Quantum Dynamical Model's Decoherence In Macroscopic Limits

Quantum decoherent study has an important meaning in the field of quantum measurement. Because it is necessary to induct classical meter, it come into being entangle between the classical meter and the measured system through the system-meter interaction. When the density matrix of the whole ensemble consisted of system-meter is reduced to the microscopic physical system, the system trend quantum decoherence in nature. However , on the other hand, quantum information processing and quantum computing need stable coherent superposed state, then decoherence is a difficulty of realizing them, it is, therefore, an important issue to find methods for slowing down decoherence in order to stabilize the coherent superpositions in the field of quantum study. In this paper, we deduce the decoherent factor in theory, and then we control decoherence by varying coupling coefficient.In this paper, there are two parts. In one part, we put forward a kind of decoherent process and decoherent control of quantum dynamical model. The interaction of the meter and the system are divided into two sections. First, the interaction is damping interaction and potential energy. We deduce easily the coherent term of quantum dynamical model (the off-diagonal of reduced density matrix) by improving the nature of displace operator and the nature of coherent states. Then, the interaction is energies of a two-photon mechanism and the usual one-photon or liner driving mechanism. We deduce the coherent term by improving the nature of squeezing operators, displace operators and canonical transformation. On the one hand, we deduce the off-diagonal term of reduced density matrix is inner-product of two coherent states and we carry out decoherence in macroscopic limits in two special case, On the other hand, we delaydecoherent time by controlling the interaction coefficient. In other part, we define two kind independent phase operators by improving two-mode squeezing coherent states in two-mode phase space and resolve their eigenstates. And we obtain their annihilation operator and creation operator by improving canonical transformation to harmonic oscillator's annihilation operator and creation operator. More, we generalize supersymmetric harmonic oscillator space. In this space, we construct two kinds independent phase operators by improving supersymmetric annihilation operator and supersymmetric creation operator, and then obtain their eigenstates. The common of the two parts is the use of entangled state and its nature. In one part, the evolution wave-function of the composite system consisted of system and meter is an entangled state. Because of the special nature of entangled state, the system carry out decoherence. In other part, the eigenstates of two kinds of phase operators are entangled states. In a word, they are a kind use of entangled state.If we can control freely system decoherence, we can realize quantum communications and quantum computer. So it is a primary signification to whether control decoherence or not. In this paper, we can control the system decoherence by control magnitude and type of interaction, which can enlighten in theory people well on studying quantum communications and developing quantum computer.