Photoluminescence asymmetry with quantum state preparation

We show that the number of photons in a strongly coupled exciton–photon system is asymmetric with the detuning of the modes when, in the spontaneous emission regime, the two modes are entangled. As changing the detuning is easy in semiconductor microcavities–where on the other hand the nature of the strong-coupling in terms of single-particle effects is not yet resolved–we propose this effect as a test of the quantum character of microcavity polaritons.     

Quantum dynamical study of the amplitude collapse and revival of coherent <Emphasis Type="Italic">A</Emphasis><Subscript>1g</Subscript> phonons in bismuth: a classical phenomenon?

We parameterize the potential energy surface of bismuth after intense laser excitation using accurate full-potential linearized augmented plane wave calculations. Anharmonic contributions up to the fifth power in the A _1g phonon coordinate are given as a function of the absorbed laser energy. Using a previously described model including effects of electron–phonon coupling and carrier diffusion due to Johnson et al., we obtain the time-dependent potential energy surface for any given laser pulse shape and duration. On the basis of this parameterization we perform quantum dynamical simulations to study the experimentally observed amplitude collapse and revival of coherent A _1g phonons in bismuth considering work of Misochko et al. Our results strongly indicate that the observed beatings are not related to quantum effects and are most probably of classical origin.     

Quantum radiation reaction effects in multiphoton Compton scattering

Radiation reaction effects in the interaction of an electron and a strong laser field are investigated in the realm of quantum electrodynamics. We identify the quantum radiation reaction with the multiple photon recoils experienced by the laser-driven electron due to consecutive incoherent photon emissions. After determining a quantum radiation dominated regime, we demonstrate how in this regime quantum signatures of the radiation reaction strongly affect multiphoton Compton scattering spectra and that they could be measurable in principle with presently available laser technology.     

纤锌矿InGaN staggered量子阱中的激子态和光学性质

本文将基于有效质量近似下的变分法,理论研究了纤锌矿InGaN/GaN staggered 量子阱中的激子态和光学性质。数值结果显示了InGaN量子阱中的量子尺寸和staggered受限垒对束缚于量子阱中的激子态和光学性质有着明显地影响。当阱宽增加时,量子受限效应减弱,激子结合能降低, 带间发光波长增加。另一方面,当量子阱中staggered受限势增加时,量子受限效应增强,激子结合能升高,带间发光波长降低。本文的理论结果证明了可以通过调节staggered垒高和量子尺寸来调控纤锌矿InGaN staggered 量子阱中的激子态和光学性质。     

纤锌矿InGaN staggered量子阱中的激子态和光学性质

本文将基于有效质量近似下的变分法,理论研究了纤锌矿InGaN/GaN staggered量子阱中的激子态和光学性质.数值结果显示了InGaN量子阱中的量子尺寸和staggered受限垒对束缚于量子阱中的激子态和光学性质有着明显的影响.当阱宽增加时,量子受限效应减弱,激子结合能降低,带间发光波长增加.另一方面,当量子阱中staggered受限势增加时,量子受限效应增强,激子结合能升高,带间发光波长降低.本文的理论结果证明了可以通过调节staggered垒高和量子尺寸来调控纤锌矿InGaN staggered量子阱中的激子态和光学性质.     

Field theory of mesoscopic fluctuations in superconductor-normal-metal systems

Thermodynamic and transport properties of mesoscopic conductors are strongly influenced by the proximity of a superconductor: an interplay between the large scale quantum coherent wave functions in the normal mesoscopic and the superconducting region, respectively, leads to unusual mechanisms of quantum interference. These manifest themselves in both the mean and the mesoscopic fluctuation behaviour of superconductor-normal-metal (SN) hybrid systems being strikingly different from those of conventional mesoscopic systems. After reviewing some established theories of SN quantum interference phenomena, we introduce a new approach to the analysis of SN mesoscopic physics. Essentially, our formalism represents a unification of the quasi-classical formalism for describing mean properties of SN systems on the one hand, with more recent field theories of mesoscopic fluctuations on the other hand. Thus, by its very construction, the new approach is capable of exploring both averaged and fluctuation properties of SN systems on the same microscopic footing. As an example, the method is applied to the study of various characteristics of the single particle spectrum of SNS structures.     

