【作者】 毕冬艳；

【导师】 李永放；

【作者基本信息】 陕西师范大学 ， 光学， 2004， 硕士

【摘要】 早在量子力学全盛时期人们就对量子隧道效应有所认识，这是量子力学的基本问题。1927年Hund就提出了量子隧道效应会对（如NH₃）三角锥形分子的内部结构有很大的调整作用，所以通过适当选择外部条件，便可在不同程度上控制分子结构的稳定性。随着量子通讯和量子计算的发展，特别是半导体量子阱技术的日渐成熟，极大的提高了量子阱的实用化发展。因此近些年来，人们十分关注分子和半导体量子阱中双势阱的量子隧穿效应的研究。于是粒子在双势阱中受外场驱动的量子力学行为便成为近年来人们研究的热点问题之一。 外加电磁场作用下二能级系统和三能级系统的演化是许多实际应用的理论基础。新兴学科分子电子学其进展包括分子导线和分子开关。分子导线是利用了能使电子非局域化的分子结构，将电子从集成的分子装置的一个区域移动到另一个区域。分子开关则是一些在外电场、光场、化学或生物作用下可以发生结构或其它状态改变的分子，它们有希望被用了来作为开关器件和存贮单元等。很多的这些器件表现出一种两能级隧穿的特性，比如有些分子材料的导电性就是通过电子从分子的一部分到分子的另外一部分的隧穿或跳跃来实现的；有的分子开关则是利用了分子的机构互变现象，而这往往也就是电子、质子、氢原子、甚至原子基团的隧穿现象。如果能够通过改变外界条件来控制这些隧穿过程，我们就可以操纵这些器件。 本文的第一个主要工作是利用二能级近似研究了受驱动光场作用时的粒子在双势阱分子中的量子隧道效应抑制现象。讨论了在远共振激发，和在强场激发情况下的粒子定域问题。在处理方法上从二能级系统的哈密顿量出发，得出系统的本征矢，它不但适合远共振激发极限，同时也适合于强场激发极限。从而克服了以往将两极限分开讨论的缺陷，以简单的形式获得了内涵深刻的物理结论。即，在0阶贝塞尔函数为0时，系统将永远保持起始的定域状态，而不发生隧穿。在强场极限下，利用贝塞尔函数的渐近行为，得出关系系统本质的相位解释。实现了处理方法和形式上的简单化，物理意义的清晰化。 本文的第二个主要工作是，讨论了当单独的一个孤立的分子被镶嵌在一个主体的媒质中时，形成上势阱不对称下势阱是对称的特殊模型，对称势阱对应的是电子的非激发态，非对称势阱对应的是激发态。本文就对这一特殊系统进行讨论。在一近共振外场的作用下，上下两势阱便联系起来，形成一Λ型三能级系统。在这种情况下，系统将会发生相干隧穿抑制现象，也即相干布居数捕获现象，粒子完全定域在初始的势阱中。本部分内容分别用缀饰态和明黑态对这一问题作了分析，通过一些近似，得出结论，明黑态的分析对这一特殊系统发生相千隧穿抑制现象作了物理解释。最后一部分数值的分析，更是详细的讨论了外加的激光场对系统隧道效应的影响，并特别的讨论了外场对于左右阱间和上下阱间粒子数布居分布的影响状况。在一定的情况下粒子不但可以被定域在各自所处的阱里，而且可以完全定域在较低的势阱里。更多还原

【Abstract】 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.更多还原