How Does a Bose-Einstein Condensate Develop Phase?

The demonstration of Bose-Einstein Condensation in 1995 was a major milestone in physics. When atoms are extremely cold, their de Broglie wavelengths can overlap, forming a single macroscopic quantum fluid with well defined phase. Theorists have long pondered the origins of this phase. In this experimental program we aim to answer for the first time the intriguing question: "How does a BEC develop phase?". The answer will also be important for the recently developed atom laser - with potential applications as wide-reaching as the laser - where understanding the phase coherence is important for devices such as atom interferometers.