HOW DOES A BEC DEVELOP PHASE?

Theoretical physicists are unsure how a condensate develops phase.  The underlying question is whether the relative phase of two condensates is created by spontaneously broken symmetry or by some other mechanisms.  It has been suggested, and studied in great detail by several authors, that such a relative phase can be created by individual atom detection where it is not known from which BEC the detected atom came.  This measurement induced phase, is a consequence of the Von Neuman projection postulate of quantum theory, and gives rise to a definite relative phase between two condensates even if the initial states of the condensates are of undefined phase.

Answering the Question:

In this experimental program we propose measuring the development of relative phase between two BEC’s.  To do this, we plan to design and construct a state-of-the-art He* BEC which has the unique characteristic that we will use a double well potential to create independent condensates. We intend to output couple atoms from two independent condensates and detect their arrival position and arrival time on a detector located below.  Interference fringes in the spatial distribution of detected atoms indicate a definite relative phase between the condensates.  Moreover, by monitoring the evolution of these fringes as a function of time we will be able to follow the evolution of condensate phase. Most importantly, by counting individual atoms, with high temporal and spatial resolution, we will be able to observe the transition from no fringes to fringes, (i.e. from no relative phase to the onset of relative phase).  In so doing we will be able to answer the question “How does a BEC develop phase?”