双量子阱中光子辅助电子自旋隧穿

采用单电子有效质量近似理论, Floquet理论和传递矩阵方法, 对包含时间周期场的双量子阱中单电子的自旋隧穿特性进行了研究, 对InP/InAs半导体材料进行了数值计算. 重点研究了Rashba型和Dresselhaus型自旋轨道耦合、量子阱结构以及偏压对电子隧穿的影响. 这些结果可以为设计和调控半导体自旋电子器件提供一定的理论依据. 关键词： 光子辅助隧穿 隧穿概率 量子阱     

光子晶体双量子阱的共振隧穿

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     

有效质量法调控原子玻色-爱因斯坦凝聚体的双阱动力学

操控原子玻色-爱因斯坦凝聚体在双势阱中的动力学通常是通过改变势阱深度来实现,本文提出了一种基于调节原子有效质量的控制方案,可以在不改变双阱势的前提下操控凝聚体的双阱动力学.利用双模近似,本文解析地导出了超冷原子在双阱势中的隧穿强度和相互作用强度对有效质量的依赖关系,并基于平均场近似数值模拟了在有效质量调节下的凝聚体动力学演化,展示了隧穿振荡和自束缚等典型的双阱动力学行为.此外,本文的研究还发现,借助负有效质量效应,这一方案甚至可以等效地实现对负散射长度原子凝聚体双阱动力学行为的操控.     

Resonant tunneling and confining phenomena in symmetrical rectangular triple-barrier structures with c-type deep wells

Theoretical study of resonant tunneling is carried out in rectangular triple-barrier structures with C-type deep wells. Analytical expressions for the transmission coefficient and the resonance conditions are derived. Transmission characteristics versus electron energy are investigated and it is shown analytically that the transmission spectrum is a Lorentzian in form near energies of resonance. It is confirmed that the resonance energy is almost equal to the eigenenergy of the double-well structure. Moreover, wave functions of an electron at the resonance level are examined and the confining phenomenon is studied.     

Magnetic-field-induced singularity in the tunneling current through an InAs quantum dot

The tunneling transport through a GaAs/(AlGa)As/GaAs single-barrier heterostructure with self-assembled InAs quantum dots is studied experimentally at low temperatures. An anomalous increase in the tunneling current through the quantum dots is observed in magnetic fields both parallel and perpendicular to the current. This result cannot be understood in the framework of the single-electron approximation. The proposed explanation of the phenomenon is based on the modified Matveev-Larkin theory, which predicts the appearance of a singularity in the tunneling current through the zero-dimensional state in a magnetic field because of the interaction between the tunneling electron and the spin-polarized three-dimensional electron gas in the emitter. The absence of spin splitting in the experimental resonance peaks is caused by the complete spin polarization of the emitter in relatively weak magnetic fields.     

量子遂穿在双阱异核分子形成过程中的作用(英文）

对于束缚在双阱中的两组分玻色－爱因斯坦凝聚体,本文研究了基于光缔合机制形成分子的过程中,量子隧穿所起的作用．该双阱外势可以在实验上利用磁场生成的谐振子势和由蓝失谐光或射频源生成的中心势垒来实现．在合适的光场中,我们分析了系统在不同初始状态下的短时极限量子动力学,同时对系统做了在平均场近似下的数值计算分析．我们发现无论是隧穿强度还是初始状态的制备都对系统的动力学有很大的影响．我们还计算了同核分子在这些情况下的结果,并和异核分子计算的结果作了比较．量子化的光缔合光场在分子形成过程的影响也在文章中给予了讨论．     

The effects of two-dimensional bifurcations and quantum beats in a system of combined atomic force and scanning tunneling microscopes with quantum dots

