Aharonov-Bohm Interferometer in a T-Shaped Quantum Dot Embedded in Majorana Bound States *

We theoretically study the spin-dependent transport properties of anAharonov-Bohm (AB) interferometer composed by a T-shaped quantum dot (QD)embedded in Majorana bound states (MBS). We use the equation of motion method tocalculate the conductance across the interferometer. We note that the conductance exhibitssensitive dependence on the MBS-QD coupling strength as well as the polarization strengthof the leads when the phase factor of AB ring changes periodically. The conductance shows a transitionfrom resonance to anti-resonance when the MBS-QD coupling strength changes from small to large. Also, there is different p-dependence conductance when the leads alignment changesfrom parallel to anti-parallel. These findings suggest that such a model could be used for a sensitivedetection of MBS interactions, exploiting the high sensitivity of conductance to the AB phase in theinterferometer.     

Control of Aharonov–Bohm oscillations in a AlGaAs/GaAs ring by asymmetric and symmetric gate biasing

The control of the Aharonov–Bohm effect on a AlGaAs/GaAs ring structure is studied by employing two in-plane-gates. By applying a gate voltage to one of the gates, a change of the oscillation pattern due to the additional potential induced in one branch of the ring is observed. The change of the oscillation frequency as well as the phase is attributed to the multi-channel transport. In case of a symmetric biasing, where both gates are biased simultaneously, a larger voltage is required to change the oscillation pattern than for the case when only one gate is used. This effect is explained by a partial compensation of the phase difference between both branches of the ring.     

Modification of Landau Levels in a 2D Ring Due to Rotation Effects and Edge States

The properties of a 2D quantum ring under rotating and external magnetic field effects are investigated. The Landau levels and their inertial effects on them are initially analyzed. Among the results obtained, it is emphasized that the rotation lifted the degeneracy of Landau levels. The second part deals with the electronic confinement in a 2D ring modeled by a hard wall potential. The eigenstates are described by Landau states as long as they are not too close to the ring edges. On the other hand, near the ring edges, the energies increase monotonically. These states are known as edge states. Edge states have a significant role in the physical properties of the ring. Thus, the Fermi energy and magnetization are analyzed. In the specific case of magnetization, two approaches are considered. In the first approach, an analytical result for magnetization is obtained but without considering rotation. Numerical results show the de Haas-Van Alphen (dHvA) oscillations. In the second approach, rotating effects are considered. In addition to the dHvA oscillations, the Aharonov–Bohm-type (AB) oscillations are verified, which are associated with the presence of edge states. The effects of rotation on the results are discussed and it is found that rotation is responsible for inducing AB oscillations.     

空间周期磁场中单电子量子点的能谱和磁化强度

研究了在空间周期磁场下,单电子量子点中电子的能谱和基态磁化强度,并对它们随周期磁场的各个参数(B、β、ψ)的变化作了分析.在计算中使用GaAs量子点模型,同时把二维各向同性谐振子的本征态作为基矢.计算发现,β对量子点的影响最大,β较小时,能谱和基态磁化强度与均匀磁场中的结果相似,反之则差别很大.在随β变化的能谱图中,大B较之小B表现出更丰富的谱线信息.当β足够大时,周期磁场对量子点的影响几乎为零.在计算中β越大,则所需的基的最少个数越多,否则计算结果不准确.     

Transferring and Bounding Single Photon in Waveguide Controlled by Quantum Node Based on Atomic Ensemble

We study the scattering process of photons confined in a one-dimensional optical waveguide by a laser controlled atomic ensemble. The investigation leads to an alternative setup of quantum node controlling the coherent transfer of single photon in such one dimensional continuum. To exactly solve the effective scattering equations by using the discrete coordinate approach, we simulate the linear waveguide as a coupled resonator array at the high energy limit. We generally calculate the transmission eoet~cients and its vanishing at resonance reflects the good controllability of our scheme. We also show that there exist two bound states to describe the localize photons around the cavity.     

Magnetic response of an electron gas in a quantum ring of non-zero width

An investigation of the magnetic moment of an electron gas in a quantum ring of non-zero width is made. Analytic expressions are obtained for the magnetic moment. For the magnetic moment of the system, the dependence on temperature and parameters of the ring are found and investigated in detail. De Haas–van Alphen and Aharonov–Bohm oscillations are investigated.     

Solution of the Dirac equation by separation of variables in spherical coordinates for a large class of non-central electromagnetic potentials

A systematic and intuitive approach for the separation of variables of the three-dimensional Dirac equation in spherical coordinates is presented. Using this approach, we consider coupling of the Dirac spinor to electromagnetic four-vector potential that satisfies the Lorentz gauge. The space components of the potential have angular (non-central) dependence such that the Dirac equation becomes separable in all coordinates. We obtain exact solutions for a class of three-parameter static electromagnetic potential whose time component is the Coulomb potential. The relativistic energy spectrum and corresponding spinor wave functions are obtained. The Aharonov–Bohm and magnetic monopole potentials are included in these solutions.     

