Influence of dipole-dipole interactions on decoherence-free states

Decoherence, known as the consequence of the coupling of any quan-
tum system to its environment, causes information loss in the system
and represents a major problem in the physical realization of quan-
tum computers [1]. Decoherence-Free States (DFS) are considered as a
possible solution to this problem. A set of trapped cold atoms placed
in a DFS state will be immune against decoherence due to sponta-
neous emission. However, because of dipole-dipole interactions between
atoms, induced dephasing effects are likely to destroy the coherence
and drive the system out of its DFS [1-2]. In this work, we study nu-
merically the dynamics of a set of two-level atoms initially in a DFS
with respect to dissipative processes by solving the master equation in-
cluding both dissipative dynamics and dipole dipole interactions. We
focus our attention on the influence of dipolar coupling on the radiated
energy rate and coherence of the system as in [3]. In particular, by av-
eraging over many realizations of close randomly distributed atomic
positions, we show the formation of a superradiant-like pulse and we
study its properties as a function of the dipolar coupling strength.
[1] D. A. Lidar & K. B. Whaley, Lectures Notes in Phys., Vol. 622,
p83-120, Springer (2003).
[2] M. Gross & S. Haroche, Physics reports 93, 301-396 (1982).
[3] W. Feng, Y. Li & S. -Y. Zhu, arXiv :1302.0957. (2013).