The field and temperature dependence of the probability of two-dimensional dissipative tunneling is studied in the framework of one-instanton approximation for a model double-well oscillator potential in an external electric field at finite temperature with account for the influence of two local phonon modes for quantum dots in a system of a combined atomic force and a scanning tunneling microscope. It is demonstrated that in the mode of synchronous parallel transfer of tunneling particles from the cantilever tip to the quantum dot the two local phonon modes result in the occurrence of two stable peaks in the curve of the 2D dissipative tunneling probability as a function of the field. Qualitative comparison of the theoretical curve in the limit of weak dissociation and the experimental current–voltage characteristic for quantum dots that grow from colloidal gold under a cantilever tip at the initial stage of quantum-dot formation when the quantum dot size does not exceed 10 nm is performed. It is established that one of the two stable peaks that correspond to interaction of tunneling particles with two local phonon modes in the temperature dependence of the 2D dissipative tunneling probability can be split in two, which corresponds to the tunneling channel interference mechanism. It is found that the theoretically predicted and experimentally observed mode of quantum beats occurs near the bifurcation point.     

玻色-费米混合气体的非线性Landau-Zener隧穿

在有相互作用的非线性两模系统中, 通过对相互作用参数的调节, 研究了该系统中玻色-费米混合气体的Landau-Zener隧穿现象. 研究发现, 其中某一组分的自相互作用会影响另一组分粒子的隧穿, 使得隧穿出现临界现象. 关键词： 玻色-费米混合气体 Landau-Zener隧穿 量子绝热隧穿     

Macroscopic resonant tunneling in the presence of low frequency noise

We develop a theory of macroscopic resonant tunneling of flux in a double-well potential in the presence of realistic flux noise with a significant low-frequency component. The rate of incoherent flux tunneling between the wells exhibits resonant peaks, the shape and position of which reflect qualitative features of the noise, and can thus serve as a diagnostic tool for studying the low-frequency flux noise in SQUID qubits. We show, in particular, that the noise-induced renormalization of the first resonant peak provides direct information on the temperature of the noise source and the strength of its quantum component.     

Resonance breakdown of a Coulomb blockade due to the mechanical vibrations of a quantum dot

The effect of forced mechanical vibrations of a suspended single-electron transistor on Coulomb-blockade limited electron tunneling through a quantum dot has been studied. The mechanical vibrations of the quantum dot have been shown to result in the Coulomb blockade breakdown, which is manifested by narrow resonance peaks of the transistor conductance as a function of the excitation frequency at the frequencies corresponding to the eigenmodes of the mechanical vibrations. The mechanism of the observed effect presumably associated with the oscillations of the mutual electrical capacitances between the quantum dot and the surrounding electrodes is discussed.     

Single-photon tunneling via localized surface plasmons

Strong evidence of a single-photon tunneling effect, a direct analog of single-electron tunneling, has been obtained in the measurements of light tunneling through individual subwavelength pinholes in a gold film covered with a layer of polydiacetylene. The transmission of some pinholes reached saturation because of the optical nonlinearity of polydiacetylene at a very low light intensity of a few thousand photons per second. This result is explained theoretically in terms of a "photon blockade," similar to the Coulomb blockade phenomenon observed in single-electron tunneling experiments. Single-photon tunneling may find applications in the fields of quantum communication and information processing.     

RESONANT TUNNELING THROUGH COUPLED DOUBLE-QUANTUM-WELL

A double-well resonant tunneling structure has been investigated carefully using the nonequilibrium Green's function method. We find that in the transmission probability two maxima appear even when the two levels have the same energy. This characteristic is at-tributed to the resonant tunneliug through mixed quasibound states. The tunneling current formula through this system under a dc voltage has been derived exactly. Three different cases are considered and several novel properties are found, which manifest coherent charac-teristics of the tunneling process.     

Landau-Zener tunneling of Bose-Fermi mixture in double-well

The nonlinear Landau-Zener tunneling of a Bose-Fermi mixture in a double-well potential is studied in the present paper. The effect of interaction parameters on bosonic and fermionic tunneling probability is studied for the mixture of ⁴⁰K-⁸⁷Rb. The tunneling phenomena of the system can be controled by adjusting sweeping rate, intraspecies interaction, interspecies interaction and the numbers of bosons and fermions. It is noted that there are three different regions in phase diagram: self-trapping (ST), complete tunneling (CT) and incomplete tunneling (ICT).     