Fano‐Majorana Effect and Bound States in the Continuum on a Crossbar‐Shaped Quantum Dot Hybrid Structure

Transport properties are investigated through a crossbar‐shaped structure formed by a quantum dot (QD) coupled to two normal leads and embedded between two 1D topological superconductors (TSCs). Each TSC hosts Majorana‐bound states (MBSs) at its ends, which can interact between them with an effective coupling strength. A signature of bound states in continuum (BIC) is found in the MBSs spectral function. By allowing finite inter MBSs coupling, BICs splitting is observed and shows projection in transmission for asymmetric coupling case as quasi‐BICs. As a consequence, it is also shown that the Fano effect, arising from interference phenomena between MBSs hybridization trough QD, is observed with a half‐integer amplitude modulation. It is believed that the findings can help to better understand the properties of MBSs and their interplay with QDs.     

Origin of Electron and Hole Charging Current Peaks in Nanocrystal-Si Quantum Dot Floating Gate MOS Structure

The nanocrystal-Si quantum dot （nc-Si QD） floating gate MOS structure is fabricated by using plasma-enhanced chemical vapour deposition （PECVD） and furnace oxidation technology. The capacitance hysteresis in capacitancevoltage （C - V） measurements confirm the charging effect of nc-Si QDs. Asymmetric charging current peaks both for electrons and holes have been observed in current-voltage （I - V） measurements at room temperature for the first time. The characteristic and the origin of these current peaks in this nc-Si QD MOS structure is in- vestigated systematically. Moreover, the charge density （10^-7 C/cm^2） calculated from the charging current peaks in the I - V measurements at different sweep rates shows that each quantum dot is charged by one carrier. The difference of charging threshold voltages between the electrons and holes charging peaks, △VG, can be explained by the quantum confinement effect of the nc-Si dots in size of about 3.5 nm.     

Determinant of Wave Operator as a Measure for Resonance and Bound States in One-Dimensional Potential Scattering System

The determinant of the wave operator or its transposed operator (source operator) works as a measure for resonance and bound states in one-dimensional potential scattering system. This fact is based on an identity proved here: the determinant of the wave or source operator equals to the transmission coefficient, which represents the field amplitude in the forward side of the scatterer. Utilizing this measure, resonance and bound states in one-dimensional system are properly assigned without solving wave equation. In future, local enhancement of optical near-field in three-dimensional system, i.e., local plasmon resonance will be treated, generalizing the present method.     

A Particle in a Magnetic Field of an Infinite Rectilinear Current

We consider the Schrödinger operator H=(i+A)² in the space L ₂(R ³) with a magnetic potential A created by an infinite rectilinear current. We show that the operator H is absolutely continuous, its spectrum has infinite multiplicity and coincides with the positive half-axis. Then we find the large-time behavior of solutions exp(–i H t)f of the time dependent Schrödinger equation. Our main observation is that a quantum particle has always a preferable (depending on its charge) direction of propagation along the current. Similar result is true in classical mechanics.     

Nature of the Electron Excited States and Energy Transfer in Bichromophore Coumarin Molecules

Results of experimental and theoretical research for three bichromophore molecules, trans-stilbene-CH₂-coumarin 120 (I), 4-methylumbelliferone-CH₂-UC 17, and 4-(3-fluoro)-methylumbelliferone-CH₂-UC 17 (II, III), are presented. Schemes of photophysical processes in the bichromophore molecules based on quantum chemical calculations by the INDO method and theory of radiationless transitions in polyatomic organic molecules are suggested. After optical excitation to the strong donor absorption band, the fast internal conversion processes develop there. As a result, the molecule is found in the S ₁ ^* -state localized on the acceptor moiety. It is shown that a mechanism of intramolecular transfer energy in bichromophores different from that proposed by Förster may be realized. Excitation energy, initially located on D, will be transferred from the donor moiety to the acceptor chromophore in convenience of the internal conversion process. The intramolecular electronic energy transfer from energy donor to energy acceptor may be interpreted as the internal conversion process. The rate constants of internal conversion are calculated.     

Plasma–wall transition in the quasi‐neutral region of collisional and stationary plasmas in a magnetic field enclosed by totally absorbing walls

The structure of stationary electron–positive ion plasmas in spatially limited vessels is analysed with special emphasis on the plasma–wall transition using different physical models. Basic investigations are carried out in a two‐fluid model, which is supplemented by ionization and oblique magnetic fields. Collisions between the two particle species were taken into account, as well as the dependence of the collision frequency on the particle density. For the case of non‐vanishing magnetic fields, electrons are not assumed to be in Boltzmann equilibrium. The investigated one‐dimensional domain is limited by totally absorbing walls on each side. Stationary states are considered, in which ionization sources balance the wall losses. To also take into account kinetic effects, simulations in a quasi‐neutral hybrid model are performed. The hybrid model assumes the electrons as a fluid and treats the ions using a particle‐in‐cell (PIC) method. A new way of ensuring the Bohm criterion is used by removing those superparticles impeding the wall. When comparing the results, both models reveal differences, especially when ionization from a resting neutral gas or weakly magnetized plasmas is considered, causing a broadening of the ion distribution or anisotropy effects, respectively.     

