Phase standard for Bose-Einstein condensates

We discuss how a consistent phase standard for Bose-Einstein condensates may be defined. We show that it has the properties we would wish for in a phase standard: it is not corrupted by subsequent comparisons. A quantum jump technique is employed to study the time evolution of a three mode condensate system on which we make measurements, which entangle the modes and so establish relative phases between them. By establishing, in turn, the phases of two condensates relative to a reference condensate, we show that the relative phase between them can be predicted accurately. The existence of such a phase standard gives a precise definition to the phase of a condensate. [S0031-9007(99)08970-X].