Decoherence of a two-state atom driven by coherent light (6 pages)

Hyunchul Nha, H. J. Carmichael

Recent studies of the decoherence induced by the quantum nature of the laser field driving a two-state atom [J. Gea-Banacloche, Phys. Rev. A 65, 022308 (2002); S. J. van Enk and H. J. Kimble, Quantum Inf. Comput. 2, 1 (2002)] have been questioned by Itano [W. M. Itano, Phys. Rev. A 68, 046301 (2003)] and the proposal made that all decoherence is due to spontaneous emission. We analyze the problem within the formalism of cascaded open quantum systems. Our conclusions agree with the Itano proposal. We show that the decoherence, nevertheless, may be divided into two parts---that due to forwards scattering and to scattering out of the laser mode. Previous authors attribute the former to the quantum nature of the laser field.

Syed Jamal Anwar, Sayyam, M. Usman

Wu Shu

The field entropy evolution in a system of the Schrodinger cat state light field interacting with a two-level atom was studied by solving Milburn equation.The influence of intrinsic decoherence,the strength of light field and the phase angle between the two coherence states on the field entropy evolution was discussed.The results show that the field entropy vibration will be weak gradually because of the intrinsic decoherence,and the degree of entanglement in the field-atom system approaches to a certain value with time evolution.Furthermore,the degree of entanglement in the field-atom system only depends on the strength of light field and the phase angle between the two coherence states,and have nothing to do with intrinsic decoherence.When the strength of light field is relatively small,the degree of entanglement is maximum in a system of a two-level atom interacting with an odd coherence state light field,and it is minimum in a system of a two-level atom interacting with an even coherence state light field;it is intermediate for a system of a two-level atom interacting with Yurke-Stoler coherence state light field.When the intrinsic decoherence is fixed and the strength of light field is relatively large,the degree of entanglement in the field-atom system existing in the Yurke-stoler,the even coherence state and odd coherence state tends to the same.

Yvan R. P. Sortais

Poonam Yadav, Arnab Ghosh, Vikash Kumar Yadav +1 more

Abstract Hyperfine ground states in alkali atoms are among the most promising candidates for realizing high fidelity scalable quantum information processing architecture. Fast manipulation of ground states can be realized via two-photon transitions driven by lasers. The light-atom interaction can cause decoherence in the system. Here, we study the decoherence rate using accurate lineshape spectroscopy involving hyperfine ground states of D2 transition in 133 Cs atoms in room-temperature-atomic-vapor. The measured decoherence rate varies very slowly as a function of the Rabi frequency of the probe field. Furthermore, we have investigated the slow light group velocity resulting from the narrow spectral width of the electromagnetically induced transparency lineshape. Our study paves the way to implement quantum information processing protocols using coherent photonic polarization qubits in an atomic medium across a large parameter range.

F. T. Arecchi, E. Courtens, Robert Gilmore +1 more