Dynamic Properties Of Atoms In Standing Wave Laser And Teleportation Of Quantum States

This thesis investigates the basic theory of cooling and trapping atoms under the interaction of radiation light pressure. Through the non-locality of the quantum entanglement, teleportation schemes of arbitrary two-particle and three-particle states are proposed.Laser cooling and trapping rely on the interaction between laser light and atom and the transfer of energy and momentum from the optical field to the atom. Using laser radiation, it is possible to decrease the atomic velocity, cool atomic gases and trap the cooled atoms. In this thesis, a semi-classical model of the force on an atom is used to describe the motion of a two-level atom interacting with a standing wave laser field. The velocity dependent force and momentum diffusion are derived through optical Bloch equations by using the matrix form of the continued fraction technique. By investigating the dynamic properties of atoms in laser field, we can control and manipulate the mechanical motion of an atom. Therefore, by exerting controllable atomic array and quantum states, it is possible for physical realization of a quantum computer and the communication of quantum states.It is shown that a negative detuning of the laser field from the atomic resonance will lead to nonzero light pressure forces and reduce velocities along the laser beam axis. When the intensity of the laser field is weak, the velocity dependence of the average longitudinal force has the Doppler shifted Lorenztian resonance. At high intensities, there is a kink and change direction of the light pressure force near the point of zero velocity, the effects of the higher order harmonic light pressure forces become significant. It is seen that the behaviors of light pressure forces with even order are similar to the zero order force while that of odd order forces are opposite to the zero order one. Though the whole effects of the odd order and even order harmonic forces are almost destructive with each other for strong intensity, it is quiet different compared to the case of weak intensity. For weak intensity, the higher order harmonic forces can be neglected. If the velocity of atoms is near to zero, the light forces will tend to confine the atoms near to nodes and antinodes. The stability depends on the magnitude of the negative slope of the light force, the depth of the potential well andthe momentum diffusion coefficient. It is important to select the parameters, e.g. the detuning and the intensity of the light field, in order to enhance the efficiency of trapping atoms.Quantum entanglement, a basic phrase for superposition in a multi-particle system, has become a new focus of activity in the field of quantum information science. Teleporting an unknown quantum state is an important example. In this thesis, the preparation and measurement of Bell states of two particles are introduced. A scheme for teleportation an arbitrary three-particle state is proposed, which is possible to extend for teleporting an arbitrary N-particle state. In terms of the basic logic gates, the quantum logic circuit for teleporting a qubit and an arbitrary two-particle state are also presented.Teleportation of an unknown quantum state includes three processes, preparing entangled EPR states, performing joint Bell state measurements on the particle that will be teleported and one particle of the EPR state, and then performing a unitary transformation on the second particle of the EPR state. A scheme for teleporting an arbitrary three-particle state is proposed. It is necessary to set up three distant entangled pairs. Alice performs a joint Bell state measurement on her particles three times. She informs Bob the results of her measurements through classical channels. Bob then performs a unitary transformation on his particle. The original quantum state can be recovered. The probability of successful teleportation is related to the quantum channel. If the quantum channel is composed of three maximally entangled particle pairs, the total probability of successful teleportation equals one, which...