Dynamical symmetry breaking in SYM theories as a non-semiclassical effect

We study supersymmetry breaking effects in N=1 SYM from the point of view of quantum effective actions. Restrictions on the geometry of the effective potential from superspace are known to be problematic in quantum effective actions, where explicit supersymmetry breaking can and must be studied. On the other hand the true ground state can be determined from this effective action, only. We study the problem whether some parts of superspace geometry are still relevant for the effective potential and discuss whether the ground states found this way justify a low energy approximation based on this geometry. The answer to both questions is negative. Essentially non-semiclassical effects change the behavior of the auxiliary fields completely and lead to the demand of a new interpretation of superspace geometry. These non-semiclassical effects can break supersymmetry. Received: 10 January 2002 / Revised version: 13 April 2002 / Published online: 18 October 2002 RID="*" ID="*" Work supported in part by the Schweizerischer Nationalfonds RID="a" ID="a" e-mail: bergamin@tph.tuwien.ac.at     

Effects of hydrostatic pressure on intrawell and interwell excitons in a strained GaAs/GaAlAs double quantum well system

Binding energies of intrawell and interwell excitons are investigated in a GaAs/GaAlAs double quantum well system in the presence of hydrostatic pressure applied in the z-direction. Calculations have been carried out with the variational technique within the single band effective mass approximations using a two parametric trial wave function. The interband emission energy as a function of well width is calculated in the influence of pressure. The pressure dependent photoionization cross section for a charged exciton placed at the center of the quantum well is computed as a function of normalized photon energy. The dependence of the photoionization cross section on photon energy is carried out for the charged excitons. The resulting spectra are brought out for light polarized along and perpendicular to the growth direction. The results show that the charged exciton binding energy, interband emission energy and the photoionization cross section depend strongly on the well width and the hydrostatic pressure. Our results are compared with the other existing literature available.     

Polarization bremsstrahlung process in quantum plasmas including electron-exchange and shielding effects

The electron-exchange and quantum shielding effects on the polarization bremsstrahlung spectrum due to the electron-shielding sphere encounters are investigated in quantum plasmas. From this work, it is found that the electron-exchange effect strongly suppresses the polarization bremsstrahlung radiation cross section. Additionally, it is found that the polarization bremsstrahlung radiation cross section increases with increasing plasmon energy and, however, decreases with increasing Fermi energy. The variation of the influence of electron-exchange and quantum shielding on the polarization bremsstrahlung spectrum is also discussed.     

Dimensional crossover of quantum interference effects in thin quasicrystalline Al-Cu-Fe films

We present a study of the electrical transport properties of thin i-Al-Cu-Fe films. We observe clear signatures of a dimensional crossover in the temperature and magnetic field dependence of the conductivity for films thinner that ≃ 10³?. In particular for the thinnest sample the magnetoconductivity is strongly anisotropic, as is expected for the weak localisation contribution in two dimensions. These experiments show direct qualitative manifestations of the disorder induced quantum interference effects occurring in quasicrystals. Estimates of the electronic microscopic parameters are in accordance with those obtained in bulk samples. Their values and significance are discussed. Received 16 February 2001 and Received in final form 20 June 2001     

氢离子与里德伯原子碰撞中的电荷转移过程

应用双中心原子轨道强耦合方法研究了H⁺与里德伯态原子Li（5d）碰撞的电荷转移过程,计算了电子转移到氢原子各个n,l壳层（这里n为主量子数,l为角量子数）的态选择截面.结果发现,电荷转移的末态主要分布在与初态电子能量5d接近的n=4—7能级,该分布随碰撞能量的变化不大;但俘获末态的l分布对入射离子能量很敏感：在1 keV左右的低能时主要分布在高l的末态,随着碰撞能量增加峰值逐渐向低l方向移动,并在l= 关键词： 电子俘获过程 双中心原子轨道强耦合方法 态选择截面     

Coherent mesoscopic transport through a quantum dot-carbon nanotube system under two-photon irradiation