人工光学微纳结构中的连续体束缚态:原理、发展及应用

人工微结构可以捕获特定频率的电磁波,其为增强光与物质相互作用以及调控光场的重要平台之一.连续体束缚态在能谱上位于辐射连续区域,其是开放波动系统中与辐射连续态完全正交的本征态.连续体束缚态源于波动的相干相消,可以极大地抑制微纳光子器件的辐射损耗,为解决人工微纳结构中的光束缚提供全新思路.本文回顾连续体束缚态的发展历程,着...     

Scattering and bound states of spinless particles in a mixed vector–scalar smooth step potential

Scattering and bound states for a spinless particle in the background of a kink-like smooth step potential, added with a scalar uniform background, are considered with a general mixing of vector and scalar Lorentz structures. The problem is mapped into the Schrödinger-like equation with an effective Rosen–Morse potential. It is shown that the scalar uniform background present subtle and trick effects for the scattering states and reveals itself a high-handed element for formation of bound states. In that process, it is shown that the problem of solving a differential equation for the eigenenergies is transmuted into the simpler and more efficient problem of solving an irrational algebraic equation.     

Electron spin relaxation enhancement measurements of interspin distances in human, porcine, and Rhodobacter electron transfer flavoprotein-ubiquinone oxidoreductase (ETF-QO)

Electron transfer flavoprotein-ubiquinone oxidoreductase (ETF-QO) is a membrane-bound electron transfer protein that links primary flavoprotein dehydrogenases with the main respiratory chain. Human, porcine, and Rhodobacter sphaeroides ETF-QO each contain a single [4Fe-4S](2+,1+) cluster and one equivalent of FAD, which are diamagnetic in the isolated enzyme and become paramagnetic on reduction with the enzymatic electron donor or with dithionite. The anionic flavin semiquinone can be reduced further to diamagnetic hydroquinone. The redox potentials for the three redox couples are so similar that it is not possible to poise the proteins in a state where both the [4Fe-4S](+) cluster and the flavoquinone are fully in the paramagnetic form. Inversion recovery was used to measure the electron spin-lattice relaxation rates for the [4Fe-4S](+) between 8 and 18K and for semiquinone between 25 and 65K. At higher temperatures the spin-lattice relaxation rates for the [4Fe-4S](+) were calculated from the temperature-dependent contributions to the continuous wave linewidths. Although mixtures of the redox states are present, it was possible to analyze the enhancement of the electron spin relaxation of the FAD semiquinone signal due to dipolar interaction with the more rapidly relaxing [4Fe-4S](+) and obtain point-dipole interspin distances of 18.6+/-1A for the three proteins. The point-dipole distances are within experimental uncertainty of the value calculated based on the crystal structure of porcine ETF-QO when spin delocalization is taken into account. The results demonstrate that electron spin relaxation enhancement can be used to measure distances in redox poised proteins even when several redox states are present.     

Analytic properties of the scattering amplitude and resonances parameters in a meson exchange model

The analytic properties of scattering amplitudes provide important information. Besides the cuts, the poles and zeros on the different Riemann sheets determine the global behavior of the amplitude on the physical axis. Pole positions and residues allow for a parameterization of resonances in a well-defined way, free of assumptions for the background and energy dependence of the resonance part. This is a necessary condition to relate resonance contributions in different reactions. In the present study, we determine the pole structure of pion–nucleon scattering in an analytic model based on meson exchange. For this, the sheet structure of the amplitude is determined. To show the precision of the resonance extraction and discuss phenomena such as resonance interference, we discuss the S₁₁ amplitude in greater detail.     

The Effects of an Impurity in an Ising‐XXZ Diamond Chain on Thermal Entanglement,on Quantum Coherence,and on Quantum Teleportation

The effects of an impurity plaquette on the thermal quantum correlations measurement by the concurrence, on quantum coherence quantified by the recently proposed l₁‐norm of coherence and on quantum teleportation in a Ising‐ $XXZ$ diamond chain are discussed. Such an impurity is formed by the $XXZ$ interaction between the interstitial Heisenberg dimers and the nearest‐neighbor Ising coupling between the nodal and interstitial spins. All the interaction parameters are different from those of the rest of the chain. By tailoring them, quantum entanglement and quantum coherence can be controlled and tuned. Therefore, the quantum resources—thermal entanglement and quantum coherence—of the model exhibit a clear performance improvement in comparison to the original model without impurities. It is demonstrated that quantum teleportation can be tuned by its inclusion. Thermal teleportation is modified in a significant way as well, and a strong increase in the average fidelity is observed. The exact solution is furnished by the use of the transfer‐matrix method.