Acknowledgements

I would like to gratefully acknowledge the enthusiastic supervision of Dr. Stefano Giorgini and Prof. Lev P. Pitaevskii. They taught me so many new things and were always ready to answer any of my countless questions.

I owe special thanks to Prof. Sandro Stringari without whom this Dissertation would not exist. I want to thank him for giving me the opportunity to work in his group, for being a great mentor, for giving me invaluable help in solving the organizational problems.

I am grateful to the many people I have met in the Trento BEC group, in the University of Trento and who have assisted me so much in the course of this work.