Coherent Control and Manipulation of atoms using femtosecond pulses

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Coherent control and manipulation of atoms is one of the central themes of research in atomic and optical physics owing to many potential applications including laser cooling, optical lattices, Bose-Einstein condensate, quantum information processing, high precession spectroscopy, and quantum computing. For many of these applications, it is highly desirable to produce samples of cold atoms whose population resides almost entirely in a particular quantum state. Primarily, two methods of coherent control are used to transfer the complete population to a particular state of atoms. These are stimulated Raman adiabatic passage (STIRAP) and adiabatic rapid passage (ARP). On the other hand, since the seventies of the last century, the laser induced forces, the so-called optical dipole force and the dissipative force, have been used routinely for the manipulation of atoms. The optical dipole force and the dissipative force have been used for the trapping of particles and cooling of atoms respectively. This particular area of research, i.e. coherent control and manipulation, is getting tremendous boost due to the recent technological developments in the generation of femtosecond pulses. In the context of coherent control, femtosecond lasers may be advantageous to realize ultrafast population transfer that is decoherence-free and robust. On the other hand, concerning manipulation of atoms or molecules using lasers, the magnitude of the dissipative force induced by commonly used CW lasers is limited due to spontaneous decay process. This limitation may be surmounted by using picosecond or femtosecond pulses, thereby realizing a very strong optical force. In this thesis, a detailed theoretical study is carried out on the manipulation and coherent control of atoms beyond the so-called rotating wave approximation (RWA). In the context of coherent control, we have studied the coherent population transfer (CPT) in two-, L -like three- and Y-like four-level atoms. This thesis also reports a study on the femtosecond pulse induced optical force on two- and three-level atoms in an atomic beam.
Supervisor: Amarendra Kumar Sarma