Quantum transport signatures of non-trivial topological edge states in a ring-shaped Su–Schrieffer–Heeger double-chain system

In the ring-shaped Su–Schrieffer–Heeger(SSH)double-chain,the quantum interference between the two different electron tunneling paths of the upper and lower chains has an important influence on the electron transport properties of non-trivial topological edge states.Here,we have studied the electron transport signatures of non-trivial topological edge states in a ring-shaped SSH double-chain system based on the wave-guide theory and transfer-matrix method.In the ringshaped SSH double-chain with the upper chain being different from the lower one,it is demonstrated that the electron transmission probability displays the four and two resonance peaks associated with the non-trivial topological edge states in the weak and strong coupling regimes,respectively.Whereas in the case of the upper chain being the same as the lower one,the two transmission resonance peaks associated with the non-trivial topological edge states in the weak coupling regime are only found,and that in the strong coupling regime disappear that originated from the destructive interference between the two different electron tunneling paths of the upper and lower chains.Consequently,the variation of the number of transmission resonance peaks associated with the non-trivial topological edge states in the weak and strong coupling regimes suggests that an alternative scheme for detecting non-trivial topological edge states in the ring-shaped SSH doublechain system.     

Effect of Cavity Decay on the Coherent Control of Atomic Tunneling

In this paper we study the influence of cavity decay on the atomic tunneling and entanglement dynamics in a cavity QED system. The system consists of an atom in a double-well potential and a cavity. The results show that the cavity decay affects significantly the tunneling and the entanglement dynamics. The tunneling behaves as a damping-oscillating function of time in this case, while the entanglement shared between the internal and external degree of freedom of the atom exhibits the so-called entanglement sudden death (ESD).     

Voltage-controlled spin selection in a magnetic resonant tunneling diode

We have fabricated all II-VI semiconductor resonant tunneling diodes based on the (Zn,Mn,Be)Se material system, containing dilute magnetic material in the quantum well, and studied their current-voltage characteristics. When subjected to an external magnetic field the resulting spin splitting of the levels in the quantum well leads to a splitting of the transmission resonance into two separate peaks. This is interpreted as evidence of tunneling transport through spin polarized levels, and could be the first step towards a voltage controlled spin filter.     

Dynamics of a cold quantum gas in a δ-split one-dimensional potential well

Dynamics of a wave function in a non-symmetrically split (spatially asymmetric) doublewell potential is considered. We study the dependence of the probability of well-to-well transitions on the degree of spatial asymmetry of well sizes and show that the quantum tunneling between the wells is significantly suppressed by this asymmetry. Practically complete suppression occurs at five-ten percent asymmetry. This is close to the threshold of sensitivity of contemporary experimental schemes for creating two-well potentials. We predict the phenomenon of resonance in quantum tunneling of considered states. We have also shown that an incoherently prepared superposition state tunnels in a double-well potential almost in the same way as a perfectly coherent state.     

Coupling Effect of Atomic Tunneling States with Local Vibration Modes in Amorphous Materials1

Considering the coupling of the atomic tunneling states with the vibration modes of its nearby atoms, two different kinds of double-well potentials are obtained. At the meantime, the vibration of nearby atoms are softened, and under certain conditions a new double-wel1,potential of higher rank can be induced which makes a hierarchical double-well potential structure possible.     

Nonlinear Landau-Zener tunneling of Bose-Einstein condensate in a spatially magnetic modulated trap

We study tunneling of a Bose-Einstein condensates confined in a effective double-well potential (a single well with a spatially magnetic modulated scattering length, actually), called pseudo double-well trap, in which the interaction of atoms characterized by the s-wave scattering length a _s can be widely tuned with a magnetic-field Feshbach resonance. As a result, corresponding to different nonlinear parameters, the energy levels of the nonlinear Schrödinger equation can have complex structures in their dependence on the bias between the wells. We discuss the emergence of looped levels, which lead to a breakdown of adiabaticity that the Landau-Zener transition probability does not vanish even in the adiabatic limit. Moreover, we also find that the Landau-Zener tunneling in the pseudo trap show many striking properties distinguished from that of the real trap model (where the barrier is created by the external potential). Possible experimental observation in an opticallyinduced photonic lattices in a photorefractive material is suggested.