Mesoscopic transport through an ultrasmall quantum dot (QD) coupled to two single-wall carbon nanotube (SWCN) leads under microwave fields (MWFs) is investigated by employing the nonequilibrium Greens function (NGF) technique. The charging energy and junction capacitances influence the output characteristics sensitively. The MWFs applied on the leads and gate induce novel photon-assisted tunnelling, strongly associated with the density of states (DOS) of the SWCN leads. The SWCN leads act as quantum wires, and the compound effect induces nonlinear current behavior and resonant tunnelling in a larger region of energy scale. Negative differential conductance (NDC) is clearly observed, as the source-drain junction capacitances C _L , and C _R are large enough. The multi-resonant NDC oscillation appears due to the charging and photon-electron pumping effects associated with the contribution of multi-channel quantum wires.Received: 5 July 2004, Published online: 14 December 2004PACS: 73.40.-c Electronic transport in interface structures - 73.63.Fg Nanotubes - 73.61.Wp Fullerenes and related materials - 73.22.-f Electronic structure of nanoscale materials: clusters, nanoparticles, nanotubes, and nanocrystals     

The different effect of electron-electron interaction on the spectrum of atoms and quantum dots

Though atoms and quantum dots typically contain a comparable number of electrons, the number of discrete levels resolved in spectroscopy experiments is very different for the two systems. In atoms, hundreds of levels are observed while in quantum dots that number is usually smaller than 10. In the present work, this difference is traced to the different confining potentials in these systems. In atoms, the soft confining potential leads to large spatial extent of the excited electron's wave function and hence to weak Coulomb interaction with the rest of the atomic electrons. The resulting level broadening is smaller than the single particle level spacing and decreases as the excitation energy is increased. In quantum dots, on the other hand, the sharp confining potential results in electron-electron scattering rates that grow rapidly with energy and fairly quickly exceed the approximately constant single particle level spacing. The number of discrete levels in quantum dots is hence limited by electron-electron interaction, whose effect is negligible in atoms. Received 3 April 2000 and Received in final form 7 August 2000     

The relation of chemical potentials and reactivity studied by a state path sum

Exact quantum transition probabilities for collinear F + H₂ → FH + H on two different potential energy surfaces are analyzed in terms of regional effects of the potentials. The potentials considered are (a) a weakly curved rotated harmonic model potential and (b) a strongly curved rotated Morse potential fitted to the ab initio SCFCI surface of Bender et al. In both potentials a, b the energy along the reaction path has the same parameters, and three successive regions 1–3 are analysed. The main results are: (1) at very low total energies the reactants are reflected from the activation barrier (region 1 of potentials a, b). (2) in the downhill region 2 of potentials a and b the molecules are weakly and strongly excited, respectively. Region 2 of the realistic potential b also causes H₂ back reflection, depending on the total energy (although there is no barrier in region 2!); (3) In the final shallow sloped, weakly curved region 3 of potential a, part of the excited molecules are again de-excited before reaching the product's configuration. On the contrary, region 3 of potential b has a non-curved reaction path, and the reaction is adiabatic therein, i.e. the van der Waals minimum is irrelevant for vibrational excitation. Practical aspects of the state path sum method are discussed in detail.     

Quantum mechanical Monte Carlo approach to electron transport at heterointerface

With the progress of LSI technology, the electronic device size is scaled down to the sub 0.1μ m region. In such an ultrasmall device, it is indispensable to take quantum mechanical effects into account in device modeling. In this paper, we present a newly developed quantum Monte Carlo device simulation applicable to ultrasmall semiconductor devices. In this model, the quantum effects are represented in terms of quantum mechanically corrected potential in the classical Boltzmann equation. It is demonstrated that the quantum transport effects such as tunneling and energy quantization in ultrasmall semiconductor devices are obtained for the first time by using the standard Monte Carlo techniques.     

