Theoretical Study On The Quantum Decoherence

Quantum correlation is very important in quantum mechanics. It can be said that, quantum correlation is the basic features in which quantum mechanics is different from classical mechanics. Almost all the quantum phenomena which are in conflict with classical physics is the direct or indirect consequence of quantum correlation. Quantum decoherence is so important in the field of quantum measurement. And it is unavoidable to introduce classical meters which come into being entangled with the measured system through the interaction. On the other hand, quantum information processing and quantum computing need stable coherent superposed state, then decoherence is a difficulty for the realization of such states. Therefore, an important issue is to find the schemes to reduce the effect of decoherence in order to stabilize the coherent superpositions in the field of quantum information.In this paper, we use a model in which the quantum dephase would occur to show the dynamical evolution of decoherence. The concepts and physical meanings are introduced briefly in the first part. By the commonly theory of quantum decoherence, we study its dynamic processing of quantum decoherence. The dynamical mechanism for the above system is described also. The decoherence factor and its time-dependence are studied by using Wei-Norman algebraic methods and the related properties of density operator. It can be found that the full decoherence will occur in the condition of macroscopic limit. The derivation shows that the quantum entropy will increase during the period of decoherence, and it can be regarded as one parameter to weigh the process of dephase. Finally, the dependence of fidelity on the decoherence factors is studied. The influences of the slow variables of the environment or the detector on the coherence properties of the quantum system described by fast variable are studied in detail with Born-Oppenheimer approximation. The general conclusion resulted from our research are that the fast motion of the system can be separated from the slow motion of the environment or the detector. When the motion of the environment or the detector satisfying the classical limit condition, the adiabatic state of the system will lost its quantum coherence. The decoherence factor was found depending on the character of displace operator and coherent states.