About This Thesis

This, as the title indicates, is my PhD thesis. This is primarily an experimental work in which I built (or rebuilt) most of a tabletop experiment designed to study quantum mechanical phenomena using a Bose-Einstein condensate. A Bose-Einstein condensate (BEC) is a special state of matter in which all of the particles (rubidium atoms in this case) get very cold and collect in the bottom of a trap. The amazing thing is, that they're moving so slow that they become quite large (this is Heisenberg's uncertainty principle!), and begin to overlap. They overlap so much, in fact, that they can no longer be distinguished - for all intents and purposes, they are one large super-atom! The wonderful thing about this super-atom is that (a) it's large - we can see it with a camera, and (b) without a lot of thermal noise to wash things out, this super-atom will act as a quantum-mechanical, wave-like object. This is really quite magical as we can now actually watch atoms diffracting, interfering, dispersing.. all the things that were typically the realm of sound waves or light waves.

Experimental data from Chapter 5. The inset red-on-blue blob is an actual image of an expanding condensate. The traces reperesent the 1D, integrated density profile of the blob in theory (red) and in the data (blue).

The long-term ambition of the lab is to see one such wave-like phenomenon play out with atoms - quantum tunnelling. This is the odd and famous phenomenon where an object colliding with a wall has some probability of "appearing" on the other side. An important result of this thesis is the realization of the related "Muga" effect, where upon collision with a repulsive potential I have shown that atoms have some chance of mysteriously speeding up! I also present a somewhat serendipitous finding, which is that the fringes produced in these collisions can be used to reconstruct the full quantum state of the condensate before its collision.

In Chapter 1 I give a slightly more technical version of the above description, which is intended to be readable by any physicist. Chapter 2 contains a few results obtained with numerical models, making predictions beyond Muga et. al.'s original idea for momentum enhncement (i.e. quantum particles speeding up when they ought to slow down) which apply to our real system. I have shown a qualitatively different effect in a different regime, as well as a new technique that may be used to reconstruct phase and amplitude information of a quantum wavepacket. Chapter 3 details most of my technological innovations on the experiment, including a new laser system, new coils and field drivers, and updated vacuum and electronics systems. Chapter 4 gives a step-by-step description of the production of BEC, as well as a novel technique to measure and suppress momentum-space noise in the experiment. Chapter 5 provides experimental demonstrations of the effects described in Chapter 2, and Chapter 6 summarizes conclusions from the thesis.

PDF Version

Full Thesis (~6Mb)

Separated by chapter

Front Matter
Chapter 1 - Background and Motivation
Chapter 2 - Momentum Enhancement and Wavefunction Measurement
Chapter 3 - Apparatus and Technique
Chapter 4 - Experimental Cycle and BEC
Chapter 5 - Observation of Momentum Enhancement and Interference
Chapter 6 - Conclusions
Appendices and Bibliography

HTML Version

This HTML Version is automatically generated from the Latex, with a few manual adjustments. There are still a couple of typesetting issues which I'll get to eventually. For now, maybe it's easier browsing than the PDF version? I've also shaved off some of the front matter (Acknowledgements, Preface, List of Figures) for the sake of appearance.

Talk Slides

Slides for presentation (PDF)

Access Map

The department in Toronto was asking for a bound copy of my thesis so future students would have access to it. Seems a bit old-fashioned to me! Here, from my web server logs, is a map of who's looked at my thesis on my website in the past couple of months. The thesis is also available in electronic form at the U of T library. The locations are by IP address, so not always so accurate - in case you're wondering who's in the boat off West Africa. This was updated August 5th 2011.