Abstract

In quantum trajectory theory [1] the quantum state of a photoemissive source satisfies a stochastic, pure state evolution that is conditioned on the history of photocounts recorded by an imagined spherical detector centered on the source. The detector may be divided into individual elements to provide a history of emission angles as well as emission times. When the source is an extended atomic sample, it has been usual for the spherical detector construction to be applied to each atom; hence, the quantum trajectory algorithm is implemented with quantum jumps for individual atoms, as is suggested by the independent-atom radiative damping terms that appear in the corresponding master equation. This implementation is appropriate for inter-atomic separations that are much larger than the optical wavelength. In this case, the imagined detection of the emitted radiation may image the atoms separately, making the quantum jumps for individual atoms operationally well defined. At smaller separations, separate imaging of the atoms is no longer possible. Then quantum trajectory theory must be implemented with collective quantum jumps, since a given photocount cannot be assigned, in principle, to an emission from any particular atom. Correspondingly, under these conditions the associated master equation involves collective radiative damping terms [2], in a form that tends towards the Dicke model for atoms occupying a volume much smaller than a wavelength cubed.

© 1998 IEEE