications:	No relevance to Underpinning Sectors
Related Grants:
Panel History:	Panel Date Panel Name Outcome 05 May 2010 Physical Sciences Panel- Physics Announced
Summary on Grant Application Form
Quantum theory has been extremely successful at describing the features of microscopic particles, for example the energy levels in atoms. However, in order to calculate any specific property of such a microscopic particle, one usually considers it in isolation - as if there was nothing else around in the whole world. In many cases this is justified in the sense that the impact of the rest of the world has only a very marginal effect on this microscopic particle and its properties, but there are also quite a few cases where this is not true and where the immediate vicinity of a microscopic particle radically alters the particle's properties and behaviour. Even more importantly, there are many examples in modern technology that make use of such effects and tailor the properties of a quantum system by suitably altering its environment. One prominent example are laser diodes, as used for example in CD and DVD players: these are quantum well lasers which are so much more efficient than early laser designs because the quantum well is used to force the emission of radiation into the desired lasing mode while suppressing radiation into other directions where it would be lost.This project deals with ways to alter the properties of the spin of an electron due to reflecting surfaces nearby. So far this has been investigated only in a very crude model. We want to determine how the precise material properties of surfaces, namely their frequency-dependent reflectivity and absorption of electromagnetic radiation may affect the properties of an electron spin nearby. A spin behaves like a compass needle in a magnetic field; it likes to minimize its energy by aligning itself with the field. How much energy is needed to flip a spin from one direction to the opposite depends on the spin's magnetic moment, and this and its dependence on the electromagnetic properties of materials in the vicinity is what we want to determine. Many of the ideas that people have for quantum computers involve spins that are pointing either one way or the opposite way, thus representing binary numbers 0 and 1 that form the basis of any computer. Practical designs often place such spins on or very close to a material surface. Our project will therefore contribute to finding ways of manipulating such spins in a way that is most advantageous for applications like quantum computers. Another manifestation of quantum particles interacting with material surfaces in their vicinity is the fact that they experience a drag force when moving. Such quantum friction comes about because any quantum system continuously emits and reabsorbs virtual excitations, or quantum fluctuations. If the quantum system is in motion then an imbalance is being created and not all of the excitations emitted can also be reabsorbed. Then these excitations show up as real particles, and the sum of all the momentum lost through their emission causes a frictional force opposing the motion. This usually is a very weak effect, but it increases at close distances and it may become dominant once other types of friction are removed, as is the aim in many modern micromechanical and optomechanical devices. There have been a variety of different approaches to the description of quantum friction, and there is disagreement on both the results and the theoretical methods for deriving them. All of them use purely macroscopic approaches to calculating the frictional force. We want to use our expertise to build a microscopic theory that describes the process of the emission of excitations by moving quantum systems and determine the resulting quantum friction by adding up the momentum lost by the moving object. In this way we want to show how the physical process works and which macroscopic approach is valid under which circumstances.
Key Findings
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Organisation Website:	http://www.sussex.ac.uk