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61.
62.
The crossover from thermal hopping to quantum tunneling is studied. We show that the decay rate Γ with dissipation can accurately be determined near the crossover temperature. Besides considering the Wentzel-Kramers-Brillo uin exponent, we also calculate contribution of the fluctuation modes around the saddle point and give an extended account of a previous study of crossover region. We deal with two dangerous fluctuation modes whose contribution cannot be calculated by the steepest descent method and show that higher order couplings between the two dangerous modes need to be taken into consideration. 相似文献
63.
We have studied the dynamical behaviours of two electrons confined in a double quantum dot driven by rotating magnetic fields in terms of the theory of Lewis-Riesenfeld Hermitian invariants for the explicitly time-dependent Hamiltonian. The coherent spin oscillations in the dot provide a generation source for spin current. Exact solutions obtained allow us to investigate the dynamical properties of the spin localization for various initial localized states. 相似文献
64.
Using the tight-binding approximation and the transfer matrix
method, this paper studies the electronic transport properties
through a periodic array of quantum-dot (QD) rings threaded by a
magnetic flux. It demonstrates that the even--odd parity of the QD
number in a single ring and the number of the QD rings in the array
play a crucial role in the electron transmission. For a single QD
ring, the resonance and antiresonance transmission depend not only
on the applied magnetic flux but also on the difference between the
number of QDs on the two arms of the ring. For an array of QD rings,
the transmission properties are related not only to the even--odd
parity of the number $N_{0}$ of QDs in the single ring but also to
the even--odd parity of the ring number $N$ in the array. When the
incident electron energy is aligned with the site energy, for the
array of $N$ rings with $N_{0}={\rm odd}$ the antiresonance
transmission cannot occur but the resonance transmission may occur
and the transmission spectrum has $N$ resonance peaks ($N-1$
resonance peaks) in a period for $N={\rm odd}$ (for $N={\rm even}$).
For the array of $N$ rings with $N_{0}={\rm even}$ the transmission
properties depend on the flux threading the ring and the QD number
on one arm of the ring. These results may be helpful in designing
QD devices. 相似文献
65.
Neutronics studies of solid targets for spallation neutron source using Monte Carlo simulation 下载免费PDF全文
Neutronics studies for a solid target have been done with Monte Carlo high-energy particle transport code NMTC/JAM,when the proton beam with high kinetic energy bombards the target.The effect of the main parameters of the target on the neutron flux is discussed to optimize the target,which will be used for the concept design of the target of spallation neutron source.A target with its aspect ratio 1.5:1 or 2:1 gives the highest neutron flux.Tungsten is the most acceptable material from the technical and economical points of view.Beryllium as a moderating reflector can increase the neutron flux effectively. 相似文献
66.
67.
文章介绍了分子磁体中的量子隧穿和宏观量子效应理论和实验研究的新进展.分子磁体既有宏观磁体特性也呈现纯量子行为,例如磁化矢量的量子隧穿.文章作者解释了如何通过量子隧穿实现宏观量子相干(即薛定谔猫态的相干叠加)和量子态位相干涉.对隧穿率计算的瞬子方法,特别是有限温度隧穿理论及其在分子磁体量子隧穿中的应用也做了简要的阐述. 相似文献
68.
提出一种基于自旋相干态变换求解自旋-玻色模型基态的变分法, 并将其用于单原子模型, 得到旋波近似和非旋波近似情形下的解析基态能量和波函数, 特别是在光场与原子的弱、强耦合区域都与数值对角化结果符合得很好. 另外, 该方法也可以直接用于求解任意原子数的Dicke模型基态和相应的量子相变研究, 而通常基于Holstein-Primakoff变换的变分法, 原则上只适用于原子数趋于无穷的热力学极限情形.
关键词:
自旋相干态
变分法
J-C模型 相似文献
69.
采用R矩阵法研究了二维光子晶体双量子阱的共振隧穿特性.研究发现:光子晶体双量子阱的共振频率可以通过调节双阱的耦合强度来控制;对称双量子阱中,共振峰发生双劈裂;不对称双量子阱,共振劈裂消失.但是,由改变左手介质和右手介质在双阱中的排列顺序产生的阱介质不对称阱的共振劈裂消失与阱宽不对称的双阱产生的共振劈裂消失不一样.进一步对一维光子晶体量子阱分析后发现,前者是由光在左右手介质中传播的能流方向相反产生干涉相消而引起;后者是由阱宽不同,阱的本征模不一样而引起.
关键词:
光子晶体
双量子阱
R矩阵')" href="#">R矩阵
左手介质 相似文献
70.