Study Of The Tunneling Effect In W-type Double Well

The tunnel effect was recognized long ago during the heyday of quantum mechanics. Inl927, Hund demonstrated that quantum tunneling is of importance for intermolecular rearrangements in pyramidal molecules such as ammonia. So, through selecte external force, we can control tunneling and control the frame of moleculars. Fast development of quantum communication and quantum calculation and especially the maturity of quantum semiconductor potentials technology enhance the application of quantum well largly.The time evolution of the two-level system and three-level system which interact with a laser field is the theory base of many practical application. Molectronics is one of the rising subjects. It include molecular wire and molecular swich. The molecular wire is based on molecular weight which can make electron delocalized. It can make electron move from one area to another area in one compositive molecular equipment. Molecular swich is moleculares whose configuration and other states can be changed under exterior electric field or photic and chemic and biologic effect. They can be used as swich device and storage location. Many of these device exhibite two level tunneling characteristic, for example, the electric character of some molecular material is realized through the tunneling effect of electron from one area to another; Some molecular swich is using the tautomerism of molecular framwork, this sometimes is the tunneling effect of electron or proton or hydrogen atoms. If we can control these tunneling process through some outside effect, we can control these device.In this peper, first, some aspects of quantum tunneling of a particle in a double-well of molecules driven by an external field are studied within the two level approximations. The localization problems of particles are studied when the system are driven by far off-resonance and/or strong laser fields. From the Hamiltonian of two level system we got the eigenvectors, they are right for the two limitations. Instead of discuss the two limitations one by one; we get simple expression with profound meaning. Our system will remain loclization in one of the well whenever the parameters of the driving field are so tuned that the zeroth Bessel funtion attains a zero. From the asymptotics behavior of the Bessel fuctions in the strong -field regime we got the stokesphase. Thus we abtainde smpliy means and simply form and cleanout the physical meaning.Second, suppression of Quantum Dynamical tunneling is predicted to occur when a laser field drives a transition in an isolated, single molecule embedded in a host medium. The system is characterized by two electronic states with double-well potentials for the ground [Vg(x)] and excited [Ve(x)] states. The unexcited ground state is sysmetric and the exited states is asymmetric. A external force having quasiresonant frequency drives trasitions between the ground and excited states, form a A type system. We dicussed this problome in two represetation, one is dressed represetation the other is dark and bright represetation. By some approximation we gained the solution and a physical interpretation, through numerical result we particular discussed the infection of tunneling by the laser field, and on some condition, particles can be complete localized in one well or be localized in lower doublet.