Oscillatory screening and quantum interference effects on electron collisions in quantum plasmas

The oscillatory screening and collision-induced quantum interference effects on electron-electron collisions are investigated in dense quantum plasmas. The modified Debye-Hückel potential with the total spin states of the system is considered to obtain the differential electron-electron scattering cross section in quantum plasmas. It is shown that the electron-electron scattering cross section decreases with an increase of the quantum wave number. In addition, the minimum position of the cross section has been appeared with increasing the collision energy at the scattering angle θL=π/4. It is also found that the oscillatory screening effects strongly suppress the cross section near θL=π/4. In addition, it is found that the quantum interference effects suppress the cross section, especially, for the forward and backward scattering cases.     

Bose-Einstein condensates with vortices in rotating traps

We investigate minimal energy solutions with vortices for an interacting Bose-Einstein condensate in a rotating trap. The atoms are strongly confined along the axis of rotation z, leading to an effective 2D situation in the x-y plane. We first use a simple numerical algorithm converging to local minima of energy. Inspired by the numerical results we present a variational ansatz in the regime where the interaction energy per particle is stronger than the quantum of vibration in the harmonic trap in the x-y plane, the so-called Thomas-Fermi regime. This ansatz allows an easy calculation of the energy of the vortices as function of the rotation frequency of the trap; it gives a physical understanding of the stabilisation of vortices by rotation of the trap and of the spatial arrangement of vortex cores. We also present analytical results concerning the possibility of detecting vortices by a time-of-flight measurement or by interference effects. In the final section we give numerical results for a 3D configuration. Received 16 December 1998 and Received in final form 18 March 1999     

Laser effects on the donor states in V-shaped and inverse V-shaped quantum wells

Laser effects on the electronic states in GaAs/ Ga_1−xAl_xAs V-shaped and inverse V-shaped quantum wells under a static electric field are studied using the transfer matrix method. The dependence of the donor binding energy on the laser field strength and the density of states associated with the impurity is also calculated. It is demonstrated that in inverse V-shaped quantum wells under electric fields, with an asymmetric distribution of the electron density, the position of the binding energy maximum versus the impurity location in the structure can be adjusted by the intensity of the laser field. This effect could be used to tune the electronic levels in quantum wells operating under electric and laser fields without modifying the physical size of the structures.     

Quantum confinements in highly asymmetric sub-micrometer device structures

With the ongoing miniaturization of MOSFET structures into the nanometer domain, experimental results suggest there are physical limits up to which one can reduce the gate lengths. Furthermore, it becomes progressively more difficult to overcome the short channel effects at small gate lengths. This has led the researchers in the industry to look for alternative device technologies. One solution to the problem are the asymmetric device structures. In this work, we have simulated a 50 nm asymmetric MOS device structure using a two-dimensional Monte Carlo Poisson particle-based solver, in which quantum effects have been taken into account via the effective potential scheme. The quantum effects in these small device structures lead to strong quantum confinement of the carriers at the semiconductor/oxide interface, thus affecting the device drive current and the threshold voltage. We also show that the Silvaco Atlas simulations performed on the same device structure using the energy balance model were strongly affected by the choice of the energy relaxation times.     

Quantum gravity effects on spectroscopy of Kerr-Newman black hole in gravity’s rainbow

The effects of quantum gravity on spectroscopy for the charged rotating gravity’s rainbow are investigated in this paper. By utilizing an action invariant obtained from particles tunneling through the event horizon, the entropy and area spectrum for the modified Kerr-Newman black hole are derived. The equally spaced entropy spectrum characteristic of Bekenstein’s original derivation is recovered. And, the entropy spectrum is independent of the energy of the test particles, although the gravity’s rainbow itself is the energy dependent. Such that, the quantum gravity effects of gravity’s rainbow has no influence on the entropy spectrum. On the other hand, due to the spacetime quantum effects, the obtained area spectrum is different from the original Bekenstein spectrum. It is not equidistant and is dependent on the horizon area. And that, by analyzing the area spectrum from a specific rainbow function, a minimum area with a Planck scale is derived for the event horizon. At this point, the area quantum is zero and the black hole radiation stops. Thus, the black hole remnant for the gravity’s rainbow is obtained from the area quantization. In addition, the entropy for the modified Kerr-Newman black hole is calculated and the quantum correction to the area law is obtained and discussed.