Experimental Background and Overview

Manuel Endres

Monika Aidelsburger

Robert John Collins, Ross J. Donaldson, Gerald S. Buller

There is ongoing research into information-theoretically secure digital signature schemes. Mathematically based approaches typically require additional resources such as anonymous broadcast and/or a trusted authority to achieve information-theoretical security. The principles of quantum mechanics can be applied to the problem to create the approach known as quantum digital signatures, which does not have these limitations. This presentation will provide an overview of the development of experimental quantum digital signatures. The evolution of experimental test-beds will be charted from small scale demonstrators to long distance implementations with commercial prototypes, along with overviews of the theoretical background of each stage.

Julien Spahn

David E. Fagnan

This thesis discusses a new technique for measuring collision cross sections, using a magnetooptical trap (MOT) or magnetic trap as well as theoretical predictions for the resulting measurements based on scattering theory. The initial discussion focuses on a theoretical overview of the principles involved in laser cooling and trapping, magnetic trapping, and scattering theory. Following this, a detailed overview of the experimental instruments and methods describing the vacuum system, laser light, magnetic coils, imaging and control systems will be presented. In addition to an experimental overview, the methods and mechanical formulation involved in predicting cross sections and loss rates based on scattering theory are discussed. Finally, an overview of both experimental and theoretical results including cross sections and loss rates for the case of trapped 87Rb and background argon or helium gas will be given. The results gathered in this thesis show a strong dependence of elastic collision cross section on trap depth, which indicates that the majority of elastic collisions between ultra-cold rubidium and room temperature argon impart energy below 1K. These results suggest that the magnetic trap may be a better tool for measuring total elastic collision cross sections.

Mark A. Reed, W. P. Kirk