Abstract

The state of an atom undergoing spontaneous decay can be represented as an ensemble of pure-state trajectories. In the Monte-Carlo wave function description each trajectory displays continuous evolution in finite intervals, which are embraced by instants where a discontinuous quantum jump occurs. The continuous part of each history has been shown to coincide with the evolution according to the neo-classical radiation theory [1], which corresponds to an atomic decay proportional to $-\text{tanh}\frac{1}{2}\Gamma t$. Similar damping curves also occur in simple models of superfluorescence, where it represents the full average decay, including quantum jumps. This raises the question what single runs would look like for a superfluorescent system. This is the motivation for our study of quantum trajectories for the Dicke system for various values of the number of atoms. For simulations in terms of quantum jumps we find that the continuous evolution between jumps can lead either to a decrease or an increase of the energy. For a spin coherent state the energy increase occurs when the Bloch spin vector lies on the upper half of the Bloch sphere. Likewise, a quantum jump corresponding to spontaneous emission can also lead to an increase of the energy. Both cases of this unexpected increase of the energy can be experimentally observed in principle by selecting a proper sub-ensemble of single runs [2].

© 1996 IEEE