The Dynamics Of The Dipole-dipole Interaction In The Atomic Ensembles

In this thesis,we mainly study the dynamics involving the interatomic dipole-dipole interaction and its application in quantum information processing.In Chapter 1,firstly,we introduce the basic mechanism and the classifcation of the dipole-dipole interaction in detail.Then,we outline the related aspects to our research results for the cavity quantum electrodynamics and the Rydberg atom system.Since the coupling of quantum system to the environment will lead to decoherence process,we thus have to introduce the theoretical tools,such as master equation or the quantum jump method,to describe the dissipative dynamics.Finally,we introduce the fundamental theory of an adiabatic process that will be used for the implementation of quantum logic gate based on the Rydberg atom system.In Chapter 2,the effect of the dipole-dipole interaction on the quantum electrodynamics and the photon statistics of the system with two atoms trapped in an optical cavity is discussed by the method of quantum jump.In the cavity quantum electrodynamics system,the standard Jaynes-Cummings(JC)model describes the interaction of a two-level atom with a single-mode quantized cavity field.The atom-cavity strong coupling results in the anharmonic JC ladder of the dressed energy levels and the photon blockade,which then leads to the generation of the nonclassical cavity transimision.Here,we sutdy the correlation of the dipole-dipole interaction and the transmitted two-photon second-order correlation function with two atoms trapped in an optical cavity driven by a laser field and subjected to cooperative emission.We have found that by modulating the interatomic dipolar coupling,the photon statistics described by the equal-time second order correlation function can vary from bunching to antibunching for both resonant and non-resonant atom-field interaction,which may be significantly useful in quantum information processing and quantum communication.In Chapter 3,we put forward two new schemes for implementing the quantum phase gate(QPG)via the adiabatic passage and phase control of the laser fields.The first scheme is based on the geometric operation via adiabatic process,however,the geometric phase acquired in the cyclic evolution of the system is not due to variance of the phase difference of the laser pulse,but is come from evolution of the phase of Rabi frequency itself.The second schemes is completely different from the normal dynamical and geometric phase gates,neither does the qubit system undergo any dynamical phase shift since it works in the dark space nor does the Hamiltonian need to change along the suitable loop involving a required solid angle.Thus,the conditional phase is of neither dynamical nor geometric origin.It arises from the adiabatic evolution of the dark eigenstate itself under laser-phase control.In comparison with the geometric phase gate,it does not require the parameters to sweep a required solid angle,and thus the procedure is simplified and the errors in the adiabatic phase control are avoided,which provides a promising approach for quantum computation on account of the Rydberg blockade